Knee Structure and Function Notes

Structure and Function of the Knee Complex

Overview of the Knee Complex

  • Largest, most complex weight-bearing joint in the body.
  • Biaxial modified hinge joint: Allows movements in two planes.
  • Composed of:
    • Tibiofemoral joint
    • Patellofemoral joint
  • Serves as a link between the hips and feet.
  • Functions effectively in both open-chain and closed-chain activities.

Bony Structures of the Knee

  • Femur

    • Shaft travels inferiorly and slightly medially.
    • Forms an average angle of 170° to 175° with the tibia.

  • Distal Femur

    • Comprised of medial and lateral epicondyles, intercondylar groove, and adductor tubercle.

  • Proximal Tibia and Fibula

    • Tibial plateaus serve as articulation surfaces for femur.
    • Intercondylar eminence aids in stability and alignment.
    • The fibula provides attachment for muscles and ligaments but does not articulate with the femur.

  • Medial and Lateral Condyles

    • Medial condyle is longer than the lateral condyle.

Patella

  • Largest sesamoid bone in the body.
  • Embedded within the quadriceps tendon.
  • Covered by smooth hyaline cartilage on its posterior surface, subject to high compressive and friction forces.
  • Increases the efficiency of the quadriceps muscle by enhancing the internal moment arm.

Function of the Menisci

  • Menisci are semicircular fibrocartilage structures that:
    • Absorb shock and distribute compression loads during weight-bearing activities.
    • Provide joint surface congruency for better stability and support.
    • Guide motion and help to reduce joint friction.
    • Nourish articular cartilage and provide proprioceptive input through innervation.

Ligaments of the Knee

  • Medial Collateral Ligament (MCL):
    • Protects against valgus forces; blends with other tissues to enhance stability.
  • Lateral Collateral Ligament (LCL):
    • Protects against varus forces; more isolated than MCL.
  • Anterior Cruciate Ligament (ACL):
    • Prevents excessive anterior translation of the tibia.
  • Posterior Cruciate Ligament (PCL):
    • Prevents excessive posterior translation of the tibia.

Kinematics of the Knee

  • Open-Chain osteokinematics involves the tibia moving relative to a fixed femur, allowing flexion and extension mainly in the sagittal plane.
  • Closed-Chain allows the femur to move over the fixed tibia, contributing to complex knee motions.
  • Screw-Home Mechanism:
    • Refers to the tibia laterally rotating during terminal extension, locking the knee for stability.

Muscle Action and Influence

  • Knee Extensors (Quadriceps):
    • Major contributors to knee extension; the rectus femoris also flexes the hip.
    • Produce significant force, critical in activities such as jumping or standing up.
  • Knee Flexors (Hamstrings):
    • Comprising Semimembranosus, Semitendinosus, and Biceps Femoris; assist in knee flexion while interacting with hip motion.
  • Functional Impact of hip positioning affects knee function:
    • Flexion and extension can limit or amplify movements depending on muscle position.

Patellar Tracking and Functionality

  • Optimal patellar motion is crucial during knee function and affects overall joint mechanics.
  • Factors influencing patellar tracking include:
    • Tightness in the IT band or lateral patellar retinacular fibers.
    • Laxity in medial restraints or overall joint alignment.