Pathomechanics Knee.pptx

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1. Pathomechanics of Knee Joint Dr. Venkat Singh (PT) MPT (ORTHO)

2. Knee Complex The knee is a complex joint formed of Tibiofemoral Joint : Articulates between distal femur & proximal tibia. Patellofemoral Joint : Articulates between posterior patella and anterior distal part of femur. It is bicondylar type of synovial joint.

3. What does Pathomechanics means? It is defined as the mechanics of living systems in motion resulting in, or leading to, dysfunction or injury. Brown, L. P., & Yavorsky, P. (1987). Locomotor biomechanics and pathomechanics: a review.  The Journal of orthopaedic and sports physical therapy ,  9 (1), 3–10. https://doi.org/10.2519/jospt.1987.9.1.3

4. Screw Home Mechanism Screw home mechanism of Knee Joint is a critical mechanism that play an important role in terminal extension of the knee. There is an observable rotation of the knee during flexion and extension. In tibiofemoral extension: the tibia externally rotates about 10 degrees.  In femorotibial extension(rising from squat): The femur internally rotates on fixed tibia. Regardless whether leg or femur is moving the knee is externally rotated 10 degrees when fully extended.

5. To observe Screw Home Mechanism  At the knee: have the person sit with the knee flexed to about 90 degrees. Draw a line on the skin between the tibialtuberosity and the apex of the patella. After completing full tibial –on femoral extension, redraw this line between the same landmarks and note the change in position of the externally rotated tibia.

6. Unlocking Mechanism  To unlock the knee that is fully extended, the joint must first internally rotate by popliteus muscle that is both internal rotator and flexor of the knee joint, the muscle can rotate femur externally to initiate femoral-on tibial. Flexion or rotate the tibia internally to initiate tiabial on- femoral flexion. As the extended and locked knee prepares to flex (e.g. when beginning to descend into a squat position), the popliteus provides an internal rotation torque that help mechanically to unlock the knee. In this position the femur is externally rotated on tibia , this action on femur is readily seen by this figure showing line of pull of popliteus

7. Factors Guiding Screw Home Mechanism 1. Shape of medial femoral condyles: as it curves 30 degree laterally as it approaches the intercondylar grove. And as and extends further anteriorly than the lateral condyle. Thus tibia must follow this path during tibial on femoral extension. 2. Passive tension in the anterior cruciate ligament 3. Lateral pull of quadriceps tendon.

8. Common Knee Abnormalities #Changes Frontal plane knee joint alignment : Normal Tibiofemoral angle: normal alignment is distal end of femur makes an angle of 180 -185° with the mechanical axis. Tibiofemoral Angle 180-185°

9. Genu Valgum : The medial condyle is enlarged and the lateral condyle is diminished and flattened. Effects of Genu valgum: -The weight bearing line is placed on the outer side of the knee effects -Strain on medial collateral ligament. -Osteoarthritis in later stages. Angle more than 185°

10. Genu Varum: When angle is 175° or less  There is deflection in the axis of tibia in varus and inward in relation to the femur. Effects of genu varum: -The subtalar joint goes into inversion to adapt the sole on the ground. -Strain on the lateral collateral ligament -Osteoarthritis in later stages.

11. #Changes Sagital plane knee joint alignment : Genu Recurvatum: Hyperextension beyond 10 degrees of neutral is frequently called genu recurvatum. Mild cases of recurvatum may occur in otherwise healthy persons, often because of generalized laxity of the posterior structures of the knee. The primary cause of more severe genu recurvatum is a chronic, overpowering (net) knee extensor torque that eventually overstretches the posterior structures of the knee.

12. Meniscus Medial and lateral meniscus are fibro-cartilaginous discs that deepen the shallow articular surface of tibia by acting as seats or cushions to femoral condyles. Medial meniscus is C shaped while lateral meniscus is 0 shaped.

13. Function of Meniscus 1-Reduce the huge compressive stress at the tibio-femoral joint that may reach 2-3 times body weight during routine knee activity. 2- Stabilizing the joint during motion. 3-Lubricating the articular cartilage. 4-Reducing friction.

14. Attachment of Meniscus:   1- Each other anteriorly, 2- Tibial plateau, 3- Femoral condyles, 4- Joint capsule, 5- Quadriceps, semimembrenosus. Additionally medial meniscus is attached to medial collateral ligament, lateral meniscus is attached to popliteus muscle.

15. Medial Meniscus: The medial meniscus is more frequently injured more than lateral meniscus because its attachment to the medial collateral ligaments. As medial meniscus movements are more limited than lateral meniscus movements Common Mechanism of meniscus tear: Tears of menisci often occurs by forceful horizontal plane rotations of the femoral condyles over a partially weight bearing flexed knee.

16. A classic complaint of an individual with a meniscal tear (dislodged or flap meniscus) is that the joint locks when he or she attempts to extend the knee from a position of weight bearing, such as rising from a seated position or climbing stairs.

17. Collateral Ligament Injury The medial collateral ligament (MCL): It is a flat, board structure that spans the medial side of the joint. It resist valgus stress (abduction), extension, and extreme axial rotations. Common Mechanism of injury: 1-Valgus force with foot planted. 2- severe hyperextension injury of knee.

18. Lateral Collateral Ligament:  It is a round strong cord that runs nearly vertical between the lateral epicondyle and head of fibula. It resist varus stress (adduction), extension, and extreme axial rotations. Common mechanism of injury : 1-Valgus force with foot planted 2- severe hyperextension injury of knee.

19. Cruciate Ligament Injury   Anterior cruciate ligaments: ACL attaches along anterior condylar area of the tibial plateau, to attach on medial side of the lateral femoral condyle. Most of its fibers are taught when knee approaches full extension . Functions :   1- Most fibers resist excessive anterior translation of the tibia or excessive posterior translation of the femur. 2- Limit full knee extension. 3- Resist extremes of varus, valgus and axial rotations. Mechanism of injury: 1- Hyperextension of knee. 2- Large valgus force with foot planted on ground. 3-Either of the above combined with large internal axial rotation torque e.g. the femur forcefully externally rotates over a fixed tibia.

20. Special Test: Anterior Drawer test:   Is based on the fact that ACL provide 85% of passive resistance to anterior translation of tibia, so the test is performed with pulling the tibia forward in knee flexed 90 degrees Anterior translation of 8 mm or 1/3 inch is indicative of a positive ACL injury. It may be masked by hamstring spasm (limiting anterior drawer of tibia).

21. Relation Between muscular contraction and ACL injury A contraction of quadriceps muscle extends the knee and slides the tibia anteriorly relative to the femur thus increase the tension in most fibers of the ACL. While contraction of the hamstring muscle, in contrast, causes a posterior translation of the tibia that slackens most fibers of the ACL. Thus in rehabilitation following injuries over strengthening of hamstrings is an essential component

22. Posterior Cruciate Ligament PCL attaches from the posterior intercondylar area of tibia to the lateral side of the femoral medial condyle. Become taught in extreme flexion, pulled taught by hamstring contraction and subsequent posterior slide of tibia. 1- Most fibers resist excessive posterior translation of the tibia or excessive anterior translation of the femur. 2- Most fibers taught in full knee flexion. 3- Some fibers are taught at extremes of varus, valgus and axial rotations Mechanisms of injury of PCL:  1-Hypeflexion of knee 2- Large valgus or varus force with foot planted . 3- Any of the above, combined with large axial rotation.

23. Posterior drawer test: Pushing tibia posteriorly with knee flexed 90 degree. Normally the PCL provide 95% degrees of passive resistance to posterior translation of tibia. Relation between hamstrings and PCL: Contraction of hamstrings muscles flexes the knee and slides the tibia posteriorly relative to the femur thus stressing the posterior cruciate ligaments. A contraction of quadriceps muscle extends the knee and slides the tibia anteriorly relative to the femur thus decreases the tension in most fibers of the PCL. Thus in rehabilitation following injuries over strengthening of hamstrings is an essential component

24. Patellofemoral Disorder  The patellofemoral joint is the interface between the articular side of the patella and the intercondylar groove on the femur. Painful Patellofemoral Joint: Patellofemoral joint pain syndrome is a common conditions, cases may be mild involving only a generalized aching about the anterior knee, or they may be severe and involve recurrent dislocation or sublaxation of the patella from the intercondylar groove. Overtime, some of them develop degenerative changes in the joint surfaces ( chondromalacia patellae).

25. Chondromalaciapatellae is charecterized by: 1- Excessive cartilage degeneration on the posterior side of the patella. 2-Those with this condition often experience retro-patellar pain and crepitus , especially while squatting or climbing steep stairs or after sitting a prolonged period. 3-The cartilage becomes soft, pitted, and fragmented. Note the irregular surfaces and marked degeneration on the cartilage of the femur and patella

26. C. Quadriceps Weakness (Extensor lag): Inability to fully extend knee in open kinematic in the last 15 to 20, Although the knee can be fully extended passively; commonly seen in persons with moderate weakness in the quadriceps. Biomechanical causes includes: 1- In moderate weakness as the knee approaches terminal extension, the maximal internal torque potential of the quadriceps is least while the opposing external (flexor) torque is greatest. 2- Swelling or effusion of the knee increases the likelihood of an extensor lag. Swelling increases intra articular pressure, which ca physically impede full knee extension, by reflexively inhibit the neural activation of the quadriceps muscle.

27. D. Patellectomy :   It is a condition of removal of the patella. In this case the patellar tendon lies closer to the center of the tibiofemoral joint than in a normal knee joint so the quadriceps muscle will act with a shorter lever arm, leading to increasing in the force requirements for the muscle. The quadriceps muscle has to develop more tension (about 30%) than is normally required. So in cases of patellectomy , the patient must be exercised to increase the strength of the quadriceps muscle by about 30% than normal (especially before operation).

28. Reference Curwin S (2011). Joint structure and function.  Levangie P.K., & Norkin C.C.(Eds.),  Joint Structure and Function: A Comprehensive Analysis, 5e . McGraw Hill. https://fadavispt.mhmedical.com/Content.aspx?bookid=1862&sectionid=136083890 Brown, L. P., & Yavorsky , P. (1987). Locomotor biomechanics and pathomechanics : a review.  The Journal of orthopaedic and sports physical therapy ,  9 (1), 3–10. https://doi.org/10.2519/jospt.1987.9.1.3