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LE arthrology guide

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Samhaley16

Lower Extremity Joints

Santé & Médecine
1  sur  140
Arthrology Guide to the Joints of the Lower Extremity Clinical Anatomy II, Summer 2015 Table 15 Sarah Burkhardt, Trey Downey, Steven Hennig, Sam Jensen, Danielle Meier, Jamie Parsons, Kristen Sanchez, Caitlyn Tivy Table of Contents
1 Hip Complex……………………………………………………………………………...p. 2 Femoroacetabular Joint…………………………………………………………...p. 7 Sacroiliac Joint……………………………………………………………………p. 21 Pubic Symphysis………………………………………………………………….p. 28 Knee Complex…………………………………………………………………………….p. 32 Tibiofemoral Joint………………………………………………………………...p. 39 Patellofemoral Joint………………………………………………………………p. 53 Proximal Tibiofibular Joint……………………………………………………….p. 58 Ankle and Foot Complex………………………………………………………………….p. 62 Distal Tibiofibular Joint…………………………………………………………..p. 62 Talocrural Joint…………………………………………………………………...p. 68 Subtalar Joint……………………………………………………………………..p. 76 Transverse Tarsal Joint…………………………………………………………...p.85 Talonavicular Joint Calcaneocuboid Joint Cuneonavicular Joint……………………………………………………………...p. 94 Cuboideonavicular Joint…………………………………………………………..p. 101 Intercuneiform and Cuneocuboid Complex………………………………………p. 107 Tarsometatarsal Joints…………………………………………………………….p. 113 Intermetatarsal Joints……………………………………………………………..p. 121 Metatarsophalangeal Joints……………………………………………………….p. 125 Interphalangeal Joints of the Foot………………………………………………...p. 133 References…………………………………………………………………………………p. 140 Hip Complex The hip region, or pelvic girdle (Fig. 1), consists of the femoroacetabular (hip) joints, the sacroiliac joints and the pubic symphysis, which work together to serve as the connection between the
2 Fig. 1: The pelvic girdle, posterior view trunk and the lower extremities. The two halves of the pelvic ring are formed by the innominate bones; each innominate is a fusion of three smaller bones: the ilium, the ischium, and the pubis. These halves join anteriorly at the pubic symphysis and posteriorly at the bilateral sacroiliac joints; the pelvis connects to the lower limbs via the hip joints. The location and structure of these joints in the mature skeleton are influenced by weight-bearing activities: the pelvis functions to transfer forces from the trunk to the lower extremities as well as from the ground into the axial skeleton. The three joints of the pelvis are innervated by branches of the lumbar and sacral plexuses and receive their blood supply from branches of the internal and external iliac arteries. The following sections describe the arthrology of these joints and the muscles acting on each. Table 1: Muscles of the Hip Region Muscles Proximal Attachment Distal Attachment Innervation Action Muscles of the Back Erector Spinae Sacrum, iliac crest, spinous processes L5- T11, supraspinous ligament Angles of ribs to costal angles Dorsal rami of the spinal nerves Extension & lateral flexion of the vertebral column Multifidus (transversos pinalis) Sacrum, posterior SI ligament, posterior iliac spine, transverse processes More superior spinous processes Dorsal rami of the spinal nerves Extension & contralateral rotation of the vertebral column Latissimus Dorsi Spinous processes of inferior 6 thoracic vertebrae, thoracolumbar fascia, iliac crest, and inferior 3-4 ribs Floor of intertubercular sulcus of humerus Thoracodorsal nerve (C6,C7,C8) Extends, adducts, and medially rotates humerus; raises body toward arms during climbing Abdominal Muscles- Anterior Wall
3 External Oblique External surfaces of 5th - 12th ribs Linea alba, pubic tubercle, anterior half of iliac crest Thoracoabdo minal nerves (T7-T11) and subcostal nerve Flexes and rotates trunk Internal Oblique Thoracolumbar fascia, anterior ⅔ of iliac crest, and connective tissue deep to lateral third of inguinal ligament Linea alba with aponeurosis of internal oblique, pubic crest, and pecten pubis via conjoint tendon Thoracoabdo minal nerves (ant. rami of T6-T12) and first lumbar nerves Compresses and supports abdominal viscera Rectus Abdominis Pubic symphysis and pubic crest Xiphoid process and 5th - 7th costal cartilages Thoracoabdo minal nerves (ventral rami of T6 - T12) Flexes trunk and compresses abdominal viscera; stabilizes and controls tilt of pelvis Transversus Abdominus Internal surfaces of 7th - 12th costal cartilages, thoracolumbar fascia, iliac crest, and deep to lateral third of inguinal ligament Linea alba with aponeurosis of internal oblique, pubic crest and pecten pubis via conjoint tendon Thoracoabdo minal nerves (ant. rami of T6-T12) and first lumbar nerves Compresses and supports abdominal viscera Anterior Femoral Muscles Iliopsoas- Iliacus Iliac fossa, iliac crest, sacral ala Femur just distal to lesser trochanter Lumbar plexus ([L1], L2-3-4) Flexes hip and stabilizes hip joint Iliopsoas- Psoas Major Anterior transverse processes, vertebral bodies and discs (T12- L5) Lesser trochanter Ventral rami L1-4 (from lumbar plexus) Flexes hip and stabilizes hip joint
4 Rectus Femoris Anterior inferior iliac spine & groove superior to the acetabulum The base of the patella Femoral nerve (L2-3-4) Flexes hip and extends knee Sartorius Anterior superior iliac spine Medial aspect of the proximal tibia Femoral nerve (L2-3 [4]) Flexes, abducts and laterally rotates hip, and flexes and assists medial rotation of the knee Tensor Fascia Latae Anterior superior iliac spine and external lip of iliac crest Iliotibial Tract Superior gluteal nerve (L4-5-S1) Abducts, flexes and medially rotates hip, and assists in maintaining knee extension Medial Femoral Muscles Adductor Brevis Inferior pubic ramus Distal 2/3 pectineal line & medial lip linea aspera Obturator nerve (L2-3- 4) Adducts and flexes hip Adductor Longus Pubic crest Medial lip linea aspera Obturator nerve (L2-3- 4) Adducts and flexes hip Adductor Magnus Inferior pubic ramus, ischial ramus and tuberosity Gluteal tuberosity, linea aspera, medial supracondylar ridge and adductor tubercle of the femur Adductor region: Obturator nerve (L2-3- 4) Tibial division of the sciatic nerve (L4-5- S1) Adducts, flexes (adductor part) and extends (hamstring part) hip Gracilis Body of the pubis and Medial surface of tibia, distal Obturator nerve (L2-3- Flexes and medially
5 inferior pubic ramus to condyle, proximal to insertion of semitendinosus , lateral to insertion of Sartorius 4) rotates the knee and adducts hip Pectineus Superior pubic ramus Femur between the lesser trochanter and linea aspera (pectineal line) Femoral nerve and obturator nerve (L2-3- 4) Adducts and flexes hip Quadratus (Obturator) Externus Rami of pubis and ischium; external surface obturator membrane Trochanteric fossa Obturator nerve (L3-4) Laterally rotates hip Muscles of the Gluteal Region Superior Gemellus External surface of ischium via obturator internus tendon Greater trochanter Sacral plexus (L5-S1-2) Laterally rotates hip Inferior Gemellus Proximal ischial tuberosity via obturator internus tendon Greater trochanter Sacral plexus (L4-5-S1[2]) Laterally rotates hip Gluteus Maximus Aponeurosis of the erector spinae, sacrum, sacrotuberous ligament and posterior gluteal line (innominate) Greater trochanter, gluteal tuberosity of the femur and iliotibial tract Inferior gluteal nerve (L5-S1-2) Extends and laterally rotates hip Gluteus Medius External iliac surface Oblique ridge on the lateral aspect of the Superior gluteal nerve (L4-5-S1) Abducts and medially rotates hip and
6 greater trochanter; gluteal aponeurosis keeps the pelvis level when opposite leg is raised Gluteus Minimis External iliac surface and margin of the greater sciatic notch Anterolateral aspect of the greater trochanter Superior gluteal nerve (L4-5-S1) Abducts and medially rotates hip and keeps the pelvis level when opposite leg is raised Obturator Internus Anterolateral wall of the pelvis and obturator membrane Medial surface of the greater trochanter Nerve to the obturator internus (from the sacral plexus) (L5- S1-2) Laterally rotates hip Piriformis Anterolateral sacrum and post inf iliac spine Upper border of the greater trochanter Branch of the lumbosacral plexus ([L5]S1-2) Abducts and laterally rotates hip Quadratus Femoris Ischial tuberosity Quadrate tubercle of the femur Nerve to the quadratus femoris (from sacral plexus) (L4-5-S1[2]) Laterally rotates hip Posterior Femoral Muscles Biceps Femoris Long head: ischial tuberosity and sacrotuberous ligament Short head: lateral lip of linea aspera and lateral supracondylar line Lateral side of the fibular head Long head: Tibial branch of sciatic nerve (L5-S1- 2-3) Short head: Peroneal branch of sciatic nerve (L5-S1-2) Both heads: Flex knee Long Head: Extends hip Semimembr anosus Ischial tuberosity Posterior aspect of the Tibial division of the sciatic Extends hip and flexes and
7 Fig 2: Intra-articular view of the femoroacetabular joint medial tibial condyle nerve (L4-5- S1-2) medially rotates knee Semitendino sus Ischial tuberosity Proximal, medial tibia Tibial division of the sciatic nerve (L4-5- S1-2) Extends hip, and flexes and medially rotates knee Femoroacetabular Joint The femoroacetabular, or “hip”, joints are bilateral diarthrodial synovial ball-and-socket joints between the head of the femur and the acetabulum of the pelvis (Fig. 2). The hip is the second most mobile joint in the body, second only to the glenohumeral joint. The hip and the shoulder joints are often compared to due to their common classification as ball-and-socket joints, but the hip is less mobile and more stable than the shoulder. This small mobility-to-stability ratio supports the primary function of the hip joint in providing support to the weight of the trunk, head and upper limbs while in weight-bearing positions. Branches from the obturator artery, lateral circumflex femoral arteries, and superior and inferior gluteal arteries supply the hip joint with blood, while branches from the lumbar and sacral nerve plexuses provide its innervation. The following list describes the tissue layers of the femoroacetabular joints from superficial to deep, as well as the neurovasculature and other structures associated with the joints. Tissue Layers of the Femoroacetabular Region (Superficial to Deep) ● Cutaneous ○ Skin (cutis) ■ Epidermis ■ Dermis ● Subcutaneous ○ Superficial Fascia ○ Deep Fascia ○ Iliotibial band ● Muscles and tendons ○ Extension ■ Gluteus maximus ■ Biceps femoris ■ Semitendinosus ■ Semimembranosus ■ Adductor magnus
8 ○ Flexion ■ Sartorius ■ Tensor fascia latae ■ Rectus femoris ■ Pectineus ■ Adductor Longus ■ Iliopsoas ○ Adduction ■ Pectineus ■ Gracilis ■ Adductor brevis ■ Adductor longus ■ Adductor magnus ○ Abduction ■ Tensor fascia latae ■ Gluteus medius ■ Gluteus minimus ○ External Rotation ■ Gluteus maximus ■ Piriformis ■ Gemellus superior ■ Gemellus inferior ■ Obturator internus ■ Quadratus femoris ● Neurovascular Supply ○ Nerves ■ Lumbar Plexus □ Femoral nerve □ Obturator nerve ■ Sacral Plexus □ Nerve to the piriformis □ Nerve to the obturator internus and gemellus superior □ Nerve to the quadratus femoris and gemellus inferior □ Superior and inferior gluteal nerves □ Sciatic nerve ○ Arteries ■ Branches of: □ Obturator □ Femoral ● Medial and lateral circumflex □ Superior and inferior gluteal □ First perforating artery of profunda femoris artery ○ Veins ■ Great saphenous vein ■ Femoral vein ● Ligaments
9 Fig. 3: Joint Capsule of the Disarticulated Hip ○ Iliofemoral ligament ○ Pubofemoral ligament ○ Ischiofemoral ligament ○ Transverse acetabular ligament ○ Ligament of head of femur ● Joint Capsule The joint capsule of the hip is a large, strong structure attached to the acetabular rim, the intertrochanteric line, and the posterior surface of the posterior femoral neck. The capsule encloses the femoral head and most of the femoral neck, and it is relatively loose to allow for joint movements. The capsule’s internal fibers are orientated in a circular fashion, whereas the external fibers run longitudinally. The head of the femur is covered with articular hyaline cartilage, except at the fovea capitis, where the ligament of the head of the femur attaches to the femoral head. The articular cartilage of the femoral head is thickest where it bears the most weight: on its anterior and lateral surfaces and superior to its center. The acetabulum of the pelvis includes components of the iliac, ischial, and pubic bones, and it is covered by articular hyaline cartilage on its lunate surface; the half moon-shaped surface is bounded by the acetabular rim and the edge of the acetabular fossa, which is filled by a fat pad. The acetabular labrum consists of fibrocartilage lining the bowl of the acetabulum and serves to increase the stability of the joint. ● Bones ○ Femur ■ Femoral head ■ Femoral neck ■ Greater and lesser trochanters ○ Innominate ■ Ischium, ilium pubis Joint Motions The physiologic motions of the hip joint include flexion, extension, adduction, abduction, rotation, and circumduction; many of its movements are multiaxial. When the hip reaches full extension, simultaneous medial rotation occurs and acts as a “locking” mechanism to bring the femoral head into full congruence with the acetabulum. This type of movement is termed conjunct rotation. The accessory movements that occur between the joint surfaces are described in the section below on arthrokinematics. Table 2: Physiologic Motions of the Hip Joint and the Associated Muscles Joint motion Associated Muscles Flexion Iliopsoas, Rectus femoris, Sartorius,
10 Pectineus, Adductor longus and brevis, Tensor fascia latae, Gluteus minimus Extension Gluteus maximus, Gluteus medius (posterior fibers), Biceps femoris, Semitendinosus, Semimembranosus, Piriformis, Adductor magnus (posterior fibers) Abduction Gluteus medius, Tensor fascia latae, Gluteus minimus, Iliopsoas, Piriformis, Superior gemellus, Inferior gemellus, Obturator internus Adduction Adductor longus and brevis, Adductor magnus, Pectineus, Gracilis Medial rotation Tensor fascia latae, Gluteus medius (anterior fibers), Adductor longus and brevis, Gluteus minimus Lateral rotation Piriformis, Superior gemellus, Inferior Gemellus, Obturator internus and externus, Gluteus maximus, Sartorius, Biceps femoris (long head), Iliopsoas, Gluteus medius (posterior fibers) Planes of motion As stated previously, the hip joint functions to stabilize the head, arms and trunk during static and dynamic activities. The joint allows for three degrees of freedom, or movement in three planes, as described in Table 3. Table 3: Planes of Physiologic Motion at the Hip Plane Axis Motion Sagittal Medial-lateral Flexion and extension Frontal Anterior-posterior Abduction and adduction Transverse Longitudinal (vertical) Medial and lateral rotation The convex head of the femur articulates superiorly with the concave socket of the acetabulum and inferiorly with the fovea. The center-edge angle, a measurement commonly used in the field of orthopedic surgery, defines the fixed orientation of the acetabulum relative to the pelvis in the frontal plane. This measurement gives clinicians an indication of the percent of the femoral head that is covered by the acetabulum; it is commonly used in the diagnosis of hip dysplasia. The articular surface of the acetabulum, the lunate surface, is oriented in an anterior- inferior direction. The angle at which the femoral head articulates with the acetabulum is referred to as the angle of inclination.
11 Fig. 4: Angle of Inclination of the Hip Joint Angle of Inclination The angle of inclination of the hip provides information regarding the alignment of the femoral head within the acetabulum. This angle is measured in the frontal plane between the femoral neck and the femoral shaft. The magnitude of the angle decreases naturally from about 145 degrees at the time of birth to about 125 degrees in the skeletally mature adult. This decrease is due in part to the forces acting on the femur during weight bearing and partially to the increase in muscular pull on the femur as the child’s muscles develop and his or her activity level increases. An angle of inclination greater than 125 degrees is termed coxa valga (Fig. 4); it is correlated with a lengthening of the limb, an increased load on the femoral head and less-than- optimal line of pull for the hip abductors. If the angle of inclination is less than 125 degrees, the femoral neck experiences increased loading forces and the limb is shortened, but the line of pull for the abductor musculature is actually improved. This presentation is termed coxa vara (Fig. 4). Femoral Torsion Femoral torsion describes the angle formed between the longitudinal axis of the head, neck, and greater trochanter of the femur and the transverse axis of the femoral condyles when the femur is viewed along the axis of its shaft (Fig 5.). The typical angle of torsion in adults is slightly anteverted (8 - 15 degrees). Infants typically demonstrate 40 degrees of anteversion; this anteversion decreases as movement patterns and muscular lines of pull change with development. An adult with more than 15 degrees of anteversion is considered to have excessive anteversion; this configuration will result in
12 Fig. 5: Angle of Torsion of the Femur Fig. 6: Biomechanical Consequences of Atypical Angles of Torsion compensatory internal rotation of the hip in order to provide better congruency at the hip joint. This commonly results in an in-toeing gait pattern in these individuals. The following illustration demonstrates the relationship between femoral torsion and the functional position of the lower extremity. As shown in Figure 6, a retroverted hip occurs when the angle of torsion is less than 15 degrees (often close to zero degrees), and results in “toeing out”. When the angles of inclination and femoral torsion are within the appropriate ranges, the articulation between the femoral head and the acetabulum exhibits optimal biomechanics and may place the joint at a decreased risk for degeneration. Biomechanics and Kinematics The motion that occurs at this joint can be subdivided into femoral-on-pelvic osteokinematics and pelvic-on-femoral osteokinematics, depending on which bony structure is fixed and which is mobile. The biomechanics are described relative to the anatomical position, and each motion has a specific axis of rotation. When motion occurs in the closed kinetic chain, as during the stance phase of gait, the pelvis is moving on a fixed femur. Conversely, motion in the open kinetic chain features the femur moving on a stable pelvis, as during the swing phase of gait. The convex-concave rules of biomechanics can be applied to this ball-and-socket joint in order to better understand the motions that occur in the open and closed kinetic chains. These rules describe the arthrokinematic (joint) motions that occur in conjunction with the primary physiologic (osteokinematic) motions described in Table 3. The three chief arthrokinematic motions that can occur within a given joint are rolling, sliding, and spinning. Rolling occurs when multiple points on one articulating surface come into contact with multiple points on the other. Sliding features a solitary point on one articular surface contacting multiple points on the other. These arthrokinematic motions are illustrated in Figures 7 and 8. Spinning (not pictured here) entails a single point of one articular surface rotating on single point of the other. Arthrokinematics: Convex-on-Concave Rule When a convex surface is mobile relative to a fixed concave surface, the two surfaces roll and slide in opposite directions.
13 Fig. 7: Convex on Concave Arthrokinematics Fig. 8: Concave on Convex Arthrokinematics For example, when the convex head of the femur articulates with the fixed concave surface of the acetabulum during open chain hip flexion, the femoral head rolls superiorly and slides inferiorly. This motion occurs during activities such as walking, kicking or stepping over an object. Arthrokinematics: Concave-on-Convex Rule A concave surface moving on a fixed convex surface results in the rolling and sliding of two surfaces in the same direction. As the mobile, concave surface of the acetabulum moves while the convex surface of the femoral head is fixed, the two entities roll and glide in the same direction. Bending over while standing and leaning backwards while sitting in a chair are examples of this type of motion. Femoral–on-Pelvic Kinematics Hip flexion occurs in the sagittal plane with an average range of motion of 120 degrees. Hip flexion is limited at end range primarily by approximation of the soft tissues of the thigh and abdomen; less motion available if the knee is extended due to the stretch placed on the two-joint hamstring muscle group. During hip flexion, the round head of the femur moves in an inferoposterior direction within the acetabulum, thereby stretching the joint’s inferior capsule and posterior musculature. During hip extension, the femoral head moves anteriorly, increasing
14 Fig. 9: Sagittal Plane Motion at the Femoroacetabular Joint Fig. 10: Frontal Plane Motion at the Femoroacetabular Joint the tension on the anterior ligaments and hip flexor muscles. Typical hip extension range of motion is limited to 20 degrees, with even less motion available when the knee is flexed, due to the passive tension placed on the two-joint rectus femoris muscle. During abduction and adduction in the frontal plane, the femoral head and the distal portion of the femur move in opposite directions. As the thigh abducts, the femoral head rolls and slides inferomedially within the acetabulum; this arthrokinematic motion permits about 40 degrees of osteokinematic abduction. Abduction range of motion is primarily restricted by the pubofemoral ligament and the maximal stretch placed on the adductor musculature. Conversely, as the hip adducts, the head of the femur rolls and slides superolaterally, allowing the distal end of the femur to swing medially. Hip adduction range of motion is limited to 25 degrees and is limited as a result of stretched hip abductor musculature, the iliotibial band and the ischiofemoral ligament.
15 Fig. 11: Horizontal Plane Motion at the Femoroacetabular Joint Rotation of the femur on the acetabulum occurs in the horizontal (transverse) plane. It is expected that the hip’s range of motion into external rotation will exceed that of internal rotation. When the hip is fully internally rotated, the ischiofemoral ligament and the external rotator muscles are maximally stretched, thereby limiting internal rotation to about 35 degrees of motion. As the femur rotates externally, the stretch placed on the internal rotation musculature and the iliofemoral ligament allows for about 45 degrees of external rotation. Pelvi c-on-femoral osteokinematics The attachment of the axial skeleton to the pelvis creates a relationship between the pelvis, as it moves over the femoral heads, and the lumbar spine known as lumbopelvic rhythm. Ipsidirectional lumbopelvic rhythm occurs as the lumbar spine and pelvis move in the same direction, as when a person is bending forward to pick up an object from the floor. The associated displacement of the trunk helps to maximize functional movement. During contradirectional lumbopelvic rhythm, the pelvis will move one direction as the lumbar spine moves in the opposite direction. This relationship ensures that the head and trunk remain relatively stable while the pelvis rotates during ambulation. When the concave articular surfaces of the acetabulum move over the convex femoral heads, the resulting sagittal plane motions are described as anterior and posterior pelvic tilts. In the seated position (with 90 degrees of hip flexion), the iliac crests shift anteriorly to allow approximately 30 degrees of pelvic-on-femoral hip flexion; this shift establishes an anterior pelvic tilt. This anterior tilt forces the lumbar spine into a greater degree of lordosis. Along with restriction by the ligamentous scaffolding of the pelvic girdle, this increased lumbar lordosis ultimately limits further anterior displacement of the pelvis. In the standing position, anterior tilt is restricted by the hamstring muscles; the degree of restriction varies with an individual’s hamstring flexibility. Although osteokinematic hip extension is limited to 20 degrees, additional functional hip extension can be achieved by combining a posterior pelvic tilt with flexion of the lumbar spine. The posterior tilt of the pelvis increases the length in the iliofemoral ligament and rectus femoris muscle which provides “slack”, thereby reducing the resistance into extension. Range of motion into extension is limited by the iliofemoral ligament and passive tension from the rectus femoris muscles.
16 Fig. 13: Posterior Pelvic TiltFig. 12: Anterior Pelvic Tilt In the frontal plane, pelvic-on-femoral osteokinematics occur via a lateral tilting of the pelvis on the fixed femur. Single leg stance activities provide a clear demonstration of these motions: when the iliac crest of the non-stance limb moves superiorly, the lateral tilt is described as a “hip hike”, whereas an inferior translation of the iliac crest is termed “hip drop”. During the single leg stance phase of the typical gait pattern, pelvic-on-femoral abduction occurs as the iliac crest of the non-stance limb moves superiorly (a hip hiking motion), resulting in relative abduction of the stance leg. The lumbar spine must laterally flex towards the hiked hip to accommodate this motion and maintain the body’s center of mass within the its limits of stability (Fig. 14). An individual’s range of motion into lumbar lateral flexion is a limiting factor for his or her range into relative abduction. Other factors, including adductor muscle contracture/tightness and the passive restraint provided by the pubofemoral ligament, restrict pelvic-on-femoral abduction range of motion to 30 degrees or less. As the iliac crest of the non-stance leg moves inferiorly (a hip dropping motion), the stance leg shifts into relative adduction; the lumbar spine now laterally flexes away from the dropped hip (Fig. 14). The individual’s range of motion into lumbar lateral flexion again constrains the available range into relative adduction. Limited extensibility of the iliotibial band and hip abductor musculature can also restrict this motion. Pathologic motion can also result in what is known as compensated and uncompensated Trendelenburg Gait, which can be observed during the stance phase of the gait cycle. Compensated Trendelenburg occurs when the subject leans ipsilaterally to the side of the stance leg. If the person’s contralateral pelvis drops (when viewed in the frontal plane), this is described as an uncompensated Trendelenburg gait. During the stance phase of the gait cycle, the gluteus medius muscle, along with the other hip abductors, is responsible for keeping the pelvis in a neutral position as the body weight is loaded onto the stance leg. When this muscle group is weak or its innervation is disrupted, its function can be compromised to the point where these obvious changes in the gait cycle occur.
17 Fig. 14: Frontal Plane Osteokinematics of the Pelvis on the Stable Femur Fig. 15: Horizontal Plane Osteokinematics of the Pelvis on the Stable Femur Rotational motion of the pelvis on the femur in the horizontal plane can also be described in reference to single leg stance activities. As the iliac crest of the non-stance limb moves anteriorly in the horizontal plane, the stance limb hip moves into relative internal rotation. Conversely, posterior translation of the iliac crest of the non-stance limb results in relative external rotation of the stance limb hip (Fig. 15). The lumbar spine moves in synergy with the rotating pelvis by rotating itself in the contralateral direction. Table 4: Ligaments of the Femoroacetabular Joint Ligament Proximal attachment Distal attachment Function Ligamentum teres Acetabular notch Fovea of femur Conduit for neurovasculature of the femoral head Iliofemoral (Y ligament) Anterior inferior iliac spine Intertrochanteric line of the femur Controls external rotation in flexion, internal and external
18 Fig. 16: Comparison of the Healthy and Osteoarthritic Hip Joint rotation in extension, limits anterior translation of femoral head Pubofemoral Anterior pubic ramus Intertrochanteric fossa Controls external rotation in extension Ischiofemoral Posterior surface of the acetabular rim and labrum Capsular fibers, medial surface of greater trochanter Controls internal rotation in hip flexion and extension Common Pathologies of the Femoroacetabular Joint Hip Osteoarthritis (OA) is becoming an increasingly common pathology in the United States as the average age of the population continues to increase. OA of the hip involves degeneration of the femoral and acetabular articular cartilages, ultimately leading to a narrowing of the joint space over time. Approximately 50% of the cases of hip OA are of unknown etiology and cannot be linked to any one cause, although a history of injury to the hip joint, obesity, and the natural aging process are common predisposing factors. Typical symptoms, especially in individuals over the age of 50, include stiffness that is worse in the morning but is relieved with movement; anterior groin pain; decreased range of motion into extension, internal rotation and end range flexion; antalgic gait; and pain with activities of daily living. Altman’s Criteria for Hip OA are used as a diagnostic tool to help practitioners identify the nature of a patient’s condition without imaging (Table 5). Altman’s Criteria for hip OA has a specificity of 75% and a positive likelihood ratio of 3.4. Thus, if a patient meets all three criteria in either cluster, hip OA is the likely diagnosis. Surgical and non-surgical courses of treatment are available for treatment of hip OA. Table 5: Altman’s Criteria for Hip OA
19 Fig. 18: Radiograph depicting a Left Displaced Femoral Neck Fracture Fig. 17: Possible Presentations of Femoral Acetabular Impingement Cluster 1 Cluster 2 Hip pain AND Painful hip IR > 15 degrees AND Hip IR <15 degrees AND Age> 50 years old AND Flexion < 115 degrees Stiffness in the morning < 60 min duration Femoral acetabular impingement (FAI) can occur as the result of repetitive microtrauma to the labrum, articular cartilage and bone, secondary to an abnormal acetabular structure or femoral articulation. Three different types of FAI exist: pincer type, cam type, and a mixed type featuring elements of both of the former (Fig. 17). Pincer type FAI typically occurs in middle-aged females and is the result of excessive coverage of the femoral head by the acetabulum. As the femoral head makes repeated contact with the overgrown edges of the acetabulum during hip movement, the posteroinferior articular cartilage of the femoral head is progressively damaged. Cam type FAI is more common in younger males and is the consequence of an abnormal concavity along one side of the femoral head. During femoroacetabular motion, the extra bone growth on the femoral head is repetitively compressed against the lip of the acetabulum, thus producing a shearing force on the labrum over time. Symptoms of FAI include sharp groin pain during hip flexion and internal rotation; posterolateral pain with external rotation; pain when climbing stairs and/or when sitting down; and difficulty with squatting or cutting motions. Femoral fractures are a growing problem in the geriatric population: they commonly occur secondary to a fall, although in patients with extremely osteoporotic bones, the femur may actually fracture before the falling body even contacts the ground. Upon evaluation, it can be
20 Fig. 19: The Sacroiliac Joints within the Pelvic Girdle difficult to discern if the fracture was a direct result of a fall, or if the hip fractured first and caused the person to fall. This ambiguity is further complicated by the patient’s typically poor recall of events following the sudden shock of a fall. A proximal femoral fracture can be sustained along the femoral neck or within the intertrochanteric or subtrochanteric areas. The mechanism of injury is typically compression trauma that is sustained as a result of a direct lateral force to the hip, which can lead to subsequent soft tissue damage and possible hemorrhaging. A femoral neck fracture presents a more complex medical problem, as this type of injury usually compromises the vasculature encircling the neck. When the blood supply to the femoral head is so greatly compromised that it leads to death of the articular cartilage and subchondral bone, the result condition is termed avascular necrosis (AVN); the mortality rate associated with AVN is high, particularly in the elderly population. Sacroiliac Joints The sacroiliac (SI) joints mark the transition point between the axial and appendicular skeletons. These bilateral joints are formed by the joining of the auricular surface of the lateral sacrum and the auricular surfaces of the ilia, at vertebral levels S1-S3. They are planar synovial joints and are very stable due to their strong supporting ligaments. Each SI joint is surrounded by a joint capsule and lined with a synovial membrane. The articular surfaces of the ilia are covered in hyaline cartilage, and the articular surfaces of the sacrum are covered by fibrocartilage; the interaction between these different tissues throughout the aging process can lead to fibrous adhesions across the joint cavity. A number of other changes occur within the aging SI joint. For example, the articular surfaces of the joints are smooth in the newborn, but become more irregular with age due to the loading forces imposed by a variety of weight bearing activities. The SI joint is initially diarthrodial and moves easily, but between puberty and young adulthood, it changes into a modified amphiarthrodial joint, permitting only slight motion. Osteophytes in and around the joint are common, even in the young adult. By the 8th decade, the hyaline cartilage has deteriorated; in some cases, the joint ossifies completely. Degenerative changes may develop secondary to certain pathologies, but they are more often the joint’s natural response to years of weight bearing and force transference. The movement available at the SI joint is limited due to its strong stabilizing ligaments and intrinsic structure of the joint. Females generally have more mobility at this joint than males, and the joint’s range of motion increases during pregnancy and childbirth. In both sexes, however, the movement available at these joints decreases with age.
21 As previously discussed, the role the SI joints play in transferring forces between the trunk and the lower extremities places them under unique structural demands. The SI joints form part of the pelvic ring, which also consists of the sacrum, the innominate bones, and the pubic symphysis. The integrity of the pelvic ring depends on the stability of the sacrum, which lies between the two innominate bones and is connected to them via the SI joints; the stability of the SI joints therefore plays a critical role in maintaining the overall functionality of the pelvic girdle. In addition to serving as a means for load transfer, the SI joint acts a “shock absorber” to attenuate some of the forces the pelvis experiences during loading. Tissue Layers of the Sacroiliac Region (Superficial to Deep) ● Cutaneous ○ Skin (cutis) ■ Epidermis ■ Dermis ● Subcutaneous ○ Superficial fascia ■ Contains fat, cutaneous nerves, superficial veins, lymph vessels, lymph nodes ○ Deep fascia ● Muscular Fascia ○ Thoracolumbar fascia ● Muscles ○ Biceps femoris – long head ○ Erector spinae ○ External and internal obliques ○ Gluteus maximus ○ Iliacus ○ Latissimus dorsi ○ Lumbar multifidus ○ Piriformis ○ Rectus abdominis ○ Transversus abdominus ● Neurovascular Supply ○ Nerves ■ Dorsal rami of sacral nerves S1 – S4 ■ Anterior rami of sacral nerves S1-S2 ■ Superior gluteal nerve ○ Arteries ■ Posterior division of internal iliac arteries □ Iliolumbar arteries □ Lateral sacral arteries □ Superior gluteal arteries ○ Veins ■ Common iliac vein ● Ligaments
22 ○ Anterior Sacroiliac Ligament ○ Interosseous SI Ligament ○ Short and Long Dorsal SI Ligament ○ Iliolumbar Ligament ○ Sacrotuberous Ligament ○ Sacrospinous Ligament ● Joint Capsule ○ Attaches along margins of auricular surfaces of sacrum and ilium and is thickened anteriorly as the anterior sacroiliac ligament. Joint Motions The SI joints allow for a small amount of sacral rotation with respect to the innominate bones. Among experts, controversy abounds concerning the actual amount of motion available at these joints, and the extent to which this movement impacts symptomatic pathology. Synovial joints are generally perceived to be highly mobile, but despite their synovial classification, movement of the SI joint is extremely restricted by its stabilizing ligaments. Along with the pubic symphysis, these joints allow for small rotational and gapping movements, which reduce the stress transferred to the pelvis from the trunk and lower limbs. The principal motions of the SI joints are nutation and counternutation, as discussed in the following sections. Biomechanics and Kinematics The SI joints are regarded as a biomechanical “buffer” between the vertebral column, the lower extremities, and the ground reaction force. The primary functions of the SI joints are as follows: stabilization of the pelvis; transference of gravitational forces acting on the vertebral column to the lower extremities; and distribution and attenuation of ground reaction forces exerted upon the lower extremities during weight bearing. The SI joints are semicircular in shape, and the joint plane is oriented vertically (Fig. 20) near-sagittal plane. The motions of the SI joints are unique in that they are small, difficult to define, and not directly controlled by active contraction of the surrounding musculature. It has been estimated that the total amount of SI joint motion occurring in the mature adult skeleton ranges from 1-4 degrees of rotation and 1-2 mm of translation in the horizontal plane. These ranges can increase significantly during pregnancy as result of the hormonally induced increase in joint laxity required for vaginal delivery of the infant. Due to the complexity of the translational and rotational motions that occur at the SI joint, unique terminology has been adopted to describe its biomechanics. The terms nutation and counternutation describe the near-sagittal plane motions of the SI joint relative to the fixed ilium (Fig. 21). Nutation can be likened to anterior rotation: it refers to a coupling of the inferior and anterior shift of the sacral promontory with the posterior movement of the apex of the sacrum and the coccyx. Conversely, counternutation is comparable to posterior rotation: it describes a relative posterior tilt of the sacral promontory paired with a simultaneous anterior translation of the sacral apex and coccyx. It is important to note that these osteokinematic motions of the SI
23 Fig. 20: Transverse Section through the Sacroiliac Joints Fig. 22: Locking Mechanismof the Fully Nutated SI Joint joints can occur when the sacrum moves on the iliac bones, when the ilia rotate on the sacrum, or when both movements are occurring simultaneously. D urin g nuta tion, the ischi al bone s move apart and the iliac bones are approximated. The opposite occurs during counternutation, as shown in Figure 21. Both nutation and counternutation are limited by various ligaments of the SI joint, which are described in detail in Table 6. When the sacrum is fully nutated, the SI joint is in its close-packed position: that is, there is maximal contact between the joint surfaces and maximal tension across its ligaments. The forces generated by gravity, ligamentous tension, and muscular contraction increase the compressive and shearing forces between the articulating surfaces of the joint. When the sacrum is in full nutation, these compressive forces create optimal stability for the SI joints. During weight bearing, the force of gravity acting through the vertebral column creates a torque that rotates the sacrum anteriorly relative to the ilium. Simultaneously, the compressive force of the femurs against the acetabula acts to rotate the ilia posteriorly relative to the sacrum. This phenomenon is referred to as the nutation torque, and it ultimately results in a “locking” of the SI joint (Figure 22). The nutation torque mechanism demonstrates how motion of the SI joint is dictated primarily by the force of gravity, rather than by the actions of muscles or ligaments. The muscles involved in nutation and counternutation (Table 6) act on either the sacrum or the innominate bones. For example, the erector spinae muscles nutate the sacrum, while the Fig. 21: Physiologic Motions of the Sacroiliac Joints
24 Fig. 23: Ligaments of the Sacroiliac Joint pelvic floor muscles balance their action with reciprocal counternutation. The muscles that act to nutate and counter-nutate the pelvis are detailed in Table 6. Table 6: Physiologic Motions of the SI Joint and the Associated Muscles Joint Motion Associated Muscles Nutation Multifidus, erector spinae, rectus abdominis, biceps femoris, adductor magnus Counternutation Rectus femoris, Sartorius, pectineus, adductor longus, adductor brevis, latissimus dorsi Compression Internal oblique, transversus abdominis Ligaments During vigorous, high impact activities such as running or jumping, greater demands are placed on the SI joint; in these situations, the ligaments and muscles that cross the SI joint play significant roles in its stabilization. The ligaments become stretched as the nutation torque produced by gravity increases. As the tension in these ligaments increases (Fig. 23 and Table 7), the compression forces acting on the SI joint also increase. This direct relationship between ligamentous tension and joint compression force ensures optimal stability of the joint during dynamic tasks. Table 7: Ligaments of the SI Joint Ligament Proximal Attachment(s) Distal Attachment(s) Functions Anterior sacroiliac* Anterior surface of the lateral part of the sacrum Margin of the auricular surface of the Ilium Reinforce anterior and inferior aspects of joint capsule
25 Iliolumbar* Lower part of the transverse processes of the 4th and 5th lumbar vertebrae Anterior part of the upper surface of the sacrum, crest of the ilium Reinforce anterior and inferior aspects of joint capsule Interosseous* Auricular surface of the sacrum Iliac tuberosity Transfer weight of upper body from axial skeleton to the ilia; Resists anterior and inferior movement of the sacrum Short and long posterior sacroiliac* Short: posterior- lateral side of sacrum Long: from regions of 3rd and 4th sacral segments Short: Ilium near iliac tuberosity Long: posterior- superior iliac spine Reinforce the posterior aspect of the joint; Resists counternutation of the sacrum on the ilium during weight bearing Sacrotuberou s Posterior-superior iliac spine, lateral sacrum, and coccyx Ischial tuberosity Indirect (secondary) stabilization of the joint, prevents upward tilting of lower end of sacrum; Resists nutation of the sacrum on the ilium during weight bearing Sacrospinous Lateral margin of caudal end of the sacrum and coccyx Ischial spine Indirect (secondary) stabilization of the joint, prevents upward tilting of lower end of sacrum; Resists nutation of the sacrum on the ilium during weight bearing *indicates primary stabilizing ligaments The thoracolumbar fascia also plays a key role in the stabilization of the SI joint. The posterior layer of the thoracolumbar fascia lies superficial to the erector spinae and the latissimus dorsi, and it attaches to the
26 Fig. 24: Transverse Section Depicting the Layers of the Thoracolumbar Fascia Fig. 25: Fortin’s Area Fig. 26: Radiograph of a Right SI Joint Dislocation spinous processes of the five lumbar vertebrae, the sacrum, and the ilia (Fig. 24). Due to its direct attachment to both the sacrum and the ilia, this layer of the thoracolumbar fascia provides critical mechanical stability to the SI joint. Common Joint Pathology SI joint pain has been reported in 15-30% of patients who present with low back pain. Although the pattern of pain referral from the SI joint tends to be variable, a common location of referred pain is the region immediately inferior to the posterior inferior iliac spine; a presentation of loc aliz ed pain 1 cm posterior to the PSIS is referred to as Fortin’s sign (Fig. 25). Although it is poorly understood, the primary mechanism of injury to the SI joint is thought to be the result of axial loading in combination with rotation. SI pain can also be the consequence of a vast array of pathological changes, including capsular and ligamentous tension, hypo- or hypermobility, abnormal joint mechanics, soft tissue injury, and inflammation. Common intra- articular pain generators include osteoarthritis and infection, whereas fractures, ligamentous injury, and myofascial pain are categorized as extra-articular sources of pain. Risk factors for the development of SI joint pain include leg length discrepancy, gait or postural abnormalities, prolonged vigorous exercise, scoliosis, spinal fusion to the sacrum, pregnancy, and repetitive and unidirectional high velocity motions, (i.e. kicking, swinging, throwing). Direct injury and dislocations of the SI joint can occur secondary to sudden traumatic or shearing forces, as occur when a person unexpectedly steps down from a high curb or into a hole, or falls directly onto the SI joint (Fig. 26). Pubic Symphysis The pubic symphysis is a cartilaginous joint located at the inferior aspect of the abdomen, just superior to the external genitalia; it forms the interface between the two pubic bones. The medial symphyseal surfaces of the pubic bones are separated by a fibrocartilaginous disc. These joint surfaces are covered with hyaline articular cartilage that blends with the disc. The joint is minimally mobile and is thus classified as a synarthrosis. The main function of the pubic symphysis is the absorption and attenuation of forces throughout the anterior pelvic ring,
27 especially during weight bearing activities and the acute stresses induced by pregnancy and childbirth. The following list describes the tissue layers of the pubic symphysis, superficial to deep, as well as the neurovasculature and other structures associated with the joint. Tissue Layers of the Pubic Symphyseal Region (Superficial to Deep) ● Cutaneous ○ Skin (cutis) ■ Epidermis ■ Dermis ● Subcutaneous Tissue ● Superficial Fascia ○ Camper’s Fascia ■ Mons pubis ○ Scarpa’s Fascia ● Muscles ○ Rectus abdominus ○ Abdominal external oblique ○ Abdominal internal oblique ○ Transversus abdominis ○ Gracilis ○ Pectineus ○ Adductor longus ○ Adductor brevis ○ Adductor magnus ● Neurovascular Supply ○ Nerves ■ Branches of: □ Iliohypogastric □ Ilioinguinal □ Pudendal □ Genitofemoral ○ Arteries ■ Branches of: □ Obturator □ Inferior epigastric □ Pudendal ○ Veins ■ Internal iliac vein ● Ligaments ○ Anterior pubic ligament ○ Posterior pubic ligament ○ Inferior pubic (arcuate) ligament ○ Superior pubic ligament ● Joint Capsule
28 Fig. 27: Ligaments of the Pubic Symphysis, Schematic Biomechanics and Kinematics As a cartilaginous synarthrosis, the adult pubic symphysis permits a very small amount of rotation and translation under normal physiologic conditions. The joint’s wedge-shaped fibrocartilaginous disc is wider superiorly and inferiorly and more narrow in the middle with its apex is directed posteriorly. The disc functions to resist tensile, shearing and compressive forces within the joint. The width of the joint space ranges from 3 – 10 mm and varies with age and gender. The articular surfaces are convex, ovular in shape, and are oriented obliquely within the sagittal plane. During functional activities like standing, sitting and single leg stance, the pubic symphysis experiences compressive, traction, and shearing forces. Due to the small magnitude of movement permitted at this joint, research regarding the biomechanics of this joint is scarce. A 2010 study by Becker, et al. reported that less than one degree of rotation occurs about the sagittal axis in the coronal plane and about the horizontal axis in the sagittal plane. Table 8: Ligaments of the Pubic Symphysis Ligament Attachment(s) Functions Superior pubic ligament Superior aspects of pubic bodies, interpubic disc, pubic tubercles Joint stability and reinforcement Inferior pubic (subpubic or arcuate) ligament Inferior pubic rami, interpubic disc, posterior pubic ligaments Forms the apex of the pubic arch Anterior public ligament Periosteum laterally, interpubic disc Joint stability and reinforcement Posterior pubic ligament Periosteum of pubic bodies posteriorly Joint stability and reinforcement
29 Fig. 28: Ligaments of the Pubic Symphysis, In Situ Fig. 29: Radiograph of a Pelvis with Dysfunction of the Pubic Symphysis Fig. 30: Non-grid Pelvic Support Belt Used to Support the Pelvis of Pregnant Women with Symphysis Pubis Dysfunction Common joint pathology Symphysis pubis dysfunction, which commonly occurs during pregnancy, is defined as mild to severe pain in the pubic region, the groin, and the medial aspect of the thigh. This pain often co-occurs with sacroiliac, low back and suprapubic pain, and it can profoundly affect the woman’s quality of life. Patients with this dysfunction may demonstrate a “waddling” gait adopted in an attempt to attenuate the pain and possible clicking or grinding sensations associated with weight bearing activities. The increased release of reproductive hormones during pregnancy induces greater laxity in the supportive ligaments of the pelvis; as a result, the entire pelvic girdle becomes increasingly unstable as pregnancy progresses. A study conducted by Depledge, et al found that exercise and the use of a non-grid pelvic support belt (Fig. 30) reduced the subjects’ pain and increased their functional mobility. Osteitis pubis is a common pathology among athletes, particularly soccer and hockey players. Osteitis pubis is a non-infectious inflammatory condition of the symphysis pubis that can also occur following trauma or secondary to rheumatic disorders or pregnancy. Pain typically refers to the groin, the lower abdomen, and/or the region directly superficial to the pubic symphysis. In the athletic population, this condition can occur as the result of mechanical traction microtrauma caused by an imbalance between the abdominal muscles and the hip adductors. The patient will often complain of pain during resisted hip adduction and active contraction of the abdominal
30 Fig. 31: Bone Scan (left) and CT Scan (right) of a Pelvis with Osteitis Pubis muscles. Bone scans will reveal elevated isotope uptake at the pubic symphysis (Fig. 31, left) CT scans will demonstrate erosion of one or both of the articular surfaces (Fig. 31, right). Osteitis pubis condition often co-occurs with osteomyelitis pubis, an infection of the pubic bone itself that presents similarly to osteitis pubis. A failure of conservative treatment for osteitis pubis typically implicates osteomyelitis pubis as the causative pathology. Osteomyelitis pubis, unlike osteitis pubis, is not self limiting and requires identification of the offending organism and treatment with the correct antibiotics. Knee Complex Introduction to the Knee The knee is the largest joint in the body. It consists of the tibiofemoral and patellofemoral joints contained within a single joint capsule. The proximal tibiofibular joint located on the lateral surface of the knee is also falls within this region, though it is not contained within the capsule. Motion at the knee occurs in two planes. Its primary actions are flexion and extension in the sagittal plane. The secondary actions of the knee complex are internal and external rotation in the transverse plane, physiological motions which typically occur in conjunction with movement at other joints in the lower extremity. Interactions between the hip, knee, and ankle allow for performance of many daily functional activities such as walking, running, standing, and sitting. The function of the knee is inextricably linked to that of the rest of the lower extremity due to the fact that approximately two thirds of the muscles crossing the knee also cross either the hip or the ankle. During the initial swing phase of gait, for example, knee flexion occurs passively in response to the active hip flexion and ankle dorsiflexion required to lift and clear the foot. In addition, muscles acting on the knee function in a primarily eccentric fashion. The knee extensors contract eccentrically during the loading response of gait in order to absorb the shock of heel contact and weight acceptance. The knee flexors eccentrically control passive extension of knee during terminal swing. The stability of the knee derives from the surrounding soft tissue like muscles and ligaments, rather than from its bony configuration. Without these soft-tissue restraints, the large
31 femoral condyles would not maintain sufficient contact with the nearly flat articular surfaces of the proximal tibia. However, during closed kinetic chain (CKC) activities when the foot is firmly planted, these vital restraints are at an increased risk for damage. Injury to these tissues reduces the stability of the joint and is the etiology of most common pathologies of the knee. Table 9: Muscles of the Knee Region Muscle Action Proximal Attachment Distal Attachment Segmental Innerva- tion Peripheral Innerva- tion Rectus femoris Extends knee; flexes hip Anterior inferior iliac spine & groove superior to the acetabulum The base of the patella L2, 3, 4 Femoral nerve Vastus intermedius Extends knee Anterior aspect of the proximal 2/3rds of the femoral shaft Lateral border of the patella L2, 3, 4 Femoral nerve Vastus lateralis Extends knee Intertrochanteri c line, greater trochanter, gluteal tuberosity and linea aspera Base and lateral border of the patella L2, 3, 4 Femoral nerve Vastus medialis Extends knee Intertrochanteri c line, spiral line, linea aspera and medial supracondylar line Base and medial border of the patella L2, 3, 4 Femoral nerve
32 Sartorius Flexes and assists medial rotation of the knee; flexes, abducts, and laterally rotates hip, and Anterior superior iliac spine Medial aspect of the proximal tibia (apart of the pes anserine) L2, 3, [4] Femoral nerve Tensor fasciae lata Assists in maintaining knee extension (via iliotibial band); abducts, flexes and medially rotates hip Anterior superior iliac spine and external lip of iliac crest Iliotibial band L4, L5, S1 Superior gluteal nerve Articularis Genu Pulls articular capsule proximally Distal anterior shaft of femur Proximal portion of synovial membrane of knee joint L2, 3, 4 Femoral Gracilis Flexes and medially rotates the knee; adducts hip Body of the pubis and inferior pubic ramus Medial surface of tibia, distal to condyle, proximal to insertion of semitendinosus , lateral to insertion of Sartorius (apart of the pes anserine) L2, 3, 4 Obturator
33 Gluteus Maximus Assists to stabilize the knee in extension (via iliotibial band) Aponeurosis of the erector spinae, sacrum, sacrotuberous ligament and posterior gluteal line of innominate Greater trochanter, gluteal tuberosity of the femur and iliotibial tract L5, S1, S2 Inferior gluteal nerve Semimem- branosus Flexes and medially rotates knee; extends hip Ischial tuberosity Posterior aspect of the medial tibial condyle L4, L5, S1, S2 Sciatic nerve (tibial division) Semitend- inosus Flexes and medially rotates knee; extends hip Ischial tuberosity Proximal, medial tibia L4, L5, S1, S2 Sciatic nerve (tibial division) Biceps Femoris: short head Flexes and laterally rotates knee Lateral lip of linea aspera and lateral supracondylar line Lateral side of the fibular head L5, S1, S2 Sciatic nerve (fibular division) Biceps Femoris: long head Flexes and laterally rotates knee; extends hip Ischial tuberosity and sacrotuberous ligament Lateral side of the fibular head L5, S1, S2, S3 Sciatic nerve (tibial division) Popliteus Flexes and medially rotates knee Lateral femoral condyle and oblique popliteal ligament Soleal line of the tibia L4, L5, S1 Tibial Gastroc- nemius Flexes knee; plantar Posterior aspect of the femoral condyles and Posterior calcaneal surface S1, S2 Tibial
34 flexes ankle joint capsule Plantaris Flexes knee; plantar flexes ankle Lateral supracondylar line Posterior calcaneal surface L4, L5, S1, S2 Tibial Neurovascular Supply to the Knee The popliteal artery is the main source of blood supply to the knee. It is a continuation of the femoral artery, which becomes the popliteal artery after passing through the adductor hiatus, an opening in the adductor magnus muscle just superior to the femoral epicondyles. The popliteal artery then dives deep within the popliteal fossa, coursing along the surface of the joint capsule until it reaches the inferior border of the popliteus muscle. At this point, the popliteal artery bifurcates into posterior and anterior tibial arteries. Immediately superior to this bifurcation, the popliteal artery gives off five genicular branches which anastomose around the tibiofemoral and patellofemoral joints. These branches include the following: ● Superior lateral and superior medial genicular arteries, which encircle the femoral condyles and the superior patella ● Middle genicular artery, which supplies the anterior and posterior cruciate ligaments ● Inferior lateral and inferior medial genicular arteries, which encircle the tibial condyles and inferior patella. This bundle of arteries is referred to as the genicular anastomosis (Fig. 32). The descending branch of the lateral circumflex femoral artery and the descending genicular artery both run anterior to the knee. Just superior to the patella, they join an anastomosis with the superior genicular arteries (medial and lateral). Just inferior to the patella, the inferior lateral and inferior medial genicular arteries anastomosis with the superior lateral and superior medial genicular arteries, respectfully. The final two branches of the genicular anastomosis are the Figure 32: Genicular Anastomosis anterior and posterior tibial recurrent arteries, which ascend from the anterior tibial artery to contribute the vascular supply of the knee. The anastomotic arrangement of these arteries is crucial to ensuring that the knee joint maintains continuous blood supply regardless of its position. When the knee is fully flexed, for example, the popliteal artery can become compressed
35 Figure 33: Cutaneous Nerve Distribution of the Lower Extremity within the popliteal fossa, leading to an interruption of its blood flow. However, the anastomoses around the knee ensure that oxygenated blood continues to supply the joint despite the temporary obstruction of the popliteal artery. The sciatic nerve provides the innervation of the knee joint and surrounding tissues. Immediately superior to the popliteal fossa, the sciatic nerve bifurcates into the tibial nerve and the common fibular nerve; these peripheral nerves contain fibers from the anterior and posterior divisions of the sacral plexus, respectively. Just proximal to this bifurcation, the sciatic nerve gives off multiple muscular branches which supply the hamstrings. The tibial nerve is the larger component of the bifurcated sciatic nerve. It descends inferiorly through the popliteal fossa, running with the popliteal vessels. The tibial nerve gives off branches to innervate the muscles that attach proximally to the posterior knee. Immediately superior to the two heads of the gastrocnemius muscle, the tibial nerve gives rise to the medial sural cutaneous nerve, which courses superficially over the lateral head of the gastrocnemius to supply the skin of the posterolateral leg. The common fibular nerve courses parallel to the distal portion of the biceps femoris muscle. Echoing the branching of the tibial nerve, the common fibular nerve gives off the lateral sural cutaneous nerve immediately superior to the proximal attachments of the gastrocnemius muscle. This nerve descends along the posterolateral aspect of the gastrocnemius to supply the skin of the posterolateral surface of the proximal leg. The common fibular nerve continues inferiorly down the leg, traveling along the posterolateral aspect to curve around the fibular head, where it then bifurcates into superficial and deep fibular branches. Both of these nerves descend along the lateral aspect of the tibia , with the deep fibular nerve staying closer to the tibia and the superficial nerve approximating closer to the skin. Both branches ultimately ramify in dorsum of the foot. At the approximate midpoint of the posterior leg, the medial and lateral sural cutaneous nerves join to form the sural nerve. The sural nerve innervates the skin on the posterolateral aspect of the leg and foot. The femoral nerve and its branches are the main source of innervation to the anterior lower limb. While the femoral nerve gives off branches to the muscles of the anterior thigh (e.g., the quadriceps and the sartorius) and provides cutaneous sensation to the anteromedial thigh, most of its motor fibers have actually terminated by the time it reaches the knee. Therefore, most of the anterior knee nerve supply is cutaneous providing sensory innervation.
36 The anterior femoral cutaneous branches supply the skin of the anteromedial thigh and knee; similarly, the lateral femoral cutaneous branches supply the skin of the anterolateral thigh and knee. While most of the cutaneous branches from the femoral nerve are restricted to the anterior surface of the lower extremity, the femoral nerve provides a few posterior femoral cutaneous branches, which supply the skin over the popliteal fossa. The saphenous nerve is the terminal branch of the femoral nerve; it provides cutaneous sensation to the skin of the inferior anteromedial knee. The cutaneous nerve distribution and the dermatomes of the lower extremity vary, but they generally comprise L2 – L5 anteriorly and S1 and S2 posteriorly (Fig. 33). Tissue Layers of the Knee Region (Superficial to Deep) ● Epidermis ● Dermis ● Adipose ● Fascia ○ Tensor fascia lata ■ Iliotibial band ■ Intermuscular septa ○ Medial and lateral patellar retinaculum ● Muscle and Tendons ○ Sartorius ○ Rectus femoris ○ Vastus lateralis ○ Vastus medialis ○ Patellar tendon ○ Gracilis ○ Biceps femoris ○ Semimembranosus ○ Semitendinosus ○ Gastrocnemius ○ Plantaris ○ Popliteus ● Bursa ○ Prepatellar ○ Infrapatellar ○ Deep infrapatellar ○ Suprapatellar ○ Subpopliteal ○ Pes anserine ● Neurovasculature ○ Common fibular nerve ■ Lateral sural cutaneous nerve
37 ○ Tibial nerve ■ Medial sural cutaneous nerve ○ Sural nerve ○ Popliteal artery ■ Superior medial genicular a. ■ Superior lateral genicular a. ■ Middle genicular a. ■ Inferior medial genicular a. ■ Inferior lateral genicular a. ● Extracapsular and capsular ligaments ○ Lateral collateral ligament (LCL) ○ Anterolateral ligament (ALL) ○ Medial collateral ligament (MCL) ■ Superficial and deep ● Joint capsule ○ Fibrous capsule ○ Synovial membrane ○ Articular cartilage ■ Femoral condyles ■ Tibial plateau ○ Menisci ■ Medial ■ Lateral ○ Intracapsular ligaments ■ Anterior cruciate ligament (ACL) ■ Posterior cruciate ligament (PCL) ○ Synovial fluid The Tibiofemoral Joint The tibiofemoral joint is formed by the articulation between the convex femoral condyles (medial and lateral) and the primarily flat surfaces of the tibial condyles. The large femoral condyles provide significant surface area for articulation with the tibia; this permits a large range of motion in the sagittal plane and is important for performance of dynamic, lower extremity- driven activities like running, biking, and climbing. The consequence of a large range of motion, however, is a reduction in overall joint stability: the intra-articular space of the tibiofemoral joint is rather wide and loose, so stability is provided by the menisci, the knee ligaments and joint capsule, the surrounding musculature, and the compressive force of gravity (i.e., body weight). Table 10: Physiologic Motions of the Tibiofemoral Joint and the Associated Muscles
38 Motion Primary Associated Muscles Secondary Associated Muscles Knee Flexion Hamstrings (long head and short head of the biceps femoris, semimembranosus, semitendinosus) Gastrocnemius, gracilis, plantaris, sartorius, popliteus Knee Extension Quadriceps (rectus femoris, vastus lateralis, vastus medialis, vastus intermedius) Tensor fascia lata Knee Internal Rotation Semimembranosus, semitendinosus Gracilis, sartorius Knee External Rotation Biceps femoris N/A Biomechanics and Kinematics of the Tibiofemoral Joint The bony structure of the tibiofemoral joint is distinct in both its anterior and posterior aspects. Anteriorly, the medial and lateral femoral condyles are covered by articular cartilage. Between the condyles lies the shallow intercondylar groove, which articulates with the posterior surface of the patella (discussed in detail below: see “The Patellofemoral Joint”). Posteriorly, there is still articular cartilage, but there is a deep intercondylar fossa that lies between the medial and lateral femoral condyles; the cruciate ligaments intersect within this fossa. Due to the angle of inclination of the femur (125 degrees in a typical adult), the femoral shaft deviates medially towards midline. In order to establish a vertical orientation of the tibia, the tibiofemoral joint exhibits a lateral angle of approximately 170 to 175 degrees (Fig. 34). This normal alignment creates a slight genu valgus, or “knock-knee”, positioning at the joint. Variations in the degree of this lateral angle are common and can lead to excessive genu valgum (a lateral angle less than 165 degrees) or genu varum, or “bow-leg”, (a lateral angle greater than 180 degrees), as depicted in Figure 34B. A measurement technique known as the Q (for “quadriceps”) angle can quantify these positions and objectively describe the alignment of the knee in the context of the entire lower extremity.
39 Figure 34: Angle of Inclination of the Femur The Q angle is formed at the intersection of a line visually drawn from the anterior superior iliac spine (ASIS) to the midline of the patella, and a line from the patellar midline to the tibial tuberosity. The tibiofemoral joint is classified as a synovial, bicondylar joint with two degrees of freedom. Its primary motions are flexion and extension in the sagittal plane. When the knee is slightly flexed, slight axial (internal and external) rotation may occur in the transverse plane. The femoral condyles are not perfectly rounded; these asymmetrical articular surfaces cause the medial-lateral rotatory axis to vary as the knee flexes through its available range. The range of motion available in these two planes can vary, especially with age and gender. However, typical motion in the sagittal plane ranges from 130 – 150 degrees of flexion to 0 – -5 degrees of extension (this implies that an individual presenting with 5 degrees of hyperextension falls within the range of normal). Range of motion in the transverse plane depends upon the degree of knee flexion. If the knee is flexed to 90 degrees, total axial rotation is typically 40 to 45 degrees. Range of motion into external rotation is generally double that of internal rotation. When the knee is fully extended (to 0 degrees), axial rotation is restricted. As the knee moves from flexion into extension, external rotation serves to “lock” the joint into full extension. This position of full knee extension with external rotation is the closed-packed position of the knee, indicating maximal bony congruency between the femoral condyles and the tibial plateau. This mechanism will be discussed further in the “Joint Configuration” section below. The tibiofemoral joint capsule is large and lax to allow for the extensive range of motion required during many functional and recreational activities. The capsule also contains synovial fluid, which facilitates smooth movement of the tibiofemoral joint. Despite its relative laxity, however, the capsule does provide some restraint of motion in all various directions. The capsule is composed of a superficial fibrous layer and a deep synovial membrane. The fibrous layer is continuous with the iliotibial band, the extensor retinaculum of the ankle, and some ligaments of the knee. The capsule also supplies proprioceptive input and pain signals to the central nervous system via its intrinsic mechanoreceptors and nociceptors. The muscles that cross the tibiofemoral joint provide additional support and restraint of motion: for example, the pes anserine group, composed of the sartorius, the gracilis, and the semitendinosus muscles, resists external rotation and valgus forces at the knee. Many muscles act on the knee to provide movement in the sagittal and transverse planes. A single muscle group, the quadriceps femoris, is responsible for knee extension: it includes the rectus femoris and the vastii (lateralis, medialis, and intermedius) muscles. The vastii provide approximately 80% of knee extension torque, while the rectus femoris provides the remaining 20% and is critical to achieving full knee extension. Since the rectus femoris crosses the hip joint via its proximal attachment at the anterior superior iliac spine, it also contributes to hip flexion; this actions assists movement of the limb through the swing phase of the gait cycle. The vastus lateralis has the largest cross-sectional area of the quadriceps muscles, affecting the lateral
40 pull of the patellofemoral joint (further discussed in the “Patellofemoral Joint” section). In addition, the oblique fibers of the vastus medialis and lateralis create a force upon the patella. In order for the patella to glide smoothly and stably within the intercondylar groove, each of these two vastii must directly counteract the pull of the other. The vastus intermedius works in synergy with the other quadriceps muscles to draw the joint capsule superiorly as the knee extends (these biomechanics are discussed further in “The Patellofemoral Joint”, below). The muscles that cross the posterior knee generate movement into flexion and axial rotation. The gastrocnemius and plantaris muscles produce pure knee flexion without a rotatory component. The biceps femoris is the only muscle that can flex and externally rotate the knee. The remaining muscles flex and internally rotate the knee to varying degrees. Although the biceps femoris must counteract the pull of several internal rotators, its moment arm for rotation is longer than those of the internal rotators: its distal attachment on the fibular head increases the distance between the muscle fibers and the the axis of rotation, particularly when the knee is flexed to 90 degrees. Consequently, the biceps femoris alone can provide the enough torque into external rotation to counterbalance the internal rotators and maintain the knee in a position of neutral rotation. The knee extensors provide approximately 66% more torque than the knee flexors. The extensors produce maximal torque when the knee is positioned in 45 – 70 degrees of flexion; significantly less torque is produced at either extreme of flexion or extension. These variations in extension torque stem from changes in muscle and moment arm lengths throughout the joint’s range of motion; patellar movement and axial rotation of the tibiofemoral joint also impact the extension torque available at any given location in the arc of motion. Maximal knee flexion torque occurs when the joint is flexed between 0 – 20 degrees. Although the moment arm for the hamstring group is greatest when the knee is flexed from 50 – 90 degrees, the length-tension relationships of these muscles play an important role in determining the position of maximal torque production. With exception of the short head of the biceps femoris, the hamstrings are all two-joint muscles; therefore, the concomitant degree of hip flexion directly affects the length- tension relationship of the hamstrings and thus their ability to produce a flexion moment at the knee. For example, hip flexion elongates the hamstrings at their proximal attachment, allowing for increased production of flexion torque at the knee; hip extension has the opposite effect. During closed kinetic chain movements (i.e., any movement in which the foot is fixed in a weight bearing position), the external demand moment at the knee is greatest when the knee is flexed to 90 degrees; external demand decreases as the knee extends. Functionally we would have to exert less quadriceps force (to extend the knee and stand up) compared to squatting down. However, during open kinetic chain, or non-weight bearing, movements, the external demand moment is greatest when the knee is extended to 0 degrees; it decreases as the knee is flexed (Fig. 35). In a functional context, this relationship means that sitting in a chair with the knees in varying degrees of flexion (Fig. 35A-B) will require less extensor (quadriceps) activity than would be required to maintain terminal knee extension in the seated position (Fig. 35C).
41 Figure 35: Open Chain Knee Extension Ligaments of the Tibiofemoral Joint The two intra-articular cruciate ligaments of the tibiofemoral joint intersect within the intercondylar space, forming the cross shape that gives them their name. Each is named based on the location of its attachment to the articular surface of the tibia. Thus, the anterior cruciate ligament (ACL) attaches to the anterior surface of the tibial plateau and the posterior cruciate ligament (PCL) attaches to the posterior surface of the plateau (Fig. 36). They both rely on vasculature within the synovial membrane for their blood supply. The cruciate ligaments are thick, strong structures that provide a significant amount of stability to the tibiofemoral joint by resisting shear forces in the sagittal plane. The cruciates also contain mechanoreceptors, which provide the central nervous system (CNS) with proprioceptive feedback regarding the position of the knee joint.
42 Figure 37: Anterior Slide of Tibia on Femur The anterior cruciate ligament functions primarily to prevent anterior shear of the tibia on the femur, as may occur when the knee approaches full extension in the open kinetic chain (Fig. 37). The knee moves into the final 50 – 60 degrees of open-chain knee extension, the contraction of the quadriceps pulls the tibia anteriorly on the femur. When the ACL becomes taut in this position, thereby limiting the extent of this anterior slide. The quadriceps muscle is often referred to as the “ACL antagonist”, since it directly opposes the ACL’s restraint of anterior tibial glide. In order to determine if the ACL is lax or ruptured following on injury, clinicians may perform the anterior drawer test (along with other special tests): with the knee flexed to 90 degrees and the foot fixed, the clinician applies a direct, firm, posterior-to-anterior force to the tibia. If anterior translation of the tibia on the femur is increased relative to the uninvolved knee, this result is highly suggestive of an ACL tear. The ACL is most taut in a position of terminal knee extension, as shown in Figure 39B; this allows the ACL to stabilize the knee during weight-bearing activities in which the knee is relatively extended. However, some fibers of the ACL are taut at any given point in the arc of motion. This property of the ligament arises from its unique double-bundle configuration: the ACL is formed from two distinct fiber groupings, the anteromedial and posterolateral bundles, which are named according to their tibial attachments. These bundles have different fiber orientations and therefore different lines of pull, which permits the ACL to resist anterior tibial translation throughout knee extension. Additionally, the oblique orientation of the entire ACL unit enables it to resist axial rotation and valgus forces. The PCL also has two primary fiber groups, the anterolateral and posteromedial bundles. The PCL is most taut in a position of 90 – 120 degrees of knee flexion, but, as in the ACL, the opposing orientation of these bundles allows some fibers to remain taut throughout both flexion (the anterolateral bundle) and extension (the posteromedial bundle). The oblique orientation of the PCL unit also allows it to resist tibial rotation and both varus and valgus loads. Figure 36: Ligamentous Structures of the Knee
43 Figure 39: Intra-articular Ligaments of the Tibiofemoral Joint, on slack (A) and under tension (B) Figure 38: Posterior Slide of Tibia on Femur The primary role of the posterior cruciate ligament is to limit posterior shear of the tibia on the femur, as occurs as the knee approaches full flexion in the open kinetic chain (Fig. 38). As knee moves into 90 degrees of flexion, the contraction of the hamstrings pulls the tibia posteriorly on the femur. As the PCL becomes taut, it helps limit the extent of this posterior slide. Much like the quadriceps, the hamstring muscles are often referred to as the “PCL antagonist”, as they directly oppose the PCL’s restraint of posterior tibial glide. The posterior drawer test allows clinicians to assess the integrity of the PCL. This test is identical to the anterior drawer, with the obvious exception that the force applied to the tibia is directed from anterior to posterior. The collateral ligaments are broad, thick structures running along the medial and lateral aspects of the knee. The medial collateral ligament (MCL) consists of superficial and deep parts divided by a bursa (Fig. 36). The superficial portion of the MCL is most taut when the knee is extended (Fig. 39B), and it functions primarily to resist valgus forces. The deep portion is continuous with the joint capsule and is secured to the medial meniscus; it does not play a significant role in resisting valgus forces at the knee. When the knee is fully extended, the capsule, pes anserine, and the ACL also contribute to the resistance of valgus forces applied to the extended knee. When the knee is flexed to 20 – 30 degrees, these structures become less involved, making the MCL the primary resistance to help limit valgus force. The MCL also works in synergy with the ACL to limit anterior shearing of the tibia on the femur. If the MCL is ruptured, however, the ACL becomes the only ligament resisting anterior shear, and is therefore subjected to increased stress. Fortunately, unlike the cruciate ligaments, MCL has a robust blood supply and is much more likely to heal on its own.
44 Fig. 40: Extracapsular Ligaments of the Lateral Knee The lateral collateral ligament (LCL) is a strong, round band; its distal portion blends with the biceps femoris tendon. It is an extracapsular structure, and unlike the MCL, it does not attach directly to its corresponding (lateral) meniscus. The LCL primarily resists varus forces at the knee. Similar to the MCL, the LCL is most taut in extension, due to its position slightly posterior to the medial-lateral axis of the knee. However, the LCL fulfills its primary function (as the principle resistor of varus force) when the knee is slightly flexed. In addition to the extracapsular collateral ligaments, the anterolateral ligament (ALL) has recently been recognized as an independent extracapsular ligament of the knee. Its proximal attachment lies near that of the LCL, but it attaches distally to the anterolateral surface of the tibial plateau (Fig. 40). Its primary role is to provide rotational stability; therefore, damage to the ALL places the knee at increased risk for injury during rotatory movements. The ALL also resists varus forces at the knee, and it is most taut in extension. The two menisci of the tibiofemoral joint are attached to the tibial plateau. The medial and lateral menisci are crescent-shaped, fibrocartilaginous structures that form shallow “seats” for the large convex femoral condyles, thus stabilizing their articulation with the tibial plateau. This soft tissue adaptation is most important at the lateral tibial condyle due to the slightly convex shape of this articular surface. The anterior and posterior horns of the menisci anchor them to the intercondylar region of the tibia. A slender transverse ligament joins the medial and lateral menisci anteriorly. The coronary ligaments connect the external edge of each meniscus to the medial and lateral surfaces of the tibial plateau; they are relatively loose to allow for rotatory motion at the knee. Various muscles also attach to the menisci to help stabilize them during joint motion. For instance, the quadriceps and semimembranosus muscles attach to both menisci; the popliteus muscles attaches to only the lateral meniscus. As stated previously, the medial meniscus attaches directly to the MCL, whereas the external border of the lateral meniscus attaches to the lateral joint capsule. Capillaries within the synovial membrane supply the outer two-thirds of the menisci. The blood supply diminishes significantly as it travels deep into the
45 Fig. 41: Menisci of the Tibiofemoral Joint joint space; consequently, the inner one-third of each meniscus is functionally avascular which prevents the healing process. The primary function of the menisci is to reduce compressive forces within the tibiofemoral joint by dispersing the forces over a larger surface area. This is a critical function for preserving joint health, as these compressive forces average 2.5 – 3 times the force of body weight during ambulation; they increase to almost 4 times body weight while ascending stairs. Studies have shown that a complete lateral meniscectomy increases the contact pressures within the tibiofemoral joint by 230 percent. This intensification of intra-articular pressure ultimately increases an individual’s risk for developing stress-related arthritis and significant knee pain. Even an incomplete tear in either meniscus leads to an increase in local stress and wear on the articular cartilage. The menisci are therefore integral to the health and longevity of the tibiofemoral joint. Other secondary functions of the menisci include providing the CNS with proprioceptive feedback, stabilizing the joint during motion, lubricating the articular cartilage, and guiding the arthrokinematics of the knee. The O-shaped lateral meniscus covers a larger area of the tibial plateau than does the C-shaped medial meniscus (Fig. 41). However, the majority of compressive forces act upon the medial compartment of the knee, placing greater stress on the medial joint surface and meniscus. The lateral meniscus is less strongly adhered to the tibial plateau and is therefore more mobile than its medial counterpart. Joint Configuration of the Tibiofemoral Joint The femoral condyles are convex surfaces and the tibial plateau is primarily concave. As stated above, the lateral tibial plateau is slightly convex, but the lateral meniscus creates a concave surface to allow the lateral femoral condyle can move more smoothly. During weight bearing (closed-chain) activities, the convex femoral condyles move on the concave tibial plateau. During non-weight bearing (open-chain activities), the concave tibial plateau moves on the convex femoral condyles. Tibiofemoral arthrokinematics in the sagittal plane occur via rolls and glides. As the knee moves into extension during closed chain activity, the femur rolls anteriorly and glides posteriorly to fit onto the tibial plateau. Conversely, as the knee moves to flexion during closed chain activity, the femur rolls posteriorly and glides anteriorly. In open chain extension, the tibia rolls anteriorly and glides anteriorly to properly articulate with the femoral condyles. In open
46 Fig. 42: Tibiofemoral Arthrokinematics in the Open (A) and Closed (B) Chains chain flexion, the tibia rolls and glides posteriorly. These interactions are illustrated in Figure 42. Arthrokinematics in the transverse plane occur via spinning (axial rotation) of the moving articular surface on the stable surface. In the open chain, external rotation of the knee occurs via external rotation of the tibia on the femur and internal rotation of the knee is driven by internal rotation of the tibia on the femur. Thus, the relationship between tibial and total knee rotation is direct. The reverse occurs in the closed chain: external rotation of the knee occurs by internal rotation of the femur on the tibia and internal rotation of the knee occurs by external rotation of the femur on the tibia. This represents an indirect relationship between femoral and total knee rotation. As noted earlier, axial rotation is only available when the knee is in some flexion; rotational range of motion increases with greater knee flexion. Apparently similar to, through functionally different from axial rotation in the transverse plane, the “screw-home” mechanism describes the rotation of the tibiofemoral joint that occurs during the last 30 degrees of extension in order to “lock” the joint into place/ Screw-home rotation is a conjunct movement that cannot be performed independently of physiologic flexion and extension. This mechanism can occur during both open and closed chain activities. In non-weight bearing positions, the tibia externally rotates on the femur to “lock” the knee in terminal extension and must internally rotate to “unlock” the tibia towards flexion. While weight-bearing, the femur must internally rotate on the tibia to “lock” the knee in terminal extension and must externally rotate to “unlock” the femur into flexion. The screw-home mechanism can be affected by the following three factors: the shape of the medial femoral condyle, the passive tension in the ACL, and the lateral pull of the quadriceps muscle. The shape of the medial femoral condyle affects the screw-home mechanism the most significantly. The medial femoral condyle extends further anteriorly than does the lateral femoral condyle; therefore, the moving tibia must curve around this projection. As the femur rolls anteriorly and glides posteriorly during closed chain extension, it deviates medially, thus internally rotating on the stable tibia to create the “locking” mechanism. During open chain extension, as the tibia rolls and glides anteriorly, it deviates slightly lateral to the medial femoral condyle, thereby externally rotating on the stable femur in order to “lock”. To “unlock” the knee, the articular surfaces of the tibia must glide back to their neutral alignment in the intercondylar
47 groove. The popliteus muscle also assists in “unlocking” the knee: its muscle action opposes the screw-home mechanism. Table 11: Ligaments of the Tibiofemoral Joint Ligament Proximal attachment Distal attachment Function Associated constraints of tibiofemoral joint Anterior cruciate (ACL) Medial side of lateral femoral condyle Anterior intercondylar area of tibia Stabilization in the sagittal and transverse planes Open chain: anterior translation of tibia on femur Closed chain: posterior translation of femur on tibia Knee extension Extreme axial rotation Extreme varus/valgus force Posterior cruciate (PCL) Lateral side of medial femoral condyle Posterior intercondylar area of tibia Stabilization in the sagittal plane Open chain: posterior translation of tibia on femur Closed chain: anterior translation of femur on tibia Knee flexion Extreme axial rotation Extreme varus/valgus force Medial collateral (MCL) (see below) (see below) Limits valgus force Stabilization of knee, especially in extension and end-range Valgus force Knee extension End-range axial rotation (external rotation)
48 external rotation MCL superficial Medial epicondyle of femur Medial-proximal part of tibia More rotational force (external rotation) Tibial external rotation MCL deep Deep, posterior, and distal to superficial fibers Posterior-medial joint capsule, semimembranos us tendon, medial meniscus More valgus force Genu valgum Lateral collateral (LCL) Lateral epicondyle of femur Head of fibula Stabilization of the lateral knee Varus force Knee extension End-range axial rotation Anterolatera l (ALL) Proximal and posterior to lateral femoral epicondyle Lateral tibial plateau between head of fibula and Gerdy’s tubercle Taut with knee extension (0-60 degrees) and internal rotation Varus force Transverse Connects the medial and lateral menisci Posterior Oblique Posterior to adductor tubercle and anterior to gastrocnemius tubercle on femur Distal and posterior to distal attachment of superficial MCL on tibia Reinforces posterior capsule, especially posteromedial corner Oblique popliteal Adjacent to postero- superior area of lateral femoral Posteromedial capsule and semimembranos us tendon Reinforces posterior capsule, especially posteromedial Knee external rotation
49 condyle corner Arcuate popliteal Two heads: 1. Posterior intercondylar area of tibia 2. Posterior side of lateral femoral condyle Fibular head Reinforces posterior capsule, especially posterolateral corner Coronary External edges of menisci Tibial edge and nearby capsule Attaches the menisci to the tibia Meniscofem oral May assist stabilization of the lateral meniscus of posterior horn · Meniscofem oral posterior Femur posteromedial to PCL Lateral meniscus posterior horn · Meniscofem oral anterior Femur anterior to PCL Lateral meniscus posterior horn Common Tibiofemoral Joint Pathology The ACL is the most commonly torn ligament tear of the knee. ACL ruptures are much more common in females compared to males primarily due to the anatomical structure of the female pelvis and lower extremity: females typically have a wider pelvis, a larger Q-angle, increased range into knee extension, a narrower femoral notch, and less developed thigh musculature, all of which increase susceptibility to ACL injury. An ACL tear occurs when the tibia is displaced anteriorly on the femur to such an extreme that tensile stress on the ACL exceeds the capacity to resist. Common mechanisms of injury include a non-contact rotational force at the knee, hyperextension, poor biomechanics when landing a jump, or a direct blow to the lateral side of the knee which generates a valgus stress. The ACL is rarely injured in open-
50 Figure 43: Osteoarthritis of the Knee chain movements. Often times the patient will report hearing a “pop” or state that the knee “gave way” at the time of injury, and describe onset of swelling immediately after the event. Many ACL injuries also involve damage of other local structures, including the MCL, the menisci, and the knee joint capsule. Since the ACL is an intracapsular structure and does not heal well independently, ruptures are often treated surgically by using autographs of the patient’s patellar or hamstring tendon or cadaveric allografts to replace the native ACL. Meniscal tears are also quite common. They can be classified as acute (sudden onset), chronic (typically in patients older than 50 years of age with no specific injurious event to report), or degenerative (associated with arthritis). Common mechanisms of injury include forced axial rotation or an external valgus force (such as occurs in a blow to the lateral aspect of the knee) in closed-chain movements. The individual may report hearing a “pop” and a slow onset of effusion; these patients often present with tenderness to palpation along the joint line. The location of the tear can help determine the patient’s prognosis. The the outer 1/3 of the meniscus (the “red-red zone”) receives substantial blood supply. A tear in the red-red zone has the best prognosis and a good potential for healing. If the tear is in the middle 1/3 of the meniscus (the “red- white zone”), the prognosis is more guarded, though there may be some healing potential due to moderate blood supply to this area. The white-white zone is the inner 1/3 of the meniscus and does not receive any blood supply: a tear in this zone has the worst prognosis and is unlikely heal. Meniscal tears may benefit from conservative management including a temporary change in activity and use of NSAIDs for control of inflammation. If the meniscus does not heal and swelling and pain still persist after one month of conservative management, the individual may need surgery. Surgery can consist of a partial or complete meniscectomy; however, meniscectomies are no longer recommended due to the risk of developing osteoarthritis. Another option for surgery could be a meniscal repair for a tear in the red-red zone. Osteoarthritis of the knee occurs when there is decreased intra-articular space between the femur and tibia. This typically occurs when the menisci are progressively worn or when there is eroding of the articular cartilage of the femoral condyles. Both situations lead to bone-on-bone contact, which can result in the formation of bone spurs (Fig. 43). The elderly are more prone to this progressive degenerative joint disease. Other factors that can lead to osteoarthritis include increased weight bearing through the meniscus (as in cases of obesity), a previous injury to the tibiofemoral joint, or inappropriate loading through the joint due to genu varus or valgus position. Common complaints from individuals with osteoarthritis include pain, morning stiffness, and/or difficulty fully flexing or extending the knee secondary to stiffness or edema.
51 Management of osteoarthritis can vary, but the most common final treatment is a total knee arthroplasty to replace the joint surfaces with metal or plastic. The Patellofemoral Joint The patellofemoral joint is formed by the articulation of the patella, the largest sesamoid bone in the body, with the intercondylar groove of the femur. The patella is embedded within the quadriceps tendon and attaches to the tibial tuberosity of the tibia. Neurovascular supply to this joint was described previously. Stability of the joint is provided by the quadriceps muscles, the structure of the joint surfaces, and the surrounding retinacular fibers of the joint capsule. Table 12: Physiologic Motions of the Patellofemoral Joint and the Associated Muscles Motion Primary Associated Muscles Secondary Associated Muscles Superior Glide (associated with knee extension) Quadriceps (rectus femoris, vastus lateralis, vastus medialis, vastus intermedius) N/A Inferior Glide (associated with knee flexion) Eccentric motion of the quadriceps Hamstrings (biceps femoris, semimembranosus, semitendinosus) Biomechanics and Kinematics of the Patellofemoral Joint The biomechanics and kinematics of the patellofemoral joint vary throughout flexion and extension of the knee. At rest, the patella lies slightly inferior to the suprapatellar fat pad. When the knee is flexed to approximately 135 degrees, the superior pole of the patella is the primary point of contact with the femur. As the knee extends to a 90 degree angle, this primary contact point begins to migrate inferiorly. While the surface area of contact between the patella and femur is the largest in this position, the total contact area still only involves one-third of the posterior patellar surface. At 20 degrees of knee flexion, the inferior pole of the patella is its primary point of contact with the femur; the patella now articulates only very slightly with the intercondylar groove of the femur. The black circle in each panel of Figure 44 illustrates the point of maximal contact between the patella and the femur in each of these positions. The
52 Figure 44: Biomechanics of the PatellaFigure 45: Forces Acting on the Patella patella is most stable within the intercondylar groove of the femur when the knee is flexed between 60 - 90 degrees. When the knee is in full extension (and the quadriceps are relaxed), the patella can be moved freely relative to the femur. Since the patella is imperfectly congruent with the femur, it requires many other structures to maintain stability. One of the primary stabilizers is the quadriceps muscle group, which also significantly influences the tracking of the patella. During knee extension, the contraction of the quadriceps muscle primarily pulls the patella superiorly, then slightly laterally and posteriorly into the intercondylar groove. The iliotibial band and lateral patellar retinacular fibers supplement this lateral pull on the patella (Figure 45). To quantify the amount of lateral pull on the patella, a Q-angle can be measured. Activation of the oblique fibers of the vastus medialis and the medial patellar retinacular fibers help counteract this pull. The medial patellar retinacular fibers contain the medial patellofemoral ligament: this ligament forms the thickest portion of the retinaculum and provides the strongest restraint against the lateral pull of the quadriceps. Even though all of these muscles and ligaments have a significant impact on patellar biomechanics, the most crucial resistance to the lateral pull itself is the lateral femoral condyle itself. The slope of the lateral condyle is steeper than that of the medial condyle, allowing to promote proper patellar tracking within the groove. Individuals with a small lateral femoral condyle and a shallow intercondylar groove are more susceptible to patellar dislocation and/or subluxation.
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LE arthrology guide

  • 1. Arthrology Guide to the Joints of the Lower Extremity Clinical Anatomy II, Summer 2015 Table 15 Sarah Burkhardt, Trey Downey, Steven Hennig, Sam Jensen, Danielle Meier, Jamie Parsons, Kristen Sanchez, Caitlyn Tivy Table of Contents
  • 2. 1 Hip Complex……………………………………………………………………………...p. 2 Femoroacetabular Joint…………………………………………………………...p. 7 Sacroiliac Joint……………………………………………………………………p. 21 Pubic Symphysis………………………………………………………………….p. 28 Knee Complex…………………………………………………………………………….p. 32 Tibiofemoral Joint………………………………………………………………...p. 39 Patellofemoral Joint………………………………………………………………p. 53 Proximal Tibiofibular Joint……………………………………………………….p. 58 Ankle and Foot Complex………………………………………………………………….p. 62 Distal Tibiofibular Joint…………………………………………………………..p. 62 Talocrural Joint…………………………………………………………………...p. 68 Subtalar Joint……………………………………………………………………..p. 76 Transverse Tarsal Joint…………………………………………………………...p.85 Talonavicular Joint Calcaneocuboid Joint Cuneonavicular Joint……………………………………………………………...p. 94 Cuboideonavicular Joint…………………………………………………………..p. 101 Intercuneiform and Cuneocuboid Complex………………………………………p. 107 Tarsometatarsal Joints…………………………………………………………….p. 113 Intermetatarsal Joints……………………………………………………………..p. 121 Metatarsophalangeal Joints……………………………………………………….p. 125 Interphalangeal Joints of the Foot………………………………………………...p. 133 References…………………………………………………………………………………p. 140 Hip Complex The hip region, or pelvic girdle (Fig. 1), consists of the femoroacetabular (hip) joints, the sacroiliac joints and the pubic symphysis, which work together to serve as the connection between the
  • 3. 2 Fig. 1: The pelvic girdle, posterior view trunk and the lower extremities. The two halves of the pelvic ring are formed by the innominate bones; each innominate is a fusion of three smaller bones: the ilium, the ischium, and the pubis. These halves join anteriorly at the pubic symphysis and posteriorly at the bilateral sacroiliac joints; the pelvis connects to the lower limbs via the hip joints. The location and structure of these joints in the mature skeleton are influenced by weight-bearing activities: the pelvis functions to transfer forces from the trunk to the lower extremities as well as from the ground into the axial skeleton. The three joints of the pelvis are innervated by branches of the lumbar and sacral plexuses and receive their blood supply from branches of the internal and external iliac arteries. The following sections describe the arthrology of these joints and the muscles acting on each. Table 1: Muscles of the Hip Region Muscles Proximal Attachment Distal Attachment Innervation Action Muscles of the Back Erector Spinae Sacrum, iliac crest, spinous processes L5- T11, supraspinous ligament Angles of ribs to costal angles Dorsal rami of the spinal nerves Extension & lateral flexion of the vertebral column Multifidus (transversos pinalis) Sacrum, posterior SI ligament, posterior iliac spine, transverse processes More superior spinous processes Dorsal rami of the spinal nerves Extension & contralateral rotation of the vertebral column Latissimus Dorsi Spinous processes of inferior 6 thoracic vertebrae, thoracolumbar fascia, iliac crest, and inferior 3-4 ribs Floor of intertubercular sulcus of humerus Thoracodorsal nerve (C6,C7,C8) Extends, adducts, and medially rotates humerus; raises body toward arms during climbing Abdominal Muscles- Anterior Wall
  • 4. 3 External Oblique External surfaces of 5th - 12th ribs Linea alba, pubic tubercle, anterior half of iliac crest Thoracoabdo minal nerves (T7-T11) and subcostal nerve Flexes and rotates trunk Internal Oblique Thoracolumbar fascia, anterior ⅔ of iliac crest, and connective tissue deep to lateral third of inguinal ligament Linea alba with aponeurosis of internal oblique, pubic crest, and pecten pubis via conjoint tendon Thoracoabdo minal nerves (ant. rami of T6-T12) and first lumbar nerves Compresses and supports abdominal viscera Rectus Abdominis Pubic symphysis and pubic crest Xiphoid process and 5th - 7th costal cartilages Thoracoabdo minal nerves (ventral rami of T6 - T12) Flexes trunk and compresses abdominal viscera; stabilizes and controls tilt of pelvis Transversus Abdominus Internal surfaces of 7th - 12th costal cartilages, thoracolumbar fascia, iliac crest, and deep to lateral third of inguinal ligament Linea alba with aponeurosis of internal oblique, pubic crest and pecten pubis via conjoint tendon Thoracoabdo minal nerves (ant. rami of T6-T12) and first lumbar nerves Compresses and supports abdominal viscera Anterior Femoral Muscles Iliopsoas- Iliacus Iliac fossa, iliac crest, sacral ala Femur just distal to lesser trochanter Lumbar plexus ([L1], L2-3-4) Flexes hip and stabilizes hip joint Iliopsoas- Psoas Major Anterior transverse processes, vertebral bodies and discs (T12- L5) Lesser trochanter Ventral rami L1-4 (from lumbar plexus) Flexes hip and stabilizes hip joint
  • 5. 4 Rectus Femoris Anterior inferior iliac spine & groove superior to the acetabulum The base of the patella Femoral nerve (L2-3-4) Flexes hip and extends knee Sartorius Anterior superior iliac spine Medial aspect of the proximal tibia Femoral nerve (L2-3 [4]) Flexes, abducts and laterally rotates hip, and flexes and assists medial rotation of the knee Tensor Fascia Latae Anterior superior iliac spine and external lip of iliac crest Iliotibial Tract Superior gluteal nerve (L4-5-S1) Abducts, flexes and medially rotates hip, and assists in maintaining knee extension Medial Femoral Muscles Adductor Brevis Inferior pubic ramus Distal 2/3 pectineal line & medial lip linea aspera Obturator nerve (L2-3- 4) Adducts and flexes hip Adductor Longus Pubic crest Medial lip linea aspera Obturator nerve (L2-3- 4) Adducts and flexes hip Adductor Magnus Inferior pubic ramus, ischial ramus and tuberosity Gluteal tuberosity, linea aspera, medial supracondylar ridge and adductor tubercle of the femur Adductor region: Obturator nerve (L2-3- 4) Tibial division of the sciatic nerve (L4-5- S1) Adducts, flexes (adductor part) and extends (hamstring part) hip Gracilis Body of the pubis and Medial surface of tibia, distal Obturator nerve (L2-3- Flexes and medially
  • 6. 5 inferior pubic ramus to condyle, proximal to insertion of semitendinosus , lateral to insertion of Sartorius 4) rotates the knee and adducts hip Pectineus Superior pubic ramus Femur between the lesser trochanter and linea aspera (pectineal line) Femoral nerve and obturator nerve (L2-3- 4) Adducts and flexes hip Quadratus (Obturator) Externus Rami of pubis and ischium; external surface obturator membrane Trochanteric fossa Obturator nerve (L3-4) Laterally rotates hip Muscles of the Gluteal Region Superior Gemellus External surface of ischium via obturator internus tendon Greater trochanter Sacral plexus (L5-S1-2) Laterally rotates hip Inferior Gemellus Proximal ischial tuberosity via obturator internus tendon Greater trochanter Sacral plexus (L4-5-S1[2]) Laterally rotates hip Gluteus Maximus Aponeurosis of the erector spinae, sacrum, sacrotuberous ligament and posterior gluteal line (innominate) Greater trochanter, gluteal tuberosity of the femur and iliotibial tract Inferior gluteal nerve (L5-S1-2) Extends and laterally rotates hip Gluteus Medius External iliac surface Oblique ridge on the lateral aspect of the Superior gluteal nerve (L4-5-S1) Abducts and medially rotates hip and
  • 7. 6 greater trochanter; gluteal aponeurosis keeps the pelvis level when opposite leg is raised Gluteus Minimis External iliac surface and margin of the greater sciatic notch Anterolateral aspect of the greater trochanter Superior gluteal nerve (L4-5-S1) Abducts and medially rotates hip and keeps the pelvis level when opposite leg is raised Obturator Internus Anterolateral wall of the pelvis and obturator membrane Medial surface of the greater trochanter Nerve to the obturator internus (from the sacral plexus) (L5- S1-2) Laterally rotates hip Piriformis Anterolateral sacrum and post inf iliac spine Upper border of the greater trochanter Branch of the lumbosacral plexus ([L5]S1-2) Abducts and laterally rotates hip Quadratus Femoris Ischial tuberosity Quadrate tubercle of the femur Nerve to the quadratus femoris (from sacral plexus) (L4-5-S1[2]) Laterally rotates hip Posterior Femoral Muscles Biceps Femoris Long head: ischial tuberosity and sacrotuberous ligament Short head: lateral lip of linea aspera and lateral supracondylar line Lateral side of the fibular head Long head: Tibial branch of sciatic nerve (L5-S1- 2-3) Short head: Peroneal branch of sciatic nerve (L5-S1-2) Both heads: Flex knee Long Head: Extends hip Semimembr anosus Ischial tuberosity Posterior aspect of the Tibial division of the sciatic Extends hip and flexes and
  • 8. 7 Fig 2: Intra-articular view of the femoroacetabular joint medial tibial condyle nerve (L4-5- S1-2) medially rotates knee Semitendino sus Ischial tuberosity Proximal, medial tibia Tibial division of the sciatic nerve (L4-5- S1-2) Extends hip, and flexes and medially rotates knee Femoroacetabular Joint The femoroacetabular, or “hip”, joints are bilateral diarthrodial synovial ball-and-socket joints between the head of the femur and the acetabulum of the pelvis (Fig. 2). The hip is the second most mobile joint in the body, second only to the glenohumeral joint. The hip and the shoulder joints are often compared to due to their common classification as ball-and-socket joints, but the hip is less mobile and more stable than the shoulder. This small mobility-to-stability ratio supports the primary function of the hip joint in providing support to the weight of the trunk, head and upper limbs while in weight-bearing positions. Branches from the obturator artery, lateral circumflex femoral arteries, and superior and inferior gluteal arteries supply the hip joint with blood, while branches from the lumbar and sacral nerve plexuses provide its innervation. The following list describes the tissue layers of the femoroacetabular joints from superficial to deep, as well as the neurovasculature and other structures associated with the joints. Tissue Layers of the Femoroacetabular Region (Superficial to Deep) ● Cutaneous ○ Skin (cutis) ■ Epidermis ■ Dermis ● Subcutaneous ○ Superficial Fascia ○ Deep Fascia ○ Iliotibial band ● Muscles and tendons ○ Extension ■ Gluteus maximus ■ Biceps femoris ■ Semitendinosus ■ Semimembranosus ■ Adductor magnus
  • 9. 8 ○ Flexion ■ Sartorius ■ Tensor fascia latae ■ Rectus femoris ■ Pectineus ■ Adductor Longus ■ Iliopsoas ○ Adduction ■ Pectineus ■ Gracilis ■ Adductor brevis ■ Adductor longus ■ Adductor magnus ○ Abduction ■ Tensor fascia latae ■ Gluteus medius ■ Gluteus minimus ○ External Rotation ■ Gluteus maximus ■ Piriformis ■ Gemellus superior ■ Gemellus inferior ■ Obturator internus ■ Quadratus femoris ● Neurovascular Supply ○ Nerves ■ Lumbar Plexus □ Femoral nerve □ Obturator nerve ■ Sacral Plexus □ Nerve to the piriformis □ Nerve to the obturator internus and gemellus superior □ Nerve to the quadratus femoris and gemellus inferior □ Superior and inferior gluteal nerves □ Sciatic nerve ○ Arteries ■ Branches of: □ Obturator □ Femoral ● Medial and lateral circumflex □ Superior and inferior gluteal □ First perforating artery of profunda femoris artery ○ Veins ■ Great saphenous vein ■ Femoral vein ● Ligaments
  • 10. 9 Fig. 3: Joint Capsule of the Disarticulated Hip ○ Iliofemoral ligament ○ Pubofemoral ligament ○ Ischiofemoral ligament ○ Transverse acetabular ligament ○ Ligament of head of femur ● Joint Capsule The joint capsule of the hip is a large, strong structure attached to the acetabular rim, the intertrochanteric line, and the posterior surface of the posterior femoral neck. The capsule encloses the femoral head and most of the femoral neck, and it is relatively loose to allow for joint movements. The capsule’s internal fibers are orientated in a circular fashion, whereas the external fibers run longitudinally. The head of the femur is covered with articular hyaline cartilage, except at the fovea capitis, where the ligament of the head of the femur attaches to the femoral head. The articular cartilage of the femoral head is thickest where it bears the most weight: on its anterior and lateral surfaces and superior to its center. The acetabulum of the pelvis includes components of the iliac, ischial, and pubic bones, and it is covered by articular hyaline cartilage on its lunate surface; the half moon-shaped surface is bounded by the acetabular rim and the edge of the acetabular fossa, which is filled by a fat pad. The acetabular labrum consists of fibrocartilage lining the bowl of the acetabulum and serves to increase the stability of the joint. ● Bones ○ Femur ■ Femoral head ■ Femoral neck ■ Greater and lesser trochanters ○ Innominate ■ Ischium, ilium pubis Joint Motions The physiologic motions of the hip joint include flexion, extension, adduction, abduction, rotation, and circumduction; many of its movements are multiaxial. When the hip reaches full extension, simultaneous medial rotation occurs and acts as a “locking” mechanism to bring the femoral head into full congruence with the acetabulum. This type of movement is termed conjunct rotation. The accessory movements that occur between the joint surfaces are described in the section below on arthrokinematics. Table 2: Physiologic Motions of the Hip Joint and the Associated Muscles Joint motion Associated Muscles Flexion Iliopsoas, Rectus femoris, Sartorius,
  • 11. 10 Pectineus, Adductor longus and brevis, Tensor fascia latae, Gluteus minimus Extension Gluteus maximus, Gluteus medius (posterior fibers), Biceps femoris, Semitendinosus, Semimembranosus, Piriformis, Adductor magnus (posterior fibers) Abduction Gluteus medius, Tensor fascia latae, Gluteus minimus, Iliopsoas, Piriformis, Superior gemellus, Inferior gemellus, Obturator internus Adduction Adductor longus and brevis, Adductor magnus, Pectineus, Gracilis Medial rotation Tensor fascia latae, Gluteus medius (anterior fibers), Adductor longus and brevis, Gluteus minimus Lateral rotation Piriformis, Superior gemellus, Inferior Gemellus, Obturator internus and externus, Gluteus maximus, Sartorius, Biceps femoris (long head), Iliopsoas, Gluteus medius (posterior fibers) Planes of motion As stated previously, the hip joint functions to stabilize the head, arms and trunk during static and dynamic activities. The joint allows for three degrees of freedom, or movement in three planes, as described in Table 3. Table 3: Planes of Physiologic Motion at the Hip Plane Axis Motion Sagittal Medial-lateral Flexion and extension Frontal Anterior-posterior Abduction and adduction Transverse Longitudinal (vertical) Medial and lateral rotation The convex head of the femur articulates superiorly with the concave socket of the acetabulum and inferiorly with the fovea. The center-edge angle, a measurement commonly used in the field of orthopedic surgery, defines the fixed orientation of the acetabulum relative to the pelvis in the frontal plane. This measurement gives clinicians an indication of the percent of the femoral head that is covered by the acetabulum; it is commonly used in the diagnosis of hip dysplasia. The articular surface of the acetabulum, the lunate surface, is oriented in an anterior- inferior direction. The angle at which the femoral head articulates with the acetabulum is referred to as the angle of inclination.
  • 12. 11 Fig. 4: Angle of Inclination of the Hip Joint Angle of Inclination The angle of inclination of the hip provides information regarding the alignment of the femoral head within the acetabulum. This angle is measured in the frontal plane between the femoral neck and the femoral shaft. The magnitude of the angle decreases naturally from about 145 degrees at the time of birth to about 125 degrees in the skeletally mature adult. This decrease is due in part to the forces acting on the femur during weight bearing and partially to the increase in muscular pull on the femur as the child’s muscles develop and his or her activity level increases. An angle of inclination greater than 125 degrees is termed coxa valga (Fig. 4); it is correlated with a lengthening of the limb, an increased load on the femoral head and less-than- optimal line of pull for the hip abductors. If the angle of inclination is less than 125 degrees, the femoral neck experiences increased loading forces and the limb is shortened, but the line of pull for the abductor musculature is actually improved. This presentation is termed coxa vara (Fig. 4). Femoral Torsion Femoral torsion describes the angle formed between the longitudinal axis of the head, neck, and greater trochanter of the femur and the transverse axis of the femoral condyles when the femur is viewed along the axis of its shaft (Fig 5.). The typical angle of torsion in adults is slightly anteverted (8 - 15 degrees). Infants typically demonstrate 40 degrees of anteversion; this anteversion decreases as movement patterns and muscular lines of pull change with development. An adult with more than 15 degrees of anteversion is considered to have excessive anteversion; this configuration will result in
  • 13. 12 Fig. 5: Angle of Torsion of the Femur Fig. 6: Biomechanical Consequences of Atypical Angles of Torsion compensatory internal rotation of the hip in order to provide better congruency at the hip joint. This commonly results in an in-toeing gait pattern in these individuals. The following illustration demonstrates the relationship between femoral torsion and the functional position of the lower extremity. As shown in Figure 6, a retroverted hip occurs when the angle of torsion is less than 15 degrees (often close to zero degrees), and results in “toeing out”. When the angles of inclination and femoral torsion are within the appropriate ranges, the articulation between the femoral head and the acetabulum exhibits optimal biomechanics and may place the joint at a decreased risk for degeneration. Biomechanics and Kinematics The motion that occurs at this joint can be subdivided into femoral-on-pelvic osteokinematics and pelvic-on-femoral osteokinematics, depending on which bony structure is fixed and which is mobile. The biomechanics are described relative to the anatomical position, and each motion has a specific axis of rotation. When motion occurs in the closed kinetic chain, as during the stance phase of gait, the pelvis is moving on a fixed femur. Conversely, motion in the open kinetic chain features the femur moving on a stable pelvis, as during the swing phase of gait. The convex-concave rules of biomechanics can be applied to this ball-and-socket joint in order to better understand the motions that occur in the open and closed kinetic chains. These rules describe the arthrokinematic (joint) motions that occur in conjunction with the primary physiologic (osteokinematic) motions described in Table 3. The three chief arthrokinematic motions that can occur within a given joint are rolling, sliding, and spinning. Rolling occurs when multiple points on one articulating surface come into contact with multiple points on the other. Sliding features a solitary point on one articular surface contacting multiple points on the other. These arthrokinematic motions are illustrated in Figures 7 and 8. Spinning (not pictured here) entails a single point of one articular surface rotating on single point of the other. Arthrokinematics: Convex-on-Concave Rule When a convex surface is mobile relative to a fixed concave surface, the two surfaces roll and slide in opposite directions.
  • 14. 13 Fig. 7: Convex on Concave Arthrokinematics Fig. 8: Concave on Convex Arthrokinematics For example, when the convex head of the femur articulates with the fixed concave surface of the acetabulum during open chain hip flexion, the femoral head rolls superiorly and slides inferiorly. This motion occurs during activities such as walking, kicking or stepping over an object. Arthrokinematics: Concave-on-Convex Rule A concave surface moving on a fixed convex surface results in the rolling and sliding of two surfaces in the same direction. As the mobile, concave surface of the acetabulum moves while the convex surface of the femoral head is fixed, the two entities roll and glide in the same direction. Bending over while standing and leaning backwards while sitting in a chair are examples of this type of motion. Femoral–on-Pelvic Kinematics Hip flexion occurs in the sagittal plane with an average range of motion of 120 degrees. Hip flexion is limited at end range primarily by approximation of the soft tissues of the thigh and abdomen; less motion available if the knee is extended due to the stretch placed on the two-joint hamstring muscle group. During hip flexion, the round head of the femur moves in an inferoposterior direction within the acetabulum, thereby stretching the joint’s inferior capsule and posterior musculature. During hip extension, the femoral head moves anteriorly, increasing
  • 15. 14 Fig. 9: Sagittal Plane Motion at the Femoroacetabular Joint Fig. 10: Frontal Plane Motion at the Femoroacetabular Joint the tension on the anterior ligaments and hip flexor muscles. Typical hip extension range of motion is limited to 20 degrees, with even less motion available when the knee is flexed, due to the passive tension placed on the two-joint rectus femoris muscle. During abduction and adduction in the frontal plane, the femoral head and the distal portion of the femur move in opposite directions. As the thigh abducts, the femoral head rolls and slides inferomedially within the acetabulum; this arthrokinematic motion permits about 40 degrees of osteokinematic abduction. Abduction range of motion is primarily restricted by the pubofemoral ligament and the maximal stretch placed on the adductor musculature. Conversely, as the hip adducts, the head of the femur rolls and slides superolaterally, allowing the distal end of the femur to swing medially. Hip adduction range of motion is limited to 25 degrees and is limited as a result of stretched hip abductor musculature, the iliotibial band and the ischiofemoral ligament.
  • 16. 15 Fig. 11: Horizontal Plane Motion at the Femoroacetabular Joint Rotation of the femur on the acetabulum occurs in the horizontal (transverse) plane. It is expected that the hip’s range of motion into external rotation will exceed that of internal rotation. When the hip is fully internally rotated, the ischiofemoral ligament and the external rotator muscles are maximally stretched, thereby limiting internal rotation to about 35 degrees of motion. As the femur rotates externally, the stretch placed on the internal rotation musculature and the iliofemoral ligament allows for about 45 degrees of external rotation. Pelvi c-on-femoral osteokinematics The attachment of the axial skeleton to the pelvis creates a relationship between the pelvis, as it moves over the femoral heads, and the lumbar spine known as lumbopelvic rhythm. Ipsidirectional lumbopelvic rhythm occurs as the lumbar spine and pelvis move in the same direction, as when a person is bending forward to pick up an object from the floor. The associated displacement of the trunk helps to maximize functional movement. During contradirectional lumbopelvic rhythm, the pelvis will move one direction as the lumbar spine moves in the opposite direction. This relationship ensures that the head and trunk remain relatively stable while the pelvis rotates during ambulation. When the concave articular surfaces of the acetabulum move over the convex femoral heads, the resulting sagittal plane motions are described as anterior and posterior pelvic tilts. In the seated position (with 90 degrees of hip flexion), the iliac crests shift anteriorly to allow approximately 30 degrees of pelvic-on-femoral hip flexion; this shift establishes an anterior pelvic tilt. This anterior tilt forces the lumbar spine into a greater degree of lordosis. Along with restriction by the ligamentous scaffolding of the pelvic girdle, this increased lumbar lordosis ultimately limits further anterior displacement of the pelvis. In the standing position, anterior tilt is restricted by the hamstring muscles; the degree of restriction varies with an individual’s hamstring flexibility. Although osteokinematic hip extension is limited to 20 degrees, additional functional hip extension can be achieved by combining a posterior pelvic tilt with flexion of the lumbar spine. The posterior tilt of the pelvis increases the length in the iliofemoral ligament and rectus femoris muscle which provides “slack”, thereby reducing the resistance into extension. Range of motion into extension is limited by the iliofemoral ligament and passive tension from the rectus femoris muscles.
  • 17. 16 Fig. 13: Posterior Pelvic TiltFig. 12: Anterior Pelvic Tilt In the frontal plane, pelvic-on-femoral osteokinematics occur via a lateral tilting of the pelvis on the fixed femur. Single leg stance activities provide a clear demonstration of these motions: when the iliac crest of the non-stance limb moves superiorly, the lateral tilt is described as a “hip hike”, whereas an inferior translation of the iliac crest is termed “hip drop”. During the single leg stance phase of the typical gait pattern, pelvic-on-femoral abduction occurs as the iliac crest of the non-stance limb moves superiorly (a hip hiking motion), resulting in relative abduction of the stance leg. The lumbar spine must laterally flex towards the hiked hip to accommodate this motion and maintain the body’s center of mass within the its limits of stability (Fig. 14). An individual’s range of motion into lumbar lateral flexion is a limiting factor for his or her range into relative abduction. Other factors, including adductor muscle contracture/tightness and the passive restraint provided by the pubofemoral ligament, restrict pelvic-on-femoral abduction range of motion to 30 degrees or less. As the iliac crest of the non-stance leg moves inferiorly (a hip dropping motion), the stance leg shifts into relative adduction; the lumbar spine now laterally flexes away from the dropped hip (Fig. 14). The individual’s range of motion into lumbar lateral flexion again constrains the available range into relative adduction. Limited extensibility of the iliotibial band and hip abductor musculature can also restrict this motion. Pathologic motion can also result in what is known as compensated and uncompensated Trendelenburg Gait, which can be observed during the stance phase of the gait cycle. Compensated Trendelenburg occurs when the subject leans ipsilaterally to the side of the stance leg. If the person’s contralateral pelvis drops (when viewed in the frontal plane), this is described as an uncompensated Trendelenburg gait. During the stance phase of the gait cycle, the gluteus medius muscle, along with the other hip abductors, is responsible for keeping the pelvis in a neutral position as the body weight is loaded onto the stance leg. When this muscle group is weak or its innervation is disrupted, its function can be compromised to the point where these obvious changes in the gait cycle occur.
  • 18. 17 Fig. 14: Frontal Plane Osteokinematics of the Pelvis on the Stable Femur Fig. 15: Horizontal Plane Osteokinematics of the Pelvis on the Stable Femur Rotational motion of the pelvis on the femur in the horizontal plane can also be described in reference to single leg stance activities. As the iliac crest of the non-stance limb moves anteriorly in the horizontal plane, the stance limb hip moves into relative internal rotation. Conversely, posterior translation of the iliac crest of the non-stance limb results in relative external rotation of the stance limb hip (Fig. 15). The lumbar spine moves in synergy with the rotating pelvis by rotating itself in the contralateral direction. Table 4: Ligaments of the Femoroacetabular Joint Ligament Proximal attachment Distal attachment Function Ligamentum teres Acetabular notch Fovea of femur Conduit for neurovasculature of the femoral head Iliofemoral (Y ligament) Anterior inferior iliac spine Intertrochanteric line of the femur Controls external rotation in flexion, internal and external
  • 19. 18 Fig. 16: Comparison of the Healthy and Osteoarthritic Hip Joint rotation in extension, limits anterior translation of femoral head Pubofemoral Anterior pubic ramus Intertrochanteric fossa Controls external rotation in extension Ischiofemoral Posterior surface of the acetabular rim and labrum Capsular fibers, medial surface of greater trochanter Controls internal rotation in hip flexion and extension Common Pathologies of the Femoroacetabular Joint Hip Osteoarthritis (OA) is becoming an increasingly common pathology in the United States as the average age of the population continues to increase. OA of the hip involves degeneration of the femoral and acetabular articular cartilages, ultimately leading to a narrowing of the joint space over time. Approximately 50% of the cases of hip OA are of unknown etiology and cannot be linked to any one cause, although a history of injury to the hip joint, obesity, and the natural aging process are common predisposing factors. Typical symptoms, especially in individuals over the age of 50, include stiffness that is worse in the morning but is relieved with movement; anterior groin pain; decreased range of motion into extension, internal rotation and end range flexion; antalgic gait; and pain with activities of daily living. Altman’s Criteria for Hip OA are used as a diagnostic tool to help practitioners identify the nature of a patient’s condition without imaging (Table 5). Altman’s Criteria for hip OA has a specificity of 75% and a positive likelihood ratio of 3.4. Thus, if a patient meets all three criteria in either cluster, hip OA is the likely diagnosis. Surgical and non-surgical courses of treatment are available for treatment of hip OA. Table 5: Altman’s Criteria for Hip OA
  • 20. 19 Fig. 18: Radiograph depicting a Left Displaced Femoral Neck Fracture Fig. 17: Possible Presentations of Femoral Acetabular Impingement Cluster 1 Cluster 2 Hip pain AND Painful hip IR > 15 degrees AND Hip IR <15 degrees AND Age> 50 years old AND Flexion < 115 degrees Stiffness in the morning < 60 min duration Femoral acetabular impingement (FAI) can occur as the result of repetitive microtrauma to the labrum, articular cartilage and bone, secondary to an abnormal acetabular structure or femoral articulation. Three different types of FAI exist: pincer type, cam type, and a mixed type featuring elements of both of the former (Fig. 17). Pincer type FAI typically occurs in middle-aged females and is the result of excessive coverage of the femoral head by the acetabulum. As the femoral head makes repeated contact with the overgrown edges of the acetabulum during hip movement, the posteroinferior articular cartilage of the femoral head is progressively damaged. Cam type FAI is more common in younger males and is the consequence of an abnormal concavity along one side of the femoral head. During femoroacetabular motion, the extra bone growth on the femoral head is repetitively compressed against the lip of the acetabulum, thus producing a shearing force on the labrum over time. Symptoms of FAI include sharp groin pain during hip flexion and internal rotation; posterolateral pain with external rotation; pain when climbing stairs and/or when sitting down; and difficulty with squatting or cutting motions. Femoral fractures are a growing problem in the geriatric population: they commonly occur secondary to a fall, although in patients with extremely osteoporotic bones, the femur may actually fracture before the falling body even contacts the ground. Upon evaluation, it can be
  • 21. 20 Fig. 19: The Sacroiliac Joints within the Pelvic Girdle difficult to discern if the fracture was a direct result of a fall, or if the hip fractured first and caused the person to fall. This ambiguity is further complicated by the patient’s typically poor recall of events following the sudden shock of a fall. A proximal femoral fracture can be sustained along the femoral neck or within the intertrochanteric or subtrochanteric areas. The mechanism of injury is typically compression trauma that is sustained as a result of a direct lateral force to the hip, which can lead to subsequent soft tissue damage and possible hemorrhaging. A femoral neck fracture presents a more complex medical problem, as this type of injury usually compromises the vasculature encircling the neck. When the blood supply to the femoral head is so greatly compromised that it leads to death of the articular cartilage and subchondral bone, the result condition is termed avascular necrosis (AVN); the mortality rate associated with AVN is high, particularly in the elderly population. Sacroiliac Joints The sacroiliac (SI) joints mark the transition point between the axial and appendicular skeletons. These bilateral joints are formed by the joining of the auricular surface of the lateral sacrum and the auricular surfaces of the ilia, at vertebral levels S1-S3. They are planar synovial joints and are very stable due to their strong supporting ligaments. Each SI joint is surrounded by a joint capsule and lined with a synovial membrane. The articular surfaces of the ilia are covered in hyaline cartilage, and the articular surfaces of the sacrum are covered by fibrocartilage; the interaction between these different tissues throughout the aging process can lead to fibrous adhesions across the joint cavity. A number of other changes occur within the aging SI joint. For example, the articular surfaces of the joints are smooth in the newborn, but become more irregular with age due to the loading forces imposed by a variety of weight bearing activities. The SI joint is initially diarthrodial and moves easily, but between puberty and young adulthood, it changes into a modified amphiarthrodial joint, permitting only slight motion. Osteophytes in and around the joint are common, even in the young adult. By the 8th decade, the hyaline cartilage has deteriorated; in some cases, the joint ossifies completely. Degenerative changes may develop secondary to certain pathologies, but they are more often the joint’s natural response to years of weight bearing and force transference. The movement available at the SI joint is limited due to its strong stabilizing ligaments and intrinsic structure of the joint. Females generally have more mobility at this joint than males, and the joint’s range of motion increases during pregnancy and childbirth. In both sexes, however, the movement available at these joints decreases with age.
  • 22. 21 As previously discussed, the role the SI joints play in transferring forces between the trunk and the lower extremities places them under unique structural demands. The SI joints form part of the pelvic ring, which also consists of the sacrum, the innominate bones, and the pubic symphysis. The integrity of the pelvic ring depends on the stability of the sacrum, which lies between the two innominate bones and is connected to them via the SI joints; the stability of the SI joints therefore plays a critical role in maintaining the overall functionality of the pelvic girdle. In addition to serving as a means for load transfer, the SI joint acts a “shock absorber” to attenuate some of the forces the pelvis experiences during loading. Tissue Layers of the Sacroiliac Region (Superficial to Deep) ● Cutaneous ○ Skin (cutis) ■ Epidermis ■ Dermis ● Subcutaneous ○ Superficial fascia ■ Contains fat, cutaneous nerves, superficial veins, lymph vessels, lymph nodes ○ Deep fascia ● Muscular Fascia ○ Thoracolumbar fascia ● Muscles ○ Biceps femoris – long head ○ Erector spinae ○ External and internal obliques ○ Gluteus maximus ○ Iliacus ○ Latissimus dorsi ○ Lumbar multifidus ○ Piriformis ○ Rectus abdominis ○ Transversus abdominus ● Neurovascular Supply ○ Nerves ■ Dorsal rami of sacral nerves S1 – S4 ■ Anterior rami of sacral nerves S1-S2 ■ Superior gluteal nerve ○ Arteries ■ Posterior division of internal iliac arteries □ Iliolumbar arteries □ Lateral sacral arteries □ Superior gluteal arteries ○ Veins ■ Common iliac vein ● Ligaments
  • 23. 22 ○ Anterior Sacroiliac Ligament ○ Interosseous SI Ligament ○ Short and Long Dorsal SI Ligament ○ Iliolumbar Ligament ○ Sacrotuberous Ligament ○ Sacrospinous Ligament ● Joint Capsule ○ Attaches along margins of auricular surfaces of sacrum and ilium and is thickened anteriorly as the anterior sacroiliac ligament. Joint Motions The SI joints allow for a small amount of sacral rotation with respect to the innominate bones. Among experts, controversy abounds concerning the actual amount of motion available at these joints, and the extent to which this movement impacts symptomatic pathology. Synovial joints are generally perceived to be highly mobile, but despite their synovial classification, movement of the SI joint is extremely restricted by its stabilizing ligaments. Along with the pubic symphysis, these joints allow for small rotational and gapping movements, which reduce the stress transferred to the pelvis from the trunk and lower limbs. The principal motions of the SI joints are nutation and counternutation, as discussed in the following sections. Biomechanics and Kinematics The SI joints are regarded as a biomechanical “buffer” between the vertebral column, the lower extremities, and the ground reaction force. The primary functions of the SI joints are as follows: stabilization of the pelvis; transference of gravitational forces acting on the vertebral column to the lower extremities; and distribution and attenuation of ground reaction forces exerted upon the lower extremities during weight bearing. The SI joints are semicircular in shape, and the joint plane is oriented vertically (Fig. 20) near-sagittal plane. The motions of the SI joints are unique in that they are small, difficult to define, and not directly controlled by active contraction of the surrounding musculature. It has been estimated that the total amount of SI joint motion occurring in the mature adult skeleton ranges from 1-4 degrees of rotation and 1-2 mm of translation in the horizontal plane. These ranges can increase significantly during pregnancy as result of the hormonally induced increase in joint laxity required for vaginal delivery of the infant. Due to the complexity of the translational and rotational motions that occur at the SI joint, unique terminology has been adopted to describe its biomechanics. The terms nutation and counternutation describe the near-sagittal plane motions of the SI joint relative to the fixed ilium (Fig. 21). Nutation can be likened to anterior rotation: it refers to a coupling of the inferior and anterior shift of the sacral promontory with the posterior movement of the apex of the sacrum and the coccyx. Conversely, counternutation is comparable to posterior rotation: it describes a relative posterior tilt of the sacral promontory paired with a simultaneous anterior translation of the sacral apex and coccyx. It is important to note that these osteokinematic motions of the SI
  • 24. 23 Fig. 20: Transverse Section through the Sacroiliac Joints Fig. 22: Locking Mechanismof the Fully Nutated SI Joint joints can occur when the sacrum moves on the iliac bones, when the ilia rotate on the sacrum, or when both movements are occurring simultaneously. D urin g nuta tion, the ischi al bone s move apart and the iliac bones are approximated. The opposite occurs during counternutation, as shown in Figure 21. Both nutation and counternutation are limited by various ligaments of the SI joint, which are described in detail in Table 6. When the sacrum is fully nutated, the SI joint is in its close-packed position: that is, there is maximal contact between the joint surfaces and maximal tension across its ligaments. The forces generated by gravity, ligamentous tension, and muscular contraction increase the compressive and shearing forces between the articulating surfaces of the joint. When the sacrum is in full nutation, these compressive forces create optimal stability for the SI joints. During weight bearing, the force of gravity acting through the vertebral column creates a torque that rotates the sacrum anteriorly relative to the ilium. Simultaneously, the compressive force of the femurs against the acetabula acts to rotate the ilia posteriorly relative to the sacrum. This phenomenon is referred to as the nutation torque, and it ultimately results in a “locking” of the SI joint (Figure 22). The nutation torque mechanism demonstrates how motion of the SI joint is dictated primarily by the force of gravity, rather than by the actions of muscles or ligaments. The muscles involved in nutation and counternutation (Table 6) act on either the sacrum or the innominate bones. For example, the erector spinae muscles nutate the sacrum, while the Fig. 21: Physiologic Motions of the Sacroiliac Joints
  • 25. 24 Fig. 23: Ligaments of the Sacroiliac Joint pelvic floor muscles balance their action with reciprocal counternutation. The muscles that act to nutate and counter-nutate the pelvis are detailed in Table 6. Table 6: Physiologic Motions of the SI Joint and the Associated Muscles Joint Motion Associated Muscles Nutation Multifidus, erector spinae, rectus abdominis, biceps femoris, adductor magnus Counternutation Rectus femoris, Sartorius, pectineus, adductor longus, adductor brevis, latissimus dorsi Compression Internal oblique, transversus abdominis Ligaments During vigorous, high impact activities such as running or jumping, greater demands are placed on the SI joint; in these situations, the ligaments and muscles that cross the SI joint play significant roles in its stabilization. The ligaments become stretched as the nutation torque produced by gravity increases. As the tension in these ligaments increases (Fig. 23 and Table 7), the compression forces acting on the SI joint also increase. This direct relationship between ligamentous tension and joint compression force ensures optimal stability of the joint during dynamic tasks. Table 7: Ligaments of the SI Joint Ligament Proximal Attachment(s) Distal Attachment(s) Functions Anterior sacroiliac* Anterior surface of the lateral part of the sacrum Margin of the auricular surface of the Ilium Reinforce anterior and inferior aspects of joint capsule
  • 26. 25 Iliolumbar* Lower part of the transverse processes of the 4th and 5th lumbar vertebrae Anterior part of the upper surface of the sacrum, crest of the ilium Reinforce anterior and inferior aspects of joint capsule Interosseous* Auricular surface of the sacrum Iliac tuberosity Transfer weight of upper body from axial skeleton to the ilia; Resists anterior and inferior movement of the sacrum Short and long posterior sacroiliac* Short: posterior- lateral side of sacrum Long: from regions of 3rd and 4th sacral segments Short: Ilium near iliac tuberosity Long: posterior- superior iliac spine Reinforce the posterior aspect of the joint; Resists counternutation of the sacrum on the ilium during weight bearing Sacrotuberou s Posterior-superior iliac spine, lateral sacrum, and coccyx Ischial tuberosity Indirect (secondary) stabilization of the joint, prevents upward tilting of lower end of sacrum; Resists nutation of the sacrum on the ilium during weight bearing Sacrospinous Lateral margin of caudal end of the sacrum and coccyx Ischial spine Indirect (secondary) stabilization of the joint, prevents upward tilting of lower end of sacrum; Resists nutation of the sacrum on the ilium during weight bearing *indicates primary stabilizing ligaments The thoracolumbar fascia also plays a key role in the stabilization of the SI joint. The posterior layer of the thoracolumbar fascia lies superficial to the erector spinae and the latissimus dorsi, and it attaches to the
  • 27. 26 Fig. 24: Transverse Section Depicting the Layers of the Thoracolumbar Fascia Fig. 25: Fortin’s Area Fig. 26: Radiograph of a Right SI Joint Dislocation spinous processes of the five lumbar vertebrae, the sacrum, and the ilia (Fig. 24). Due to its direct attachment to both the sacrum and the ilia, this layer of the thoracolumbar fascia provides critical mechanical stability to the SI joint. Common Joint Pathology SI joint pain has been reported in 15-30% of patients who present with low back pain. Although the pattern of pain referral from the SI joint tends to be variable, a common location of referred pain is the region immediately inferior to the posterior inferior iliac spine; a presentation of loc aliz ed pain 1 cm posterior to the PSIS is referred to as Fortin’s sign (Fig. 25). Although it is poorly understood, the primary mechanism of injury to the SI joint is thought to be the result of axial loading in combination with rotation. SI pain can also be the consequence of a vast array of pathological changes, including capsular and ligamentous tension, hypo- or hypermobility, abnormal joint mechanics, soft tissue injury, and inflammation. Common intra- articular pain generators include osteoarthritis and infection, whereas fractures, ligamentous injury, and myofascial pain are categorized as extra-articular sources of pain. Risk factors for the development of SI joint pain include leg length discrepancy, gait or postural abnormalities, prolonged vigorous exercise, scoliosis, spinal fusion to the sacrum, pregnancy, and repetitive and unidirectional high velocity motions, (i.e. kicking, swinging, throwing). Direct injury and dislocations of the SI joint can occur secondary to sudden traumatic or shearing forces, as occur when a person unexpectedly steps down from a high curb or into a hole, or falls directly onto the SI joint (Fig. 26). Pubic Symphysis The pubic symphysis is a cartilaginous joint located at the inferior aspect of the abdomen, just superior to the external genitalia; it forms the interface between the two pubic bones. The medial symphyseal surfaces of the pubic bones are separated by a fibrocartilaginous disc. These joint surfaces are covered with hyaline articular cartilage that blends with the disc. The joint is minimally mobile and is thus classified as a synarthrosis. The main function of the pubic symphysis is the absorption and attenuation of forces throughout the anterior pelvic ring,
  • 28. 27 especially during weight bearing activities and the acute stresses induced by pregnancy and childbirth. The following list describes the tissue layers of the pubic symphysis, superficial to deep, as well as the neurovasculature and other structures associated with the joint. Tissue Layers of the Pubic Symphyseal Region (Superficial to Deep) ● Cutaneous ○ Skin (cutis) ■ Epidermis ■ Dermis ● Subcutaneous Tissue ● Superficial Fascia ○ Camper’s Fascia ■ Mons pubis ○ Scarpa’s Fascia ● Muscles ○ Rectus abdominus ○ Abdominal external oblique ○ Abdominal internal oblique ○ Transversus abdominis ○ Gracilis ○ Pectineus ○ Adductor longus ○ Adductor brevis ○ Adductor magnus ● Neurovascular Supply ○ Nerves ■ Branches of: □ Iliohypogastric □ Ilioinguinal □ Pudendal □ Genitofemoral ○ Arteries ■ Branches of: □ Obturator □ Inferior epigastric □ Pudendal ○ Veins ■ Internal iliac vein ● Ligaments ○ Anterior pubic ligament ○ Posterior pubic ligament ○ Inferior pubic (arcuate) ligament ○ Superior pubic ligament ● Joint Capsule
  • 29. 28 Fig. 27: Ligaments of the Pubic Symphysis, Schematic Biomechanics and Kinematics As a cartilaginous synarthrosis, the adult pubic symphysis permits a very small amount of rotation and translation under normal physiologic conditions. The joint’s wedge-shaped fibrocartilaginous disc is wider superiorly and inferiorly and more narrow in the middle with its apex is directed posteriorly. The disc functions to resist tensile, shearing and compressive forces within the joint. The width of the joint space ranges from 3 – 10 mm and varies with age and gender. The articular surfaces are convex, ovular in shape, and are oriented obliquely within the sagittal plane. During functional activities like standing, sitting and single leg stance, the pubic symphysis experiences compressive, traction, and shearing forces. Due to the small magnitude of movement permitted at this joint, research regarding the biomechanics of this joint is scarce. A 2010 study by Becker, et al. reported that less than one degree of rotation occurs about the sagittal axis in the coronal plane and about the horizontal axis in the sagittal plane. Table 8: Ligaments of the Pubic Symphysis Ligament Attachment(s) Functions Superior pubic ligament Superior aspects of pubic bodies, interpubic disc, pubic tubercles Joint stability and reinforcement Inferior pubic (subpubic or arcuate) ligament Inferior pubic rami, interpubic disc, posterior pubic ligaments Forms the apex of the pubic arch Anterior public ligament Periosteum laterally, interpubic disc Joint stability and reinforcement Posterior pubic ligament Periosteum of pubic bodies posteriorly Joint stability and reinforcement
  • 30. 29 Fig. 28: Ligaments of the Pubic Symphysis, In Situ Fig. 29: Radiograph of a Pelvis with Dysfunction of the Pubic Symphysis Fig. 30: Non-grid Pelvic Support Belt Used to Support the Pelvis of Pregnant Women with Symphysis Pubis Dysfunction Common joint pathology Symphysis pubis dysfunction, which commonly occurs during pregnancy, is defined as mild to severe pain in the pubic region, the groin, and the medial aspect of the thigh. This pain often co-occurs with sacroiliac, low back and suprapubic pain, and it can profoundly affect the woman’s quality of life. Patients with this dysfunction may demonstrate a “waddling” gait adopted in an attempt to attenuate the pain and possible clicking or grinding sensations associated with weight bearing activities. The increased release of reproductive hormones during pregnancy induces greater laxity in the supportive ligaments of the pelvis; as a result, the entire pelvic girdle becomes increasingly unstable as pregnancy progresses. A study conducted by Depledge, et al found that exercise and the use of a non-grid pelvic support belt (Fig. 30) reduced the subjects’ pain and increased their functional mobility. Osteitis pubis is a common pathology among athletes, particularly soccer and hockey players. Osteitis pubis is a non-infectious inflammatory condition of the symphysis pubis that can also occur following trauma or secondary to rheumatic disorders or pregnancy. Pain typically refers to the groin, the lower abdomen, and/or the region directly superficial to the pubic symphysis. In the athletic population, this condition can occur as the result of mechanical traction microtrauma caused by an imbalance between the abdominal muscles and the hip adductors. The patient will often complain of pain during resisted hip adduction and active contraction of the abdominal
  • 31. 30 Fig. 31: Bone Scan (left) and CT Scan (right) of a Pelvis with Osteitis Pubis muscles. Bone scans will reveal elevated isotope uptake at the pubic symphysis (Fig. 31, left) CT scans will demonstrate erosion of one or both of the articular surfaces (Fig. 31, right). Osteitis pubis condition often co-occurs with osteomyelitis pubis, an infection of the pubic bone itself that presents similarly to osteitis pubis. A failure of conservative treatment for osteitis pubis typically implicates osteomyelitis pubis as the causative pathology. Osteomyelitis pubis, unlike osteitis pubis, is not self limiting and requires identification of the offending organism and treatment with the correct antibiotics. Knee Complex Introduction to the Knee The knee is the largest joint in the body. It consists of the tibiofemoral and patellofemoral joints contained within a single joint capsule. The proximal tibiofibular joint located on the lateral surface of the knee is also falls within this region, though it is not contained within the capsule. Motion at the knee occurs in two planes. Its primary actions are flexion and extension in the sagittal plane. The secondary actions of the knee complex are internal and external rotation in the transverse plane, physiological motions which typically occur in conjunction with movement at other joints in the lower extremity. Interactions between the hip, knee, and ankle allow for performance of many daily functional activities such as walking, running, standing, and sitting. The function of the knee is inextricably linked to that of the rest of the lower extremity due to the fact that approximately two thirds of the muscles crossing the knee also cross either the hip or the ankle. During the initial swing phase of gait, for example, knee flexion occurs passively in response to the active hip flexion and ankle dorsiflexion required to lift and clear the foot. In addition, muscles acting on the knee function in a primarily eccentric fashion. The knee extensors contract eccentrically during the loading response of gait in order to absorb the shock of heel contact and weight acceptance. The knee flexors eccentrically control passive extension of knee during terminal swing. The stability of the knee derives from the surrounding soft tissue like muscles and ligaments, rather than from its bony configuration. Without these soft-tissue restraints, the large
  • 32. 31 femoral condyles would not maintain sufficient contact with the nearly flat articular surfaces of the proximal tibia. However, during closed kinetic chain (CKC) activities when the foot is firmly planted, these vital restraints are at an increased risk for damage. Injury to these tissues reduces the stability of the joint and is the etiology of most common pathologies of the knee. Table 9: Muscles of the Knee Region Muscle Action Proximal Attachment Distal Attachment Segmental Innerva- tion Peripheral Innerva- tion Rectus femoris Extends knee; flexes hip Anterior inferior iliac spine & groove superior to the acetabulum The base of the patella L2, 3, 4 Femoral nerve Vastus intermedius Extends knee Anterior aspect of the proximal 2/3rds of the femoral shaft Lateral border of the patella L2, 3, 4 Femoral nerve Vastus lateralis Extends knee Intertrochanteri c line, greater trochanter, gluteal tuberosity and linea aspera Base and lateral border of the patella L2, 3, 4 Femoral nerve Vastus medialis Extends knee Intertrochanteri c line, spiral line, linea aspera and medial supracondylar line Base and medial border of the patella L2, 3, 4 Femoral nerve
  • 33. 32 Sartorius Flexes and assists medial rotation of the knee; flexes, abducts, and laterally rotates hip, and Anterior superior iliac spine Medial aspect of the proximal tibia (apart of the pes anserine) L2, 3, [4] Femoral nerve Tensor fasciae lata Assists in maintaining knee extension (via iliotibial band); abducts, flexes and medially rotates hip Anterior superior iliac spine and external lip of iliac crest Iliotibial band L4, L5, S1 Superior gluteal nerve Articularis Genu Pulls articular capsule proximally Distal anterior shaft of femur Proximal portion of synovial membrane of knee joint L2, 3, 4 Femoral Gracilis Flexes and medially rotates the knee; adducts hip Body of the pubis and inferior pubic ramus Medial surface of tibia, distal to condyle, proximal to insertion of semitendinosus , lateral to insertion of Sartorius (apart of the pes anserine) L2, 3, 4 Obturator
  • 34. 33 Gluteus Maximus Assists to stabilize the knee in extension (via iliotibial band) Aponeurosis of the erector spinae, sacrum, sacrotuberous ligament and posterior gluteal line of innominate Greater trochanter, gluteal tuberosity of the femur and iliotibial tract L5, S1, S2 Inferior gluteal nerve Semimem- branosus Flexes and medially rotates knee; extends hip Ischial tuberosity Posterior aspect of the medial tibial condyle L4, L5, S1, S2 Sciatic nerve (tibial division) Semitend- inosus Flexes and medially rotates knee; extends hip Ischial tuberosity Proximal, medial tibia L4, L5, S1, S2 Sciatic nerve (tibial division) Biceps Femoris: short head Flexes and laterally rotates knee Lateral lip of linea aspera and lateral supracondylar line Lateral side of the fibular head L5, S1, S2 Sciatic nerve (fibular division) Biceps Femoris: long head Flexes and laterally rotates knee; extends hip Ischial tuberosity and sacrotuberous ligament Lateral side of the fibular head L5, S1, S2, S3 Sciatic nerve (tibial division) Popliteus Flexes and medially rotates knee Lateral femoral condyle and oblique popliteal ligament Soleal line of the tibia L4, L5, S1 Tibial Gastroc- nemius Flexes knee; plantar Posterior aspect of the femoral condyles and Posterior calcaneal surface S1, S2 Tibial
  • 35. 34 flexes ankle joint capsule Plantaris Flexes knee; plantar flexes ankle Lateral supracondylar line Posterior calcaneal surface L4, L5, S1, S2 Tibial Neurovascular Supply to the Knee The popliteal artery is the main source of blood supply to the knee. It is a continuation of the femoral artery, which becomes the popliteal artery after passing through the adductor hiatus, an opening in the adductor magnus muscle just superior to the femoral epicondyles. The popliteal artery then dives deep within the popliteal fossa, coursing along the surface of the joint capsule until it reaches the inferior border of the popliteus muscle. At this point, the popliteal artery bifurcates into posterior and anterior tibial arteries. Immediately superior to this bifurcation, the popliteal artery gives off five genicular branches which anastomose around the tibiofemoral and patellofemoral joints. These branches include the following: ● Superior lateral and superior medial genicular arteries, which encircle the femoral condyles and the superior patella ● Middle genicular artery, which supplies the anterior and posterior cruciate ligaments ● Inferior lateral and inferior medial genicular arteries, which encircle the tibial condyles and inferior patella. This bundle of arteries is referred to as the genicular anastomosis (Fig. 32). The descending branch of the lateral circumflex femoral artery and the descending genicular artery both run anterior to the knee. Just superior to the patella, they join an anastomosis with the superior genicular arteries (medial and lateral). Just inferior to the patella, the inferior lateral and inferior medial genicular arteries anastomosis with the superior lateral and superior medial genicular arteries, respectfully. The final two branches of the genicular anastomosis are the Figure 32: Genicular Anastomosis anterior and posterior tibial recurrent arteries, which ascend from the anterior tibial artery to contribute the vascular supply of the knee. The anastomotic arrangement of these arteries is crucial to ensuring that the knee joint maintains continuous blood supply regardless of its position. When the knee is fully flexed, for example, the popliteal artery can become compressed
  • 36. 35 Figure 33: Cutaneous Nerve Distribution of the Lower Extremity within the popliteal fossa, leading to an interruption of its blood flow. However, the anastomoses around the knee ensure that oxygenated blood continues to supply the joint despite the temporary obstruction of the popliteal artery. The sciatic nerve provides the innervation of the knee joint and surrounding tissues. Immediately superior to the popliteal fossa, the sciatic nerve bifurcates into the tibial nerve and the common fibular nerve; these peripheral nerves contain fibers from the anterior and posterior divisions of the sacral plexus, respectively. Just proximal to this bifurcation, the sciatic nerve gives off multiple muscular branches which supply the hamstrings. The tibial nerve is the larger component of the bifurcated sciatic nerve. It descends inferiorly through the popliteal fossa, running with the popliteal vessels. The tibial nerve gives off branches to innervate the muscles that attach proximally to the posterior knee. Immediately superior to the two heads of the gastrocnemius muscle, the tibial nerve gives rise to the medial sural cutaneous nerve, which courses superficially over the lateral head of the gastrocnemius to supply the skin of the posterolateral leg. The common fibular nerve courses parallel to the distal portion of the biceps femoris muscle. Echoing the branching of the tibial nerve, the common fibular nerve gives off the lateral sural cutaneous nerve immediately superior to the proximal attachments of the gastrocnemius muscle. This nerve descends along the posterolateral aspect of the gastrocnemius to supply the skin of the posterolateral surface of the proximal leg. The common fibular nerve continues inferiorly down the leg, traveling along the posterolateral aspect to curve around the fibular head, where it then bifurcates into superficial and deep fibular branches. Both of these nerves descend along the lateral aspect of the tibia , with the deep fibular nerve staying closer to the tibia and the superficial nerve approximating closer to the skin. Both branches ultimately ramify in dorsum of the foot. At the approximate midpoint of the posterior leg, the medial and lateral sural cutaneous nerves join to form the sural nerve. The sural nerve innervates the skin on the posterolateral aspect of the leg and foot. The femoral nerve and its branches are the main source of innervation to the anterior lower limb. While the femoral nerve gives off branches to the muscles of the anterior thigh (e.g., the quadriceps and the sartorius) and provides cutaneous sensation to the anteromedial thigh, most of its motor fibers have actually terminated by the time it reaches the knee. Therefore, most of the anterior knee nerve supply is cutaneous providing sensory innervation.
  • 37. 36 The anterior femoral cutaneous branches supply the skin of the anteromedial thigh and knee; similarly, the lateral femoral cutaneous branches supply the skin of the anterolateral thigh and knee. While most of the cutaneous branches from the femoral nerve are restricted to the anterior surface of the lower extremity, the femoral nerve provides a few posterior femoral cutaneous branches, which supply the skin over the popliteal fossa. The saphenous nerve is the terminal branch of the femoral nerve; it provides cutaneous sensation to the skin of the inferior anteromedial knee. The cutaneous nerve distribution and the dermatomes of the lower extremity vary, but they generally comprise L2 – L5 anteriorly and S1 and S2 posteriorly (Fig. 33). Tissue Layers of the Knee Region (Superficial to Deep) ● Epidermis ● Dermis ● Adipose ● Fascia ○ Tensor fascia lata ■ Iliotibial band ■ Intermuscular septa ○ Medial and lateral patellar retinaculum ● Muscle and Tendons ○ Sartorius ○ Rectus femoris ○ Vastus lateralis ○ Vastus medialis ○ Patellar tendon ○ Gracilis ○ Biceps femoris ○ Semimembranosus ○ Semitendinosus ○ Gastrocnemius ○ Plantaris ○ Popliteus ● Bursa ○ Prepatellar ○ Infrapatellar ○ Deep infrapatellar ○ Suprapatellar ○ Subpopliteal ○ Pes anserine ● Neurovasculature ○ Common fibular nerve ■ Lateral sural cutaneous nerve
  • 38. 37 ○ Tibial nerve ■ Medial sural cutaneous nerve ○ Sural nerve ○ Popliteal artery ■ Superior medial genicular a. ■ Superior lateral genicular a. ■ Middle genicular a. ■ Inferior medial genicular a. ■ Inferior lateral genicular a. ● Extracapsular and capsular ligaments ○ Lateral collateral ligament (LCL) ○ Anterolateral ligament (ALL) ○ Medial collateral ligament (MCL) ■ Superficial and deep ● Joint capsule ○ Fibrous capsule ○ Synovial membrane ○ Articular cartilage ■ Femoral condyles ■ Tibial plateau ○ Menisci ■ Medial ■ Lateral ○ Intracapsular ligaments ■ Anterior cruciate ligament (ACL) ■ Posterior cruciate ligament (PCL) ○ Synovial fluid The Tibiofemoral Joint The tibiofemoral joint is formed by the articulation between the convex femoral condyles (medial and lateral) and the primarily flat surfaces of the tibial condyles. The large femoral condyles provide significant surface area for articulation with the tibia; this permits a large range of motion in the sagittal plane and is important for performance of dynamic, lower extremity- driven activities like running, biking, and climbing. The consequence of a large range of motion, however, is a reduction in overall joint stability: the intra-articular space of the tibiofemoral joint is rather wide and loose, so stability is provided by the menisci, the knee ligaments and joint capsule, the surrounding musculature, and the compressive force of gravity (i.e., body weight). Table 10: Physiologic Motions of the Tibiofemoral Joint and the Associated Muscles
  • 39. 38 Motion Primary Associated Muscles Secondary Associated Muscles Knee Flexion Hamstrings (long head and short head of the biceps femoris, semimembranosus, semitendinosus) Gastrocnemius, gracilis, plantaris, sartorius, popliteus Knee Extension Quadriceps (rectus femoris, vastus lateralis, vastus medialis, vastus intermedius) Tensor fascia lata Knee Internal Rotation Semimembranosus, semitendinosus Gracilis, sartorius Knee External Rotation Biceps femoris N/A Biomechanics and Kinematics of the Tibiofemoral Joint The bony structure of the tibiofemoral joint is distinct in both its anterior and posterior aspects. Anteriorly, the medial and lateral femoral condyles are covered by articular cartilage. Between the condyles lies the shallow intercondylar groove, which articulates with the posterior surface of the patella (discussed in detail below: see “The Patellofemoral Joint”). Posteriorly, there is still articular cartilage, but there is a deep intercondylar fossa that lies between the medial and lateral femoral condyles; the cruciate ligaments intersect within this fossa. Due to the angle of inclination of the femur (125 degrees in a typical adult), the femoral shaft deviates medially towards midline. In order to establish a vertical orientation of the tibia, the tibiofemoral joint exhibits a lateral angle of approximately 170 to 175 degrees (Fig. 34). This normal alignment creates a slight genu valgus, or “knock-knee”, positioning at the joint. Variations in the degree of this lateral angle are common and can lead to excessive genu valgum (a lateral angle less than 165 degrees) or genu varum, or “bow-leg”, (a lateral angle greater than 180 degrees), as depicted in Figure 34B. A measurement technique known as the Q (for “quadriceps”) angle can quantify these positions and objectively describe the alignment of the knee in the context of the entire lower extremity.
  • 40. 39 Figure 34: Angle of Inclination of the Femur The Q angle is formed at the intersection of a line visually drawn from the anterior superior iliac spine (ASIS) to the midline of the patella, and a line from the patellar midline to the tibial tuberosity. The tibiofemoral joint is classified as a synovial, bicondylar joint with two degrees of freedom. Its primary motions are flexion and extension in the sagittal plane. When the knee is slightly flexed, slight axial (internal and external) rotation may occur in the transverse plane. The femoral condyles are not perfectly rounded; these asymmetrical articular surfaces cause the medial-lateral rotatory axis to vary as the knee flexes through its available range. The range of motion available in these two planes can vary, especially with age and gender. However, typical motion in the sagittal plane ranges from 130 – 150 degrees of flexion to 0 – -5 degrees of extension (this implies that an individual presenting with 5 degrees of hyperextension falls within the range of normal). Range of motion in the transverse plane depends upon the degree of knee flexion. If the knee is flexed to 90 degrees, total axial rotation is typically 40 to 45 degrees. Range of motion into external rotation is generally double that of internal rotation. When the knee is fully extended (to 0 degrees), axial rotation is restricted. As the knee moves from flexion into extension, external rotation serves to “lock” the joint into full extension. This position of full knee extension with external rotation is the closed-packed position of the knee, indicating maximal bony congruency between the femoral condyles and the tibial plateau. This mechanism will be discussed further in the “Joint Configuration” section below. The tibiofemoral joint capsule is large and lax to allow for the extensive range of motion required during many functional and recreational activities. The capsule also contains synovial fluid, which facilitates smooth movement of the tibiofemoral joint. Despite its relative laxity, however, the capsule does provide some restraint of motion in all various directions. The capsule is composed of a superficial fibrous layer and a deep synovial membrane. The fibrous layer is continuous with the iliotibial band, the extensor retinaculum of the ankle, and some ligaments of the knee. The capsule also supplies proprioceptive input and pain signals to the central nervous system via its intrinsic mechanoreceptors and nociceptors. The muscles that cross the tibiofemoral joint provide additional support and restraint of motion: for example, the pes anserine group, composed of the sartorius, the gracilis, and the semitendinosus muscles, resists external rotation and valgus forces at the knee. Many muscles act on the knee to provide movement in the sagittal and transverse planes. A single muscle group, the quadriceps femoris, is responsible for knee extension: it includes the rectus femoris and the vastii (lateralis, medialis, and intermedius) muscles. The vastii provide approximately 80% of knee extension torque, while the rectus femoris provides the remaining 20% and is critical to achieving full knee extension. Since the rectus femoris crosses the hip joint via its proximal attachment at the anterior superior iliac spine, it also contributes to hip flexion; this actions assists movement of the limb through the swing phase of the gait cycle. The vastus lateralis has the largest cross-sectional area of the quadriceps muscles, affecting the lateral
  • 41. 40 pull of the patellofemoral joint (further discussed in the “Patellofemoral Joint” section). In addition, the oblique fibers of the vastus medialis and lateralis create a force upon the patella. In order for the patella to glide smoothly and stably within the intercondylar groove, each of these two vastii must directly counteract the pull of the other. The vastus intermedius works in synergy with the other quadriceps muscles to draw the joint capsule superiorly as the knee extends (these biomechanics are discussed further in “The Patellofemoral Joint”, below). The muscles that cross the posterior knee generate movement into flexion and axial rotation. The gastrocnemius and plantaris muscles produce pure knee flexion without a rotatory component. The biceps femoris is the only muscle that can flex and externally rotate the knee. The remaining muscles flex and internally rotate the knee to varying degrees. Although the biceps femoris must counteract the pull of several internal rotators, its moment arm for rotation is longer than those of the internal rotators: its distal attachment on the fibular head increases the distance between the muscle fibers and the the axis of rotation, particularly when the knee is flexed to 90 degrees. Consequently, the biceps femoris alone can provide the enough torque into external rotation to counterbalance the internal rotators and maintain the knee in a position of neutral rotation. The knee extensors provide approximately 66% more torque than the knee flexors. The extensors produce maximal torque when the knee is positioned in 45 – 70 degrees of flexion; significantly less torque is produced at either extreme of flexion or extension. These variations in extension torque stem from changes in muscle and moment arm lengths throughout the joint’s range of motion; patellar movement and axial rotation of the tibiofemoral joint also impact the extension torque available at any given location in the arc of motion. Maximal knee flexion torque occurs when the joint is flexed between 0 – 20 degrees. Although the moment arm for the hamstring group is greatest when the knee is flexed from 50 – 90 degrees, the length-tension relationships of these muscles play an important role in determining the position of maximal torque production. With exception of the short head of the biceps femoris, the hamstrings are all two-joint muscles; therefore, the concomitant degree of hip flexion directly affects the length- tension relationship of the hamstrings and thus their ability to produce a flexion moment at the knee. For example, hip flexion elongates the hamstrings at their proximal attachment, allowing for increased production of flexion torque at the knee; hip extension has the opposite effect. During closed kinetic chain movements (i.e., any movement in which the foot is fixed in a weight bearing position), the external demand moment at the knee is greatest when the knee is flexed to 90 degrees; external demand decreases as the knee extends. Functionally we would have to exert less quadriceps force (to extend the knee and stand up) compared to squatting down. However, during open kinetic chain, or non-weight bearing, movements, the external demand moment is greatest when the knee is extended to 0 degrees; it decreases as the knee is flexed (Fig. 35). In a functional context, this relationship means that sitting in a chair with the knees in varying degrees of flexion (Fig. 35A-B) will require less extensor (quadriceps) activity than would be required to maintain terminal knee extension in the seated position (Fig. 35C).
  • 42. 41 Figure 35: Open Chain Knee Extension Ligaments of the Tibiofemoral Joint The two intra-articular cruciate ligaments of the tibiofemoral joint intersect within the intercondylar space, forming the cross shape that gives them their name. Each is named based on the location of its attachment to the articular surface of the tibia. Thus, the anterior cruciate ligament (ACL) attaches to the anterior surface of the tibial plateau and the posterior cruciate ligament (PCL) attaches to the posterior surface of the plateau (Fig. 36). They both rely on vasculature within the synovial membrane for their blood supply. The cruciate ligaments are thick, strong structures that provide a significant amount of stability to the tibiofemoral joint by resisting shear forces in the sagittal plane. The cruciates also contain mechanoreceptors, which provide the central nervous system (CNS) with proprioceptive feedback regarding the position of the knee joint.
  • 43. 42 Figure 37: Anterior Slide of Tibia on Femur The anterior cruciate ligament functions primarily to prevent anterior shear of the tibia on the femur, as may occur when the knee approaches full extension in the open kinetic chain (Fig. 37). The knee moves into the final 50 – 60 degrees of open-chain knee extension, the contraction of the quadriceps pulls the tibia anteriorly on the femur. When the ACL becomes taut in this position, thereby limiting the extent of this anterior slide. The quadriceps muscle is often referred to as the “ACL antagonist”, since it directly opposes the ACL’s restraint of anterior tibial glide. In order to determine if the ACL is lax or ruptured following on injury, clinicians may perform the anterior drawer test (along with other special tests): with the knee flexed to 90 degrees and the foot fixed, the clinician applies a direct, firm, posterior-to-anterior force to the tibia. If anterior translation of the tibia on the femur is increased relative to the uninvolved knee, this result is highly suggestive of an ACL tear. The ACL is most taut in a position of terminal knee extension, as shown in Figure 39B; this allows the ACL to stabilize the knee during weight-bearing activities in which the knee is relatively extended. However, some fibers of the ACL are taut at any given point in the arc of motion. This property of the ligament arises from its unique double-bundle configuration: the ACL is formed from two distinct fiber groupings, the anteromedial and posterolateral bundles, which are named according to their tibial attachments. These bundles have different fiber orientations and therefore different lines of pull, which permits the ACL to resist anterior tibial translation throughout knee extension. Additionally, the oblique orientation of the entire ACL unit enables it to resist axial rotation and valgus forces. The PCL also has two primary fiber groups, the anterolateral and posteromedial bundles. The PCL is most taut in a position of 90 – 120 degrees of knee flexion, but, as in the ACL, the opposing orientation of these bundles allows some fibers to remain taut throughout both flexion (the anterolateral bundle) and extension (the posteromedial bundle). The oblique orientation of the PCL unit also allows it to resist tibial rotation and both varus and valgus loads. Figure 36: Ligamentous Structures of the Knee
  • 44. 43 Figure 39: Intra-articular Ligaments of the Tibiofemoral Joint, on slack (A) and under tension (B) Figure 38: Posterior Slide of Tibia on Femur The primary role of the posterior cruciate ligament is to limit posterior shear of the tibia on the femur, as occurs as the knee approaches full flexion in the open kinetic chain (Fig. 38). As knee moves into 90 degrees of flexion, the contraction of the hamstrings pulls the tibia posteriorly on the femur. As the PCL becomes taut, it helps limit the extent of this posterior slide. Much like the quadriceps, the hamstring muscles are often referred to as the “PCL antagonist”, as they directly oppose the PCL’s restraint of posterior tibial glide. The posterior drawer test allows clinicians to assess the integrity of the PCL. This test is identical to the anterior drawer, with the obvious exception that the force applied to the tibia is directed from anterior to posterior. The collateral ligaments are broad, thick structures running along the medial and lateral aspects of the knee. The medial collateral ligament (MCL) consists of superficial and deep parts divided by a bursa (Fig. 36). The superficial portion of the MCL is most taut when the knee is extended (Fig. 39B), and it functions primarily to resist valgus forces. The deep portion is continuous with the joint capsule and is secured to the medial meniscus; it does not play a significant role in resisting valgus forces at the knee. When the knee is fully extended, the capsule, pes anserine, and the ACL also contribute to the resistance of valgus forces applied to the extended knee. When the knee is flexed to 20 – 30 degrees, these structures become less involved, making the MCL the primary resistance to help limit valgus force. The MCL also works in synergy with the ACL to limit anterior shearing of the tibia on the femur. If the MCL is ruptured, however, the ACL becomes the only ligament resisting anterior shear, and is therefore subjected to increased stress. Fortunately, unlike the cruciate ligaments, MCL has a robust blood supply and is much more likely to heal on its own.
  • 45. 44 Fig. 40: Extracapsular Ligaments of the Lateral Knee The lateral collateral ligament (LCL) is a strong, round band; its distal portion blends with the biceps femoris tendon. It is an extracapsular structure, and unlike the MCL, it does not attach directly to its corresponding (lateral) meniscus. The LCL primarily resists varus forces at the knee. Similar to the MCL, the LCL is most taut in extension, due to its position slightly posterior to the medial-lateral axis of the knee. However, the LCL fulfills its primary function (as the principle resistor of varus force) when the knee is slightly flexed. In addition to the extracapsular collateral ligaments, the anterolateral ligament (ALL) has recently been recognized as an independent extracapsular ligament of the knee. Its proximal attachment lies near that of the LCL, but it attaches distally to the anterolateral surface of the tibial plateau (Fig. 40). Its primary role is to provide rotational stability; therefore, damage to the ALL places the knee at increased risk for injury during rotatory movements. The ALL also resists varus forces at the knee, and it is most taut in extension. The two menisci of the tibiofemoral joint are attached to the tibial plateau. The medial and lateral menisci are crescent-shaped, fibrocartilaginous structures that form shallow “seats” for the large convex femoral condyles, thus stabilizing their articulation with the tibial plateau. This soft tissue adaptation is most important at the lateral tibial condyle due to the slightly convex shape of this articular surface. The anterior and posterior horns of the menisci anchor them to the intercondylar region of the tibia. A slender transverse ligament joins the medial and lateral menisci anteriorly. The coronary ligaments connect the external edge of each meniscus to the medial and lateral surfaces of the tibial plateau; they are relatively loose to allow for rotatory motion at the knee. Various muscles also attach to the menisci to help stabilize them during joint motion. For instance, the quadriceps and semimembranosus muscles attach to both menisci; the popliteus muscles attaches to only the lateral meniscus. As stated previously, the medial meniscus attaches directly to the MCL, whereas the external border of the lateral meniscus attaches to the lateral joint capsule. Capillaries within the synovial membrane supply the outer two-thirds of the menisci. The blood supply diminishes significantly as it travels deep into the
  • 46. 45 Fig. 41: Menisci of the Tibiofemoral Joint joint space; consequently, the inner one-third of each meniscus is functionally avascular which prevents the healing process. The primary function of the menisci is to reduce compressive forces within the tibiofemoral joint by dispersing the forces over a larger surface area. This is a critical function for preserving joint health, as these compressive forces average 2.5 – 3 times the force of body weight during ambulation; they increase to almost 4 times body weight while ascending stairs. Studies have shown that a complete lateral meniscectomy increases the contact pressures within the tibiofemoral joint by 230 percent. This intensification of intra-articular pressure ultimately increases an individual’s risk for developing stress-related arthritis and significant knee pain. Even an incomplete tear in either meniscus leads to an increase in local stress and wear on the articular cartilage. The menisci are therefore integral to the health and longevity of the tibiofemoral joint. Other secondary functions of the menisci include providing the CNS with proprioceptive feedback, stabilizing the joint during motion, lubricating the articular cartilage, and guiding the arthrokinematics of the knee. The O-shaped lateral meniscus covers a larger area of the tibial plateau than does the C-shaped medial meniscus (Fig. 41). However, the majority of compressive forces act upon the medial compartment of the knee, placing greater stress on the medial joint surface and meniscus. The lateral meniscus is less strongly adhered to the tibial plateau and is therefore more mobile than its medial counterpart. Joint Configuration of the Tibiofemoral Joint The femoral condyles are convex surfaces and the tibial plateau is primarily concave. As stated above, the lateral tibial plateau is slightly convex, but the lateral meniscus creates a concave surface to allow the lateral femoral condyle can move more smoothly. During weight bearing (closed-chain) activities, the convex femoral condyles move on the concave tibial plateau. During non-weight bearing (open-chain activities), the concave tibial plateau moves on the convex femoral condyles. Tibiofemoral arthrokinematics in the sagittal plane occur via rolls and glides. As the knee moves into extension during closed chain activity, the femur rolls anteriorly and glides posteriorly to fit onto the tibial plateau. Conversely, as the knee moves to flexion during closed chain activity, the femur rolls posteriorly and glides anteriorly. In open chain extension, the tibia rolls anteriorly and glides anteriorly to properly articulate with the femoral condyles. In open
  • 47. 46 Fig. 42: Tibiofemoral Arthrokinematics in the Open (A) and Closed (B) Chains chain flexion, the tibia rolls and glides posteriorly. These interactions are illustrated in Figure 42. Arthrokinematics in the transverse plane occur via spinning (axial rotation) of the moving articular surface on the stable surface. In the open chain, external rotation of the knee occurs via external rotation of the tibia on the femur and internal rotation of the knee is driven by internal rotation of the tibia on the femur. Thus, the relationship between tibial and total knee rotation is direct. The reverse occurs in the closed chain: external rotation of the knee occurs by internal rotation of the femur on the tibia and internal rotation of the knee occurs by external rotation of the femur on the tibia. This represents an indirect relationship between femoral and total knee rotation. As noted earlier, axial rotation is only available when the knee is in some flexion; rotational range of motion increases with greater knee flexion. Apparently similar to, through functionally different from axial rotation in the transverse plane, the “screw-home” mechanism describes the rotation of the tibiofemoral joint that occurs during the last 30 degrees of extension in order to “lock” the joint into place/ Screw-home rotation is a conjunct movement that cannot be performed independently of physiologic flexion and extension. This mechanism can occur during both open and closed chain activities. In non-weight bearing positions, the tibia externally rotates on the femur to “lock” the knee in terminal extension and must internally rotate to “unlock” the tibia towards flexion. While weight-bearing, the femur must internally rotate on the tibia to “lock” the knee in terminal extension and must externally rotate to “unlock” the femur into flexion. The screw-home mechanism can be affected by the following three factors: the shape of the medial femoral condyle, the passive tension in the ACL, and the lateral pull of the quadriceps muscle. The shape of the medial femoral condyle affects the screw-home mechanism the most significantly. The medial femoral condyle extends further anteriorly than does the lateral femoral condyle; therefore, the moving tibia must curve around this projection. As the femur rolls anteriorly and glides posteriorly during closed chain extension, it deviates medially, thus internally rotating on the stable tibia to create the “locking” mechanism. During open chain extension, as the tibia rolls and glides anteriorly, it deviates slightly lateral to the medial femoral condyle, thereby externally rotating on the stable femur in order to “lock”. To “unlock” the knee, the articular surfaces of the tibia must glide back to their neutral alignment in the intercondylar
  • 48. 47 groove. The popliteus muscle also assists in “unlocking” the knee: its muscle action opposes the screw-home mechanism. Table 11: Ligaments of the Tibiofemoral Joint Ligament Proximal attachment Distal attachment Function Associated constraints of tibiofemoral joint Anterior cruciate (ACL) Medial side of lateral femoral condyle Anterior intercondylar area of tibia Stabilization in the sagittal and transverse planes Open chain: anterior translation of tibia on femur Closed chain: posterior translation of femur on tibia Knee extension Extreme axial rotation Extreme varus/valgus force Posterior cruciate (PCL) Lateral side of medial femoral condyle Posterior intercondylar area of tibia Stabilization in the sagittal plane Open chain: posterior translation of tibia on femur Closed chain: anterior translation of femur on tibia Knee flexion Extreme axial rotation Extreme varus/valgus force Medial collateral (MCL) (see below) (see below) Limits valgus force Stabilization of knee, especially in extension and end-range Valgus force Knee extension End-range axial rotation (external rotation)
  • 49. 48 external rotation MCL superficial Medial epicondyle of femur Medial-proximal part of tibia More rotational force (external rotation) Tibial external rotation MCL deep Deep, posterior, and distal to superficial fibers Posterior-medial joint capsule, semimembranos us tendon, medial meniscus More valgus force Genu valgum Lateral collateral (LCL) Lateral epicondyle of femur Head of fibula Stabilization of the lateral knee Varus force Knee extension End-range axial rotation Anterolatera l (ALL) Proximal and posterior to lateral femoral epicondyle Lateral tibial plateau between head of fibula and Gerdy’s tubercle Taut with knee extension (0-60 degrees) and internal rotation Varus force Transverse Connects the medial and lateral menisci Posterior Oblique Posterior to adductor tubercle and anterior to gastrocnemius tubercle on femur Distal and posterior to distal attachment of superficial MCL on tibia Reinforces posterior capsule, especially posteromedial corner Oblique popliteal Adjacent to postero- superior area of lateral femoral Posteromedial capsule and semimembranos us tendon Reinforces posterior capsule, especially posteromedial Knee external rotation
  • 50. 49 condyle corner Arcuate popliteal Two heads: 1. Posterior intercondylar area of tibia 2. Posterior side of lateral femoral condyle Fibular head Reinforces posterior capsule, especially posterolateral corner Coronary External edges of menisci Tibial edge and nearby capsule Attaches the menisci to the tibia Meniscofem oral May assist stabilization of the lateral meniscus of posterior horn · Meniscofem oral posterior Femur posteromedial to PCL Lateral meniscus posterior horn · Meniscofem oral anterior Femur anterior to PCL Lateral meniscus posterior horn Common Tibiofemoral Joint Pathology The ACL is the most commonly torn ligament tear of the knee. ACL ruptures are much more common in females compared to males primarily due to the anatomical structure of the female pelvis and lower extremity: females typically have a wider pelvis, a larger Q-angle, increased range into knee extension, a narrower femoral notch, and less developed thigh musculature, all of which increase susceptibility to ACL injury. An ACL tear occurs when the tibia is displaced anteriorly on the femur to such an extreme that tensile stress on the ACL exceeds the capacity to resist. Common mechanisms of injury include a non-contact rotational force at the knee, hyperextension, poor biomechanics when landing a jump, or a direct blow to the lateral side of the knee which generates a valgus stress. The ACL is rarely injured in open-
  • 51. 50 Figure 43: Osteoarthritis of the Knee chain movements. Often times the patient will report hearing a “pop” or state that the knee “gave way” at the time of injury, and describe onset of swelling immediately after the event. Many ACL injuries also involve damage of other local structures, including the MCL, the menisci, and the knee joint capsule. Since the ACL is an intracapsular structure and does not heal well independently, ruptures are often treated surgically by using autographs of the patient’s patellar or hamstring tendon or cadaveric allografts to replace the native ACL. Meniscal tears are also quite common. They can be classified as acute (sudden onset), chronic (typically in patients older than 50 years of age with no specific injurious event to report), or degenerative (associated with arthritis). Common mechanisms of injury include forced axial rotation or an external valgus force (such as occurs in a blow to the lateral aspect of the knee) in closed-chain movements. The individual may report hearing a “pop” and a slow onset of effusion; these patients often present with tenderness to palpation along the joint line. The location of the tear can help determine the patient’s prognosis. The the outer 1/3 of the meniscus (the “red-red zone”) receives substantial blood supply. A tear in the red-red zone has the best prognosis and a good potential for healing. If the tear is in the middle 1/3 of the meniscus (the “red- white zone”), the prognosis is more guarded, though there may be some healing potential due to moderate blood supply to this area. The white-white zone is the inner 1/3 of the meniscus and does not receive any blood supply: a tear in this zone has the worst prognosis and is unlikely heal. Meniscal tears may benefit from conservative management including a temporary change in activity and use of NSAIDs for control of inflammation. If the meniscus does not heal and swelling and pain still persist after one month of conservative management, the individual may need surgery. Surgery can consist of a partial or complete meniscectomy; however, meniscectomies are no longer recommended due to the risk of developing osteoarthritis. Another option for surgery could be a meniscal repair for a tear in the red-red zone. Osteoarthritis of the knee occurs when there is decreased intra-articular space between the femur and tibia. This typically occurs when the menisci are progressively worn or when there is eroding of the articular cartilage of the femoral condyles. Both situations lead to bone-on-bone contact, which can result in the formation of bone spurs (Fig. 43). The elderly are more prone to this progressive degenerative joint disease. Other factors that can lead to osteoarthritis include increased weight bearing through the meniscus (as in cases of obesity), a previous injury to the tibiofemoral joint, or inappropriate loading through the joint due to genu varus or valgus position. Common complaints from individuals with osteoarthritis include pain, morning stiffness, and/or difficulty fully flexing or extending the knee secondary to stiffness or edema.
  • 52. 51 Management of osteoarthritis can vary, but the most common final treatment is a total knee arthroplasty to replace the joint surfaces with metal or plastic. The Patellofemoral Joint The patellofemoral joint is formed by the articulation of the patella, the largest sesamoid bone in the body, with the intercondylar groove of the femur. The patella is embedded within the quadriceps tendon and attaches to the tibial tuberosity of the tibia. Neurovascular supply to this joint was described previously. Stability of the joint is provided by the quadriceps muscles, the structure of the joint surfaces, and the surrounding retinacular fibers of the joint capsule. Table 12: Physiologic Motions of the Patellofemoral Joint and the Associated Muscles Motion Primary Associated Muscles Secondary Associated Muscles Superior Glide (associated with knee extension) Quadriceps (rectus femoris, vastus lateralis, vastus medialis, vastus intermedius) N/A Inferior Glide (associated with knee flexion) Eccentric motion of the quadriceps Hamstrings (biceps femoris, semimembranosus, semitendinosus) Biomechanics and Kinematics of the Patellofemoral Joint The biomechanics and kinematics of the patellofemoral joint vary throughout flexion and extension of the knee. At rest, the patella lies slightly inferior to the suprapatellar fat pad. When the knee is flexed to approximately 135 degrees, the superior pole of the patella is the primary point of contact with the femur. As the knee extends to a 90 degree angle, this primary contact point begins to migrate inferiorly. While the surface area of contact between the patella and femur is the largest in this position, the total contact area still only involves one-third of the posterior patellar surface. At 20 degrees of knee flexion, the inferior pole of the patella is its primary point of contact with the femur; the patella now articulates only very slightly with the intercondylar groove of the femur. The black circle in each panel of Figure 44 illustrates the point of maximal contact between the patella and the femur in each of these positions. The
  • 53. 52 Figure 44: Biomechanics of the PatellaFigure 45: Forces Acting on the Patella patella is most stable within the intercondylar groove of the femur when the knee is flexed between 60 - 90 degrees. When the knee is in full extension (and the quadriceps are relaxed), the patella can be moved freely relative to the femur. Since the patella is imperfectly congruent with the femur, it requires many other structures to maintain stability. One of the primary stabilizers is the quadriceps muscle group, which also significantly influences the tracking of the patella. During knee extension, the contraction of the quadriceps muscle primarily pulls the patella superiorly, then slightly laterally and posteriorly into the intercondylar groove. The iliotibial band and lateral patellar retinacular fibers supplement this lateral pull on the patella (Figure 45). To quantify the amount of lateral pull on the patella, a Q-angle can be measured. Activation of the oblique fibers of the vastus medialis and the medial patellar retinacular fibers help counteract this pull. The medial patellar retinacular fibers contain the medial patellofemoral ligament: this ligament forms the thickest portion of the retinaculum and provides the strongest restraint against the lateral pull of the quadriceps. Even though all of these muscles and ligaments have a significant impact on patellar biomechanics, the most crucial resistance to the lateral pull itself is the lateral femoral condyle itself. The slope of the lateral condyle is steeper than that of the medial condyle, allowing to promote proper patellar tracking within the groove. Individuals with a small lateral femoral condyle and a shallow intercondylar groove are more susceptible to patellar dislocation and/or subluxation.