The extensor mechanism is the anatomical structure that allows you to straighten your knee.  It is composed of the quadriceps, the patella, and the patellar tendon.  If any of the structures in this chain are disrupted, the function of the knee and lower extremity is extremely compromised.

If this disruption occurs around a total knee arthroplasty, special techniques may need to be employed to return function to the knee.  This may include replacement of the entire extensor mechanism with cadaveric tissue or a synthetic mesh.  

The recovery following the extensor mechanism reconstruction is prolonged and often requires a period of maintaining the knee in an extended position (straight leg) with a brace, while the reconstruction heals.