1. ESS 303 – Biomechanics Knee Joint

4. 2 convex surfaces (femur) articulating with 2 concave surfaces (tibia) Poor bony stability Stability increased with cartilage and ligaments Up to 80% of knee stability comes from muscles

5. Knee Joint 2 semicircular menisci surround the medial and lateral rims of the condylar facets of the tibia increase depth of concavity stabilize femur medial meniscus is larger of the two and allows slight rotation and locking mechanisms of the knee joint Medial tibial condylar facet is 50% larger than the lateral and has 3 times the articular cartilage thickness

6. Knee Ligaments The medial collateral ligament (MCL) prevents the knee from buckling inwards The lateral collateral ligament (LCL) prevents the knee from buckling outwards The anterior cruciate ligament (ACL) prevents the tibia from sliding forwards under the femur The posterior cruciate ligament (PCL) prevents the tibia from sliding backwards under the femur

7. Anterior ViewPosterior View ACL PCL MCL LCL

8. Common Knee Injuries Popliteal tendonitis (downhill gate) Deep squat (weightlifting) Breaststroker’s knee (swimming) ACL injury (alpine skiing – “phantom foot fall”) PCL injury (clipping) Meniscus injuries (most common knee injury, may case locking, ) Hurdler’s position stretch (pry apart MCL)

9. Knee Ligaments

11. Knee Positions Knock-Knee Femoral Varus Genu Valgum Tibial Valgus

12. Knee Positions Bow Leg Femoral Valgus Genu Varum Tibial Varus

13. Knee Positions Genu Valgum

14. Knee Positions Genu Varum

15. Knee Positions Genu Recurvatum

16. Knee Positions - Surgical Correction

17. Movements and Major Muscles Flexion: gastrocnemius & Hamstrings (semitendinosus, semimembranosus & biceps femoris) Extension: Quadraceps (rectus femoris, vastus lateralis, vastus medialis & vastus intermedius) Medial rotation (about 20° when flexed 90°): Semitendinosus & semimembranosus Lateral rotation (about 30° when flexed 90°): biceps femoris  Medial and lateral rotation allow feet (weight bearing and non-weight bearing) to turn without tearing knee ligaments