Knee Joint Biomechanics: A Comprehensive Guide

Posted on Nov 9, 2024 in Physical Education

Knee

Structure

The knee joint comprises the tibiofemoral (trochlear bicondylar) and patellofemoral articulations. Key components include the joint capsule, menisci, trabecular system, ligaments, and tendons.

Osteokinematics

Active Movements:

  • Flexion: 140° of the tibia on the femur
  • Extension: 180° of the tibia on the femur
  • Medial Rotation of the tibia on the femur
  • Lateral Rotation of the tibia on the femur

Close Packed Positions:

  • Patellofemoral: 30° to 60° flexion
  • Tibiofemoral: Full extension (180°) or -5° hyperextension

Loose Packed Positions:

  • Patellofemoral: Hyperextension or -5° flexion
  • Tibiofemoral: 10° to 20° flexion

Arthrokinematics

Movement Components:

Extension (Foot Off Ground):

  • Patella slides superiorly over the femur
  • Tibia glides anteriorly on the femur
  • Medial condyle glides posteroanteriorly; lateral condyle glides anteroposteriorly

Flexion (Foot Off Ground):

  • Patella slides inferiorly over the femur
  • Tibia glides posteriorly on the femur
  • Anterior tibia tilts on the femur (up to approximately 100° of flexion)
  • Medial condyle glides anteroposteriorly; lateral condyle glides posteroanteriorly

Joint Play Movements:

Patellofemoral:

  • Equilibration in the transverse axis
  • Equilibration in the longitudinal axis
  • Medial and lateral glides

Tibiofemoral:

  • Distraction
  • Medial and lateral tilt

Tibiofibular:

  • Anterior/lateral glide
  • Posterior/medial glide
  • Superior/inferior glide

Knee Auto-Rotation

Open Chain: Difference in length of the tibial plateau contact area.

Closed Chain: Unequal development of the condylar contour, glenoid shape, and lateral ligament orientation.

Muscle Action in Auto-Rotation:

Open Chain:

  • Knee Flexion (Internal Rotation): Semitendinosus, semimembranosus, gracilis, popliteus
  • Knee Extension (External Rotation): Tensor fascia lata

Closed Chain:

  • Knee Flexion (External Rotation): Popliteus

Ligament Function

Ligament Function in Open Chain Movement

  • Knee Extension: ACL resists external rotation.
  • Knee Flexion: PCL resists internal rotation.

Ligament Function in Closed Chain Movement

  • Knee Extension: PCL facilitates internal rotation of the femur.
  • Knee Flexion: ACL facilitates external rotation of the femur.

Patellofemoral Mechanics

Factors Influencing Patellofemoral Stability

  • Q-angle
  • Lateral trochlear facet
  • Quadriceps mechanism
  • Vastus medialis oblique (VMO)

Patellar Mechanical Function

  • Increases quadriceps lever arm
  • Provides functional stability under load
  • Creates an articular surface for the trochlea
  • Transmits quadriceps force during flexion
  • Protects the trochlea and condyles

Stability in Valgus and Varus Movements

  • Valgus Stability: Posterior medial capsule
  • Varus Stability: Posterior lateral capsule

Stability in Rotational Movements

  • Internal Rotation Stability: Anterolateral capsule and posterior medial capsule
  • External Rotation Stability: Posterior lateral capsule

Stability in Extension Movements

Posterior medial and lateral capsules contribute to stability during extension. The posterior capsule’s contribution is three times greater than the medial and lateral capsules.

Meniscal Mechanics

Factors Affecting Meniscal Capture

Open Chain:

  • Extension: Tension in the meniscopatellar ligament (medial and lateral menisci) and meniscofemoral ligament (lateral meniscus)
  • Flexion: Popliteus contraction (lateral meniscus) and semimembranosus contraction (medial meniscus)

Closed Chain:

  • Flexion and Extension: Movement of the femoral condyles

Factors Influencing Meniscal Movement

Closed Chain:

  • Active Factor: Tension in meniscopatellar fibers
  • Passive Factor: Displacement of the condyles

Open Chain:

  • Active Factor: Transverse and coronary ligaments

Meniscal Mechanical Function

  • Increases congruence between femoral and tibial articular surfaces
  • Participates in weight-bearing
  • Aids in joint lubrication
  • Resists valgus and varus movements (0° to 20° flexion) and rotations
  • Lateral meniscus resists internal rotation (closed chain)
  • Medial meniscus resists external rotation (closed chain)

Knee Ligament System

  • Patellar ligament
  • Posterior ligaments (oblique popliteal, arcuate popliteal)
  • Medial collateral ligament (MCL)
  • Lateral collateral ligament (LCL)
  • Anterior cruciate ligament (ACL)
  • Posterior cruciate ligament (PCL)

Mechanical Function of Collateral Ligaments

  • MCL: Resists valgus stress, external rotation, and excessive extension and flexion
  • LCL: Resists varus stress, external rotation, and excessive extension
  • Both MCL and LCL: Lock the knee in full extension (closed chain)

Mechanical Function of Cruciate Ligaments

  • Guide femoral and tibial movement
  • Primary stabilizers against anteroposterior movement (30° to 90° flexion)
  • Secondary stabilizers against varus and valgus stress
  • Resist axial rotation in flexion and extension
  • Resist flexion and extension movement