Anatomy

ANATOMY

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Joints

Tibiofemoral Joint

Type

  • Modified Hinge Joint; Largest Synovial Joint in Body

Congruency

  • Relatively Flat Tibial Plateau with Oval Shaped Femoral Condyles = incongruent joint; improved by wedge shaped menisci
  • Reinforced by capsule, intra- and extra-articular ligaments (collateral, cruciate) and muscles (quadriceps, hamstrings, calf, popliteus)

Degrees of Freedom

  • 2 + 1 (flexion/extension, internal/external rotation with some abd/adduction)

Ligamentous Support

  • Anterior Cruciate Ligament
    • Prevents anterior translation of the tibia on the femur
    • At least part of the ACL is always under tension
    • Provides stability through range
    • Provides proprioceptive feedback
  • Posterior Cruciate Ligament
    • Prevents posterior translation of the tibia on the femur
    • At least some part of PCL always under tension
    • Provides stability through range
    • Provides proprioceptive feedback
    • Not necessarily as vital as ACL (so can usually get back to sport without surgery to reconstruct) but still important
  • Medial Collateral Ligament
    • Helps to reinforce the joint medially
    • Primary restraint to abduction of the knee
    • Also acts to assist in limiting extension
  • Lateral Collateral Ligament
    • Helps to reinforce the joint laterally
    • Assists to limit adduction of the knee
    • Acts to assist in limiting extension
  • Menisci
    • Improve Tibiofemoral conguency
    • Facilitate movement of the knee joint
    • Act as shock absorbers
    • The medial meniscus has attachment to MCL, while the lateral meniscus has an attachment to popliteus
  • Posterolateral Corner
    • LCL, Popliteus, Popliteofibular ligament (PFL), biceps femoris form the “posterolateral corner”
    • These structures reinforce the posterior aspect of the knee and are important to stability, particularly in extension / varus

Superior Tibiofibular Joint

Type

  • Fibrous joint analgous to the Radioulnar joints in the upper limb
  • Works with the Inferior Tibiofibular Joint

Degrees of Freedom

  • One Degree of Freedom – Pronation and supination; but normally minimal movement

Patellofemoral Joint

Type

  • Formed by the posterior surface of the patella and the femoral trochlear groove
  • The patella is a sesamoid bone within the quadriceps tendon and acts as an anatomical pulley to reduce the amount of force required to extend the knee as it comes closer to full extension (with a decreasing lever arm)

Congruency

  • Degree of congruency is variable depending on one’s anatomy.
  • Stability is aided by the fit of the patella into the trochlear groove and by musculoligamentous structures such as the medial retinaculum (blending with the vastus medialis) and the lateral retinaculum (which acts as a buttress to prevent lateral excursion).

Degrees of Freedom

  • The patella slides down in the groove (relatively) as the knee is flexed
  • There is also medial / lateral glide and superior / inferior glide

Kinesiology

  • As the knee approaches full extension (about 30 degrees of flexion), the smaller lateral femoral condyle runs out of articular surface and the ACL becomes taut.
  • The medial femoral condyle continues to roll and slide pivoting about a fixed lateral femoral condyle, with the ACL as the axis for movement.
  • At full extension, the collateral ligaments are taut, the tibial spines are lodged in the intercondylar notch and the menisci are tightly interposed between the articular surfaces.
  • Extension is the close packed position of the knee.
  • UNLOCKING is active and requires the action of popliteus which rotates the femur laterally.
  • In closed kinetic chain movements:
    • During flexion, the femur rolls posteriorly and slides anteriorly
    • During extension, the femur rolls anteriorly and slides posteriorly