Biomechanics of Knee Joint

Knee Joint

• Tibiofemoral Joint Function
  • Flexion/Extension:
    • Axis of flexion and extension passes through the femoral epicondyles
    • ACL causes femoral condyle to glide posteriorly during flexion and anteriorly during extension
    • PCL causes femoral condyle to glide anteriorly during flexion and posteriorly during extension
• Rotation
  • Occurs about a longitudinal axis through the medial tibial intercondylar tubercle
  • Limited rotation possible when knee is in full extension due to taut ligaments and menisci
  • Increased rotation possible when knee is flexed to 90°, with a total medial/lateral rotation of approximately 35°
  • Medial tibial condyle and intercondylar tubercle act as pivot points during rotation
• Patellofemoral Joint Motion
  • 0-20° of flexion:
    • Tibia internally rotates, decreasing lateral pull on the patella
    • Patella moves into intercondylar groove and follows it until 90° of knee flexion
    • Contact area is mainly at the inferior pole of the patella
  • 20-90° of flexion:
    • Patella moves in intercondylar groove
    • Contact areas are along lateral and medial patellar facets with lateral and medial condyles
  • 90-135° of flexion:
    • Patella moves laterally and tilts medially into intercondylar groove
    • Odd facet contacts medial femoral condyle at about 135° of knee flexion

Load Transmission through the Knee Joint

• Trabecular Pattern
  • Distal end of femur: contains vertical and horizontal trabeculae
  • Proximal end of tibia: contains similar sets of trabeculae
• Load Transmission
  • Force applied to the superior aspect of the tibia is resolved into a vertical component (v) and a transverse component (t)
  • Transverse component (t) tends to tilt the joint medially and exacerbate physiological valgus
  • Medial ligaments prevent dislocation

Meniscus Injuries

• Twisting Movement of the Knee
  • Mechanism of injury: twisting of the body around a fixed flexed leg
  • Consequences:
    • Longitudinal splitting of the meniscus
    • Complete detachment of the meniscus from the capsule
    • Complex tear of the meniscus
  • Knee "locks" in a position of flexion
• Violent Extension of the Knee
  • Mechanism of injury: violent extension of the knee (e.g. kicking a football)
  • Menisci fail to follow the movements of the femoral condyles on the tibial condyles
  • Consequences:
    • Transverse tears or detachment of the anterior horn

Ligamentous Injury

• Anterior Cruciate Ligament (ACL) Injury
  • Common in sports, approximately 70% of ACL injuries are non-contact
  • Mechanism of injury: femur rotates on the planted leg with the knee close to full extension
  • Sudden changes in direction combined with acceleration or deceleration of the body
• Posterior Cruciate Ligament (PCL) Injury
  • Most commonly result from sport participation or motor vehicle accidents
  • Mechanism of injury: hyperflexion of the knee with the foot plantarflexed
  • Impact with the dashboard during motor vehicle accidents can result in combined ligamentous damage