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KNEE

KNEE. Tibiofemoral Joint. Modified hinge joint. Articulating surfaces: Femoral condyles: Convex and asymmetric. Medial condyle is larger than the lateral. Condyles are separated anteriorly by patellar groove. Condyles are separated posteriorly by intercondylar fossa.

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KNEE

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  1. KNEE

  2. Tibiofemoral Joint • Modified hinge joint. • Articulating surfaces: Femoral condyles: Convex and asymmetric. Medial condyle is larger than the lateral. Condyles are separated anteriorly by patellar groove. Condyles are separated posteriorly by intercondylar fossa.

  3. Tibiofemoral Joint • Articulating surfaces: Tibial plateaus: Concave and asymmetric. Articular surface of medial plateau is 50% larger than that of lateral. Separated by intercondylar tubercles.

  4. Menisci • Wedge-shaped fibrocartilage discs. • Ends of menisci = horns: Attached to intercondylar tubercles. • Coronary ligaments: Attach menisci to rims of plateaus. • Anterior transverse ligament: Joins menisci and allows them to move together.

  5. Menisci • Medial meniscus: Larger of the two. More securely attached. Also attached to medial collateral ligament and to semimembranosus muscle. More often injured than lateral.

  6. Menisci • Lateral meniscus: Attached to posterior cruciate ligament: Via meniscofemoral ligament. Attached to popliteus muscle.

  7. Menisci • Functions: Enhance stability of knee: Deepen articular surfaces. Distribute weight. Reduce friction between articular surfaces.

  8. Menisci • Movement: Medial meniscus moves posteriorly during flexion: Due to tension in semimembranosus muscle. Medial meniscus drawn forward during extension: Due to tension in anterior capsular fibers.

  9. Menisci • Movement: Lateral meniscus moves posteriorly during flexion: Drawn by tension in popliteal expansion. Distorts more than medial meniscus.

  10. Joint Capsule • Large and lax. • Deficient on lateral condyle: For passage of popliteal tendon. • Anterior wall replaced by quadriceps tendon. • Excludes cruciate ligaments. • Commonly communicates with synovial bursae.

  11. Bursae • Suprapatellar: Upward expansion of synovial cavity between femur and quadriceps muscle and tendon. Proximally receives insertion of articularis genus muscle.

  12. Bursae • Prepatellar: Lies between superficial surface of patella and skin. • Deep Infrapatellar: Lies between patellar ligament and tibia.

  13. Bursae • Subpopliteal. • Gastrocnemius: Under medial head of gastrocnemius.

  14. Bursae • Anserine bursa: Between pes anserinus and tibial collateral ligament. Note: pes anserinus = combined tendons of semitendinosus, gracilis, and sartorius.

  15. Ligaments • Collaterals: Medial (tibial): Attachments: Medial femoral condyle. Proximal tibia. Partly continuous with adductor magnus tendon. Attached to medial meniscus. Distally separated from tibia by genicular vessels and nerves.

  16. Ligaments • Collaterals: Lateral (fibular): Splits tendon of biceps femoris muscle. Separated from lateral meniscus by popliteal tendon.

  17. Ligaments • Anterior cruciate: Weakest of cruciates. Slack during flexion and taut during extension. Prevents backward sliding of femur on tibia. Prevents hyperextension of knee.

  18. Ligaments • Posterior cruciate: Taut during flexion and slack during extension. Prevents forward sliding of femur on tibia. Prevents hyperflexion of knee.

  19. Movements • Flexion: First part (0 to 25 degrees): Posterior rolling and spinning. Anterior sliding of femoral condyles on tibial plateaus. • Extension: First part: Femoral condyles roll anteriorly and slide posteriorly. Followed by rolling and spinning of condyles.

  20. Movements • Lateral-medial rotation of tibia: At 90 degrees of knee flexion: Up to 40 degrees of lateral rotation. Up to 30 degrees of medial rotation. Greater than 90 degrees of flexion: Medial and lateral rotation ROM decreases.

  21. Locking at Full Extension • During final few degrees of extension: Femur rotates medially on tibia. (Note that tibia would also rotate laterally on femur.) Knee is brought into close-packed position: Tibial tubercles are lodged in intercondylar notch. Menisci are tightly interposed between tibial and femoral condyles. = Locked or screw-home mechanism. • Popliteus laterally rotates femur for unlocking at beginning of knee flexion.

  22. Axes • Mechanical axis: From head of femur to head of talus. Almost equivalent to anatomic axis of tibia. • Anatomic axis: Extends along femoral shaft.

  23. Axes • Physiologic valgus: Normal angle at knee where femoral and tibial axes meet: 170 – 175 degrees.

  24. Axes • Genu valgum: Lateral deviation of tibia. Less than 170 degrees. Results in “knock knees.”

  25. Axes • Genu varum: Medial deviation of tibia. Greater than 170 degrees. Results in “bow legs.”

  26. Patellofemoral Joint • During knee flexion/extension: Central ridge of patella slides along central groove of femur.

  27. Patellofemoral Joint • During flexion: Tibia moves posteriorly. Ligamentum patellae pulls patella distally and posteriorly: Causes patella to remain firmly in apposition to femur.

  28. Patellofemoral Joint • During extension: Patella is pulled proximally by quadriceps. Vastus lateralis tends to pull patella laterally. Vastus medialis oblique counteracts vastus lateralis.

  29. Patellofemoral Joint • Q-angle: Formed by vector of quadriceps: From ASIS to middle of patella. And vector of pull of ligamentum patellae: From tibial tubercle to middle of patella. 15 degrees.

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