The extensor mechanism is the complete musculotendinous-bony chain transmitting quadriceps force to the tibia. Each component (quadriceps tendon, patella, patellar tendon) is a potential failure site. The patella increases the mechanical advantage of the quadriceps by 50% by moving the tendon away from the knee axis. Complete disruption at any level produces the same clinical presentation — inability to perform a straight leg raise.
Knee extension — the most important lower limb function for ambulation, stair climbing, and rising from a chair
Extensor mechanism disruption level is identified by: (1) suprapatellar gap — quadriceps tendon rupture, (2) high-riding patella on lateral X-ray — patellar tendon rupture, (3) comminuted patella — patellar fracture. Treatment principles are the same: restore length and continuity of the mechanism with non-absorbable suture or wire, then rehabilitate with progressive extension exercises.
Quadriceps tendon, patellar fracture, or patellar tendon rupture producing inability to straight leg raise — surgical repair of the disrupted segment restores extension.
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