ComPLETE biomechanic of knee joint

1. BIOMECHANICS
OF KNEE JONT
AKSHAY CHAVAN
MPO 1st YEAR
A.I.I.P.M.R. MUMBAI

2. • Knee joint complex
• Biomechanical role in
stability
• Patella
• Kinematics
1) Osteokinematics
2) Arthrokinematics
• Kinetics
Will Be Discussed

3. Knee joint complex
• Largest joint, complex joint.
• Synovial joint of the hinge variety.
• Allow locomotion .
• Minimum energy requirements.
• Transmit, absorb and redistribute forces.
• Stability v/s Mobility.

4. Structure of knee joint

5. BIOMECHANICAL ROLES
TIBIAFEMUR
the medial femoral condyle being approximately 1.7 cm longer than the lateral femoral
condyle.

6. Meniscus
• 2 asymmetrical fibro cartilaginous joint disk .
• Thick peripherally, Thin centrally forming cavities for femoral condyle.
• serve as shock absorber.

7. COLLATERAL LIGAMENTS
Medial Collateral Ligament
Origin – medial aspect of medial femoral condyle
Insertion – proximal tibia.
• Resist valgus stress force (specially in extended
knee)
• Check lateral rotation of tibia
• Also restrain anterior displacement of tibia when
ACL is absent.
Lateral Collateral Ligament
Origin – lateral femoral condyle
Insertion – posteriorly to head of fibula.
• Resist Varus stress force across the knee
• Check combined lateral rotation with
posterior displacement of tibia in
conjunction with tendon of popliteal
muscle.

8. CRUCIATE LIGAMENTS
Cruciate ligament are Intracapsular Ligaments and provide stability in sagittal plane .
ANTERIOR CRUCIATE LIGAMENT
Origin – from anterior surface the tibia in the
intercondylar notch just medial to medial meniscus.
Insertion– to posteriorly on lateral condyle of femur
• femur from being displaced posteriorly on the
tibia
• preventing excessive hyperextension of the knee
• Check Tibial medial rotation
POSTERIOR CRUCIATE LIGAMENT
Origin – from posterior tibia in intercondylar area and
runs in a superior and anterior direction on medial
side of ACL.
Insertion - to anterior femur on the medial condyle
• prevents posterior displacement of tibia over fixed
femur
• It tightens during flexion
• Check Tibial lateral rotation

9. STABILITY OF KNEE JOINT
INTRINSIC STABILITY
• anterior cruciate ligament (ACL)
• The posterior cruciate ligament
(PCL)
• Medial collateral ligament
• Lateral collateral ligament
• patellar ligament
EXTRINSIC STABILITY
• Provided by muscles
• Extensors : Quadriceps femoris
• Flexors : hamstrings,
gastrocnemius

10. PATELLA
The triangular shape patella is a largest sesamoid bone in body.
• Patella is an anatomical pulley system.
• Lengthening of the lever arm of quadriceps muscle force.
• Aids knee extension by producing anterior displacement of quadriceps tendon
through the entire ROM
• It reduce friction between quadriceps tendon & femoral condyle.
• The ability of patella to perform its function without restricting knee motion depends
on its mobility.

12. STABILITY
• Transvers group of stabilizer
• Longitudinal group of stabilizer
Transvers stabilizer
• Medial & lateral retinaculum
• Vastus Medialis & Lateralis
• The lateral PF ligament
contributes 53% of total force
when in full extension of knee.
Longitudinal stabilizer
• Patellar tendon – inferiorly
• Quadriceps tendon – superiorly

13. Kinematics - Osteokinematics
• 6 degrees of freedom
• 3 rotations
• 3 translations
SYNOVIAL BICONDYLAR- HINGE ARTHODIAL

14. Translation:
• Anterior-posterior: 5–10 Mm
• Compression: 2–5 Mm
• Medio-lateral: 1-2 Mm
Rotation:
• Flexion-extension: Up To 140 Deg Of Flexion
(Up To -5 Deg Flexion – Hyperextension)
• Varus-valgus: 6-8 Deg In Extension
• Internal-external Rotation: 25-30 Deg during Flexion
RANGE OF MOTION

15. Kinematics - Arthrokinematics
Femur Motion During Flexion-extension
1st 30 degree - mainly roll >30 degree roll and anterior glide

16. • Functional range of motion
(ROM) at the knee
Activities Knee flexion
• Normal gait/level 50- 60°
surfaces
• Stair climbing 65- 80°
• Sitting/rising from 90° most
chairs
• Sitting/rising from toilet seat
115º
• Advanced function > 115°
What is ICR and how to locate ?

17. Internal-external Rotation
“Screw-Home” mechanism
• Rotation between the tibia and femur.
• initial phase of flexion (unlocking) and the final 30° of extension
(locking).
• medial femoral condyle being approximately 1.7 cm longer than the
lateral femoral condyle.
• Internal rotation takes place during knee flexion and external rotation
occurs during knee extension.
• Larger medial femoral condyle continue rolling & gliding posteriorly
when smaller lateral side stopped.
• The medial rotation of femur at final stage of extension is not voluntary
or produce by muscular force, which is referred as “Automatic” or
“Terminal Rotation”.
• The rotation within the joint bring the joint into a closed packed or
Locked position.
• The consequences of automatic rotation is also known as “Locking
Mechanism” or “Screw Home Mechanism”.

18. • The twisting of cruciate ligaments play an important role in the screw home
mechanism of the knee which promotes locking and unlocking of the knee joint.
It is considered a key element to knee stability for standing upright.
• Tibia rolls anteriorly, on the femur, PCL Elongates.
• PCL's pull on tibia causes it to glide anteriorly.
• Anterior Tibial glide persists on the tibia's medial condyle because its
articular surface is longer in that dimension than the lateral condyle's
• Prolonged anterior glide on the medial side produces external Tibial rotation.
 Tibia rolls posterior, elongating ACL.
 ACL's pull on tibia causes it to glide Posterior.
 Relative Tibial internal rotation.
 A reversal of the screw - home mechanism.

19. HELFET TEST clinical test to determine screw home
mechanism of the knee is intact

20. Meniscus Movement During Screw
Home Mechanism

22. Patellofemoral Joint
• Motion occurs in two planes: Frontal and transverse
• At full extension both medial and lateral femoral facet articulate
with the patella.
• More than 90degrees of flexion the patella rotate externally, and
only the medial femoral facet articulate with the patella
• At full flexion patella sinks into intercondylar groove.

24. KINETICS OF KNEE JOINT
• It is the study of forces and moments acting on a joint in equilibrium.
• So static analysis is carried out when either no motion takes place or at one
instant during dynamic activity ( like walking or running)
• Statics, Dynamics, Equilibrium, Translatory, Rotatory equilibrium
Free Body Technique The steps are as follows
• The minimum magnitude of forces and moments are obtained.
• The portion to be analyzed is isolated ( in this case it is the knee
joint)
• All the forces acting on the body are identified
• A free body diagram is drawn in loading situations
• The forces are designated as vectors on the diagram. Vectors have
four principle characteristics which must be identified. Those are :
• Magnitude
• Sense
• Line of application
• Point of application

25. F
W
ab
p
Three main coplanar forces are identified which are also concurrent i.e. they
intersect at one point
w - ground reaction force
a - perpendicular distance for w
p - force at patella
b - perpendicular distance for p

26. Dynamic Analysis Of Knee joint
• It is the analysis of forces and moments acting on a body in
motion.
• The following act on the knee joint during dynamic activity.
• Steps for calculating minimum magnitudes of force at a particular
instant :
• Identify the anatomical structures responsible for production of
force.
• Determine the angular acceleration of the part of the body in
motion.
• determine the mass moment of inertia of the moving body part
• Thus, calculate the torque about the joint.
• I x a = T
• The magnitude of the main muscle force is P is obtained
• Magnitude of joint reaction of force is F and is obtained by the
equation T=F x d

28. Patellar tendon compression force
Activity Force % Body weight
Walking 850 N 1/2 x BW
Bike 850 N 1/2 x BW
Stair ascend 1500 N 3.3 x BW
Stair descend 4000 N 5 x BW
Jogging 5000 N 7 x BW
Squatting 5000 N 7 x BW

29. ANY QUESTION ?????

30. THANK YOU