Anatomy of Knee Joint in a Nutshell

Anatomy of Knee Joint

• Has fibrous capsule
  • Different form hip joint

• • • In hip, capsule surrounded whole joint
    • In the knee, capsule is open anteriorly where patellar ligament is in the midline and not invested by the capsule

• • • Off to the sides of the patella = retinacula of the knee joint
      1. Medial / lateral retinaculum
      2. These come from the tendinous fibers of vastus muscles.

• • On posterior aspect, is reinforced by bands of connective tissue (493)

• • • Oblique popliteal ligament:
      1. Is an extension of the tendon of Semimembranosus as it attaches the tibia
      2. Some fibers course across the posterior surface of the capsule to reinforce it by forming this ligament
    • Arcuate popliteal ligament:
      1. Is associated with popliteus muscle (has origin on lateral chondyle and attaches to the area superior to soleal line)
      2. This muscle enters the fibrous capsule of the knee joint (not within synovial membrane though)
      3. As it comes out of capsule, it has fibers that reinforce the capsule = arcuate popliteal ligament.

• Knee joint has additional ligaments
  • 2 extracapsular ligaments = collateral ligaments that lie outside capsule
    • lateral collateral = fibular collateral ligament

1. • 1. 1. is a cord outside the capsule
        2. strengthens external surface
   • Medial collateral = tibial collateral ligament
     • From femur to tibia
     • Is more of a broad sheet

• • When flex knee, these are loose. When straight these collateral ligaments stabilize the knee joint

• 2 intracapsular ligaments = between capsule and synovial membrane
  • Posterior cruciate ligament (PCL)
    • From tibia (between articular surfaces)
    • Strongest of intercapsular ligaments
    • Most tension during full knee flexion

• • Anterior curciate ligament (ACL)
    • Attaches medial side of lateral epichondyle
    • Forms a cross with PCL = “cruciate” shape
    • Most tension during full knee extension

• Menisci: clinically important

• • 2 crescent shaped disks of articular cartilage: medial / lateral
  • Are attached to the tibia to facilitate movement of the joint / absorb shock
  • Each has two portions
    • Lateral aspect: has more vasculature, damage more apt to heal
    • Inner medial aspect: no vasculature, relies on synovial fluid.

1. 1. 1. 1. Projects toward the articular surface
         2. Damage may be permanent
         3. Bits of meniscus may wander the joint as “joint mice”.

1. 1. 1. 1. 1. will cause pain if lodged between the bones of the knee joint / between condyles.
            2. patient will show “locking” to avoid pain

• (posterior) Meniscofemoral ligament
  • On posterior aspect
  • extends from lateral meniscus and blends with posterior cruciate ligament
  • regulates movement of meniscus.
• Lateral aspect of each meniscus is different.
  • Lateral meniscus:

1. 1. • On lateral side, the tendon of popliteus is between fibular collateral ligament and meniscus
      • Thus lateral meniscus has greater mobility than medial meniscus.

1. • Medial meniscus:

1. 1. • Medial collateral ligament is fused with lateral margin of the medial meniscus.
      • Thus, movement of medial meniscus is restricted by attachment to medial collateral (tibial collateral) ligament.

• • • Trauma to medial collateral ligament usually also involves medial meniscus.

• Clinical:
  • Most trauma to knee joint is caused by a lateral blow at knee level when foot is planted when knee is slightly flexed.
  • Unhappy Triad:

1. 1. • Stress is put on medial side of the knee which potentially tears three related structures
      • Medial collateral ligament, medial meniscus, ACL

1. • Anterior cruciate ligament is responsible for preventing the tibia from sliding anteriorly and separating from femur.

1. 1. • As the knee flexes the ACL together with PCL keep the bone in normal relationship
      • if ACL damaged, the femur will slide posterior and tibia goes anteriorly.

1. • The PCL is damaged when person falls on tibial tuberosity, it drives tibia posteriorly, thus femor goes anteriorly.
   • Drawer test: patient has knee flexed, fix thigh with one hand, grab tibia

1. 1. • If it slides anteriorly = ACL damage
      • If move posteriorly = PCL damage.

1. • McMurry’s Test:

1. 1. • Test damage to menisci. Patient sits with knee flexed. Rotate the tibia to force it medially / laterally.
      • If experience pain on medial rotation, have medial meniscus damage

• • • If have pain on lateral rotation, have lateral meniscus damage.

• • • Can have healthy knee joint with loss of both ligaments, key is then development of muscles around the joint- especially Vastus muscles.

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