This document provides an overview of the biomechanics of the knee complex. It describes the knee as the largest and most complex joint, consisting of the tibiofemoral and patellofemoral joints. The knee functions to flex and extend the leg, support body weight, and facilitate locomotion. Key components include the articular surfaces, menisci, capsule, collateral and cruciate ligaments, muscles, bursae, and plicae. The document outlines the roles and mechanics of each of these structures, as well as common injuries associated with the knee.

1. Biomechanics of
Knee Complex
BPT Year 1 Semester 2
Lecture 1

2. Contents
1. Introduction
2. Function
3. Tibio-femoral joint and Patellofemoral joint
4. Articular surfaces
5. Capsule, ligaments and Menisci
6. Muscles around the knee
2

3. Introduction
 Largest and one of the most complex joints
 Major stability and mobility roles
3

4. Functions:
 Functional shortening and lengthening of the
extremity by flexion and extension
 Supports body during dynamic and static activities
 Closed kinematic chain- support body weight in
static erect posture
 Dynamically- moving and supporting body in
sitting and squatting activities, supporting and
weight transferring activity during locomotion
4

5. Knee complex
Tibio- femoral Patello-femoral
5

6. Tibio-femoral Joint
 Type of Joint?
 Double Condyloid joint
 Degrees of freedom of
motion?
 Flexion/ Extension
 Medial/ Lateral rotation
 Adduction/ abduction
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7. Articular surfaces

8. Articular surfaces
Proximal Articular Surface:
 femoral condyles
 Medial condyle larger than lateral
Distal Articular Surface:
Tibial condyles- medial and lateral
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9. Alignment of knee
• The Anatomical axis of
femur is oblique directed
inferiorly and medially.
• Anatomical axis of tibia is
vertical.
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10. Alignment of knee
 Normally knee forms lateral
angle of 170o-175o
Variation:
 Genu valgum or Knock knee-
lateral angle < 170o
 Genu vaRum or bow leg-
angle > 180o
10
Neumann, 2010

11. Alignment of knee
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12. Menisci
Fibrocartilagenous disc
Functions
Blood supply
Mechanism of injury

13. Menisci: Functions
 Improves congruence of joint
 Distributes weight bearing forces
 Decreases friction between tibia and femur
 Shock absorber
13

14. Nutrition
 First year of life: contains blood vessels
throughout meniscal body
 Vascularity decreases with age
 Outer 25% is vasularized by capillaries from
joint capsule and synovial membrane
 Central blood supply by diffusion from
synovial fluid
14

15. Prolonged immobilization or
non-weight bearing?
 Menisci does not receive appropriate nutrition
 Avascular nature of central portion of meniscus
reduces potential of healing after injury
 In adults only peripheral portion of meniscus is
vasularized hence is capable of inflammation,
repair and remodeling after injury or tear.
15

16. Compression forces at the knee:
 While walking- 2.5 – 3 times body weight
 Ascending stairs: 4 times
 Menisci triples the surface area by significantly
reducing the pressure on the articular cartilage
 Lateral menisectomy increases pressure at knee
by 230%
16
Neumann, 2010

17. Mechanisms of meniscal injury
 Forceful, rotation of femoral condyle on partially
flexed and weight bearing knee
 locked knee syndrome
 Medial meniscus is injured twice as much as
lateral
 Risk of meniscal injury increases with instability
17

18. Test for Miniscal injury
 Apley’s Grinding Test
 McMurray’s Test
18

19. 19

20. • Capsule
• Collateral Ligament
• Cruciate ligament
20
Capsule and Ligaments

21. Capsule
 Encloses medial and lateral tibio-femoral joint
and patello-femoral joint.
 Two layers of capsule: Fibrous layer
Synovial layer
21

22. Capsule:
Fibrous layer
 Three layers:
1. Extensor retinaculum: anteriorly
2. Fascial layer: distal quadriceps muscle
3. Deep: medial and lateral retinacula
22

23. Capsule:
Synovial layer
 Internal surface of the capsule is lined by
synovial membrane.
 Role:
1. secretion of synovial fluid
2. Absorption of fluid into joint for lubrication
3. Nutrition to avascular structure like menisci
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24. MCL
LCL
Collateral ligaments

25. Medial collateral ligament (MCL)
• Originates from medial
epicondyle of femur
• Inserted into medial tibial
plateau, medial
meniscus, medial
proximal tibia.
• Restrains excess
abduction and lateral
rotation stress at knee
25

26. MCL: Applied aspect
 Injury when valgus stress is
delivered over a planted foot.
 Common in football players
 MCL is rich in blood supply hence
has good healing
26

27. Lateral collateral ligament (LCL)
27
 Extracapsular
 Origin: Lateral femoral
condyle
 Insertion: fibular head
 Checks Varus stress
and excessive lateral
rotation of tibia

28. Anterior cruciate ligament
Posterior cruciate ligament
Cruciate ligaments

29. 29

30. Anterior Cruciate Ligament
30
 Inferior attachment: anterior tibial spine
 Extends superiorly, posteriorly to attach to the
postero-medial aspect of the lateral femoral
condyle
 Two bands:
 Anteromedial band (AMB)- taut in flexion
 Postero-lateral band (PLB)- taut in extension

31. Anterior Cruciate Ligament
31
 Functions:
 Restrains anterior translation of tibia on femur
 Prevents hyperextension of knee
 Secondary restraint against varus and valgus
motion

32. Mechanism of injury- ACL
 Most common injury
 Football, downhill skiing, basketball and soccer
players
 Mechanism:
 Common in weight bearing, slight flexion and
rotation in either directions
 Anterior translatory force on proximal tibia
 Hyperextension injury
 Hyperflexion in bulky lower extremity muscles
32

33. Posterior Cruciate Ligament
33
• Origin: Posterior inter-condylar area of tibia
• Insertion: Lateral side of Medial femoral
condyle
• Anteromedial and posterolateral bands

34. Functions- PCL
 Primary restraint to posterior translation of
tibia on femur
 Limits the anterior translation of femur over
fixed tibia in activities such as rapid
descending into squat and landing from jump
with partially flexed knee
34

35. Mechanism of injury- PCL
 Three mechanisms
1. Pretibial trauma (Dashboard trauma)
2. Hyper flexion (in thin individual)
3. Hyperextension (second ligament to be
injured after ACL)
35

36. Muscles Aiding Tibial Translation
 Anterior Translation:
1. Quadriceps
2. Gastrocnemius
 Posterior Translation:
1. Soleus
2. Hamstring
36

37. Other ligaments
 Oblique popliteal ligament
 Anterolateral ligament (newer ligament)
List out all other ligaments and its function
referring to articles and reference text books
37

38. Bursae

39. Bursae
 14 bursae
 Reduce friction between intertissue junction
during movement.
 Activities that involve excess and repetitive
force at inter tissue junctions frequently leads
to Bursitis.
40

40. Bursae
41
 Suprapatellar
 Prepatellar
(Housemaid’s
knee)
 Infrapatellar
(Clergyman’s knee)

41. Bursitis
42
Prepatellar bursitis
(housemaid’s knee)
 Infrapatellar bursitis
(clergyman’s knee)

42. Plicae

43. Plicae
Synovial membrane formation occurs in early
embryonic development
Synovial membrane separates medial and lateral
articular surface into separate cavities
By 12th week of gestation synovial septae
reabsorbs to form a single joint cavity
44

44. Plicae
Failure of complete resorption results in
persistent folds called PLICAE
Plicae may get inflamed or irritated-
Plicae Syndrome
45

45. Summary
 Articular components
 Menisci
 Capsule
MCL, LCL, ACL, PCL
 Ligaments
 Bursae
 Plicae
46

46. References:
 Neumann DA. Kinesology of musculoskeletal
system, Foundation for Physical Rehabilitation ,
2nd Edition
 Norkin C, Levengie P. Joint structure and
function. 4th Edition
 Kapandji IA. The Physiology of Joints. Volume 2,
Lower Limb. 5th Edition
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