the biomechanical basis for rupture of extensor mechanism of knee joints at different sites

Rupture of the extensor mechanism of knee joints is rare in patients without any systemic disease. many reports have described tendons getting ruptured at various sites of the extensor mechanism. we report a case of patellar tendon avulsion from the tibial tuberosity on the right side and quadriceps tendon avulsion from the patella on the left side sustained in one accident. a 54 years old man presented with the above non-identical bilateral extensor mechanism rupture who had no pre-existing systematic diseases and was not on any steroid treatment. tendon ruptures were always related to systemic degenerative/inflammatory conditions or usage of steroids. however, the reason for the rupture of different parts of the extensor mechanism after minor trauma in case of tendinopathy or after a significant trauma in a normal patient is not well explained. we believe that the degree of knee flexion at the time of injury plays an important role in the site of rupture of the extensor mechanism.