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Knee Extensor Mechanism

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Basic illustration of the extensor mechanism of the knee[1]
  • Extensor Mechanism
  • Quadriceps Femoris formed by the confluence of 4 muscles into the quadriceps tendon:
  • Quadriceps Tendon
    • Insertion on the proximal pole of the patella as well as on the dorsal, lateral, and medial surfaces
    • Composed of 3 planes: superficial (rectus femoris), middle (vastus medialis and lateralis), deep (vastus intermedius)
  • Patellar Tendon
    • Distal continuation of quadriceps tendon when it extends past the inferior patellar pole
    • Inserts onto tibial tubercle
    • Dimensions
      • Thickness 4-7 mm (proximal), 5-6 mm (distal)[2]
      • Length 4-6 cm
      • Width 25-40 mm
    • Does not have a well-developed paratenon
    • Hoffa fat pad deep to tendon has close relationship to tendon
    • "Patellar Ligament"
      • Misnomer because the patella is a sesamoid bone
      • Embryologically the quadriceps tendon attaches to the tibia
      • Mesenchymal condensation develops and becomes the patella


  • Action is to transmit forces from the quadriceps to the proximal tibia
  • Efficiency is increased 1.5x because of the presence of the patella[3]

Vascular Supply


Clinical Significance

See Also


  1. Image courtesy of drerikhohmann.com, "Knee Extensor Mechanism"
  2. el-Khoury GY, Wira RL, Berbaum KS, Pope TL Jr, Monu JU. MR imaging of patellar tendinitis. Radiology 1992;184(3): 849–854
  3. Rauh M, Parker R. Patellar and quadriceps tendinopathies and ruptures. In: DeLee JC, ed. DeLee and Drez’s Orthopaedic Sports Medicine. Philadelphia, PA: Saunders; 2009:1513–1577
Created by:
John Kiel on 10 October 2020 18:48:30
Last edited:
21 April 2024 21:49:00