Knee

• Tibiofemoral Joint:

  • Located between the proximal tibia and distal femur
  • Double condyloid joint with 3 degrees of osteokinematic motion:
  • Flexion/Extension (0 - 140°)
  • Medial/Lateral rotation (0 - 35°)
  • Abduction/Adduction (8 - 13°)
• Femur:

  • Large medial and lateral condyles
  • Condyles are convex, with the medial condyle being larger and having a greater radius of curvature than the lateral condyle
• Tibia:

  • Relatively flat, slightly convex tibial plateaus
  • Menisci improve joint congruence
  • Medial tibial plateau is larger relative to lateral tibial plateau
  • Articular cartilage is thicker on the lateral tibial plateau relative to the medial
• Joint Arthrokinematics:

  • Movement described relative to fixed segment
  • Open (loose) packed position at 25 - 30°
  • Closed packed position at 0°
• Screw Home (Locking) Mechanism:

  • Obligatory lateral rotation of tibia with knee extension
  • Shorter lateral tibial plateau and lateral femoral condyle complete rolling motion before longer medial structures
• Medial Collateral Ligament:

  • Superficial and deep portions
  • Primary restraint to valgus and lateral tibial rotation
  • Becomes lax with knee flexion
• Lateral Collateral Ligament:

  • Separate from joint capsule
  • Primary restraint to varus stress
  • Lax with knee flexion
• Anterior Cruciate Ligament:

  • Anteromedial and posterolateral bands
  • Primary restraint to anterior translation of tibia on femur
• Posterior Cruciate Ligament:

  • Posteromedial bundle and anterolateral bundle
  • Primary restraint to posterior tibial translation on femur
• Menisci:

  • Fibrocartilaginous disks
  • Medial meniscus is C-shaped, while the lateral meniscus is 4/5 of a circle
  • Thicker along the periphery
  • Outer 1/3 has neurovascular supply
• Knee Joint Muscles:

  • Extensors: Quadriceps, Articularis Genu
  • Flexors: Hamstrings, Sartorius, Gracilis, Popliteus, Gastrocnemius, Plantaris
• Forces:

  • Genu valgum (>185°) leads to greater lateral compartment loading
  • Genu varum (<175°) leads to greater medial compartment loading
• Patellofemoral Joint Forces:

  • Can be influenced by knee angle and quadriceps tension
  • Medial aspect has greater stress
  • Can reach 5-6x body weight with running and jumping
• Dynamic Valgus:

  • Consistent mechanism of injury. * Hip internal rotation coupled with knee external rotation
  • Increases patellofemoral contact forces
• Joint Forces and Exercise:

  • Weight-bearing activities have minimal anterior shear and peak posterior shear at 80-105°
  • Non-weight-bearing activities have anterior shear at 40-0° and posterior shear at 60-100°
• Anterior Cruciate Ligament:

  • Posterior shear force at the knee during weight-bearing activities
  • Increased patellofemoral joint stress with increased knee flexion angles
• The knee joint is the largest synovial joint in the body
• The knee joint has two compartments, medial (inner) and lateral (outer)
• It consists of three bones: femur, tibia, and patella.
• The menisci are fibrocartilage structures that act as shock absorbers between the femur and tibia.
• Muscles generate force through contraction and contribute to stability and motion.
• Medial condyle extends further distally (relative)
• Initial flexion (0-25°) is produced by rolling of femur (fixed tibia)
• Patellofemoral Joint Motion

  Flexion/Extension (superior/inferior glide)

  Medial/Lateral

  ◦ Tilt

  ◦Rotation (follows tibia)

  ◦ Shift
• The patella acts as anatomical pulley

  ◦ Deflects action line away from joint center

  ◦ Increasing angle of pull

  ◦ lengthens the moment arm. * Increases ability of muscle to generate torque