Knee Anatomy

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MUSCLES

Pes Anserinus

  • includes sartorius, gracilis & semitendinosis (Say Grace before Tea)

  • sartorius – very broad insertion, forming a sheath over gracilis & semiT

  • Gracilis – smaller & anterior to semiT

  • Semitendinosis – enveloping muscle belly extending more distally

  • Functions – flexor of knee & internal rotator of tibia

Iliotibial Tract

  • inserts into Gerdy's tubercle on the tibia & extends to form the lateral patellar retinaculum

  • also attaches to the lateral femoral condyle forming a static lateral restraint

  • Function: since it crosses the centre of rotation of the knee moving from flexion to extension it acts as a flexor in flexion & an extensor in extension

Biceps Femoris

  • multiple insertions

  • 3 layers:

    1. superficial layer – superficial to LCL

    2. middle layer – surrounds LCL

    3. deep layer – attaches to head of fibula & Gerdy's tubercle on tibia

  • Function – flex knee & externally rotate tibia

Popliteus

  • forms floor of popliteal fossa

  • muscle attached to posterior tibia – tendon passes intraarticularly deep to femoral attachment of LCL to attach to femur

  • Functions 

    • flex & internally rotate tibia when leg is free OR externally rotate femur on tibia when tibia is fixed.

    • dynamic reinforcement of PCL, preventing post. displacement of tibia on femur

Semimembranosis

  • 5 distal attachments:

    1. Oblique Popliteal ligament – broad oblique expansion; tightens posterior capsule

    2. Posteromedial capsule – semiM fuses with posterior capsule to form the Posterior Oblique Ligament (static stabiliser & resists anteromedial rotation)

    3. Deep Head – anterior expansion deep to MCL

    4. Direct Head – direct attachment to post medial tibial condyle; palpable with knee flexed

    5. Anterior Expansion – superficial fascial expansion coursing over fascia in leg.

KNEE STABILISERS (Anatomical)

Medial (Warren & Marshall):

  • Layer 1:

    • crural fascia – envelopes sartorius & gastrocnemius; joins periosteum of tibia with sartorius

  • Layer 2:

    • superficial MCL parallel fibres

    • Posterior oblique ligament

    • semimembranosis

  • Layer 3:

    • Deep MCL

    • True capsule – comprising the meniscofemoral & meniscotibial portions = Coronary ligament

Lateral:

  • Layer 1:

    • iliotibial tract

    • superficial portion of biceps

  • Layer 2:

    • patello-femoral ligament

    • retinaculum

  • Layer 3:

    • LCL

    • Arcuate ligament

    • joint capsule

Posterolateral Complex:

  1. Arcuate Ligament

    • Y shaped condensation of fibers that courses from the fibular head, over the popliteus

    • When fabella is large, there is no arcuate ligament & fabellofibular ligament is robust

  2. Lateral Collat ligament (LCL)

  3. Popliteus tendon

  4. Popliteofibular ligament

    • fibers originate from the popliteal tendon and insert onto the fibula
    • deep to the arcuate ligament and its fibers orientation are opposite from the arcuate ligament
  5. Reinforced by biceps, popliteus, & lateral head of gastrocnemius

Arcuate Complex:

  1. LCL
  2. Arcuate ligament
  3. Popliteus
  4. (Gastrocnemius)
  5. (Biceps)

Posterior Capsule:

  • formed mainly by the Oblique Popliteal Ligament

Also divided into Primary & Secondary Stabilisers – depending on the displacement

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