Extensor Mechanism Injury in Multiple Ligament Injured Knee

Patellar tendon and quadriceps tendon ruptures in the multiple ligament injured knee are an uncommon but important injury to diagnose. Acute fixation is generally accepted to be vital to improved clinical outcomes. The most common mechanism of injury is eccentric contraction of the quadriceps muscle against the weight of the body. This stress causes pathological tendons to rupture atraumatically, and as such many patients presenting with this injury have an underlying systemic illness which predisposes the tendon to rupture. Patients less than 40 are more likely to suffer a patellar tendon rupture, while patients older than 40 are more likely to rupture the quadriceps tendon. Classic physical exam findings include acute onset of knee pain, inability to extend the knee, and either a suprapatellar gap for quadriceps tendon rupture or infrapatellar gap for patellar tendon rupture. Diagnosis is aided by radiography as well as MRI which can diagnose associated intra-articular pathology. The anterior cruciate ligament is the most common ligamentous injury associated with patellar tendon ruptures.