Both the quadriceps and the patella tendon are part of the knee extensor mechanism. The quadriceps tendon connects the four front muscles of the thigh to the top of the kneecap (patella). The patella tendon connects the bottom of the kneecap to the shin bone (tibia). Together, they help extend the knee to a straight position.

In most cases, there is some degeneration (aging) of the tendon that weakens it and allows it to tear. Sometimes tears occur during falls, sometimes they occur during athletic activities. The history of the injury, level of difficulty walking, and the physical exam are important information. X-rays often show the kneecap in an unusual location (too high or too low). MRIs may confirm these tears in certain cases.

Surgical repair is usually recommended. This cannot be done arthroscopically, as it requires exposure of the tendon to repair it to the kneecap.