The extensor mechanism consists of a chain of anatomical structures including the quads muscle and kneecap that work together to straighten the knee.

rectus femoris part of quadriceps muscle

The rectus femoris muscle is one of the four part sof the quadriceps (quads) muscle and is a key part of the complex. The patella (kneecap) is embedded in its tendon.


extensor mechanism


The of muscle, bone and tendon complex reaches from the hip, through the femur and patella to the tibia. The four heads of the quads muscle are intimately involved with a network of fibrous tissue on the sides of the patella (retinaculum) and the whole works pretty much as a unit, and is called 'the extensor mechanism'.


Injury of the extensor mechanism

If any part of this extensor mechanism breaks, for example -

  • fractured patella
  • rupture of quads muscle or tendon
  • rupture of patellar tendon
  • avulsion or 'pulling off' of the quads tendon or patellar tendon from their attachment to the patella
  • fracture of tibial tubercle (where the patellar tendon attaches to the tibia)
  • avulsion or 'pulling off' of the patellar tendon from its attachment to the tibia

then the knee will not be able to fully actively extend.



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