Propagation of a patellar stress fracture in a basketball player.

Cyclic loading of cortical bone with repetitive, low-intensity loading can result in damage at its microstructural level. If this damage accumulates over time without appropriate repair, the strength of bone is reduced. Accumulation of fatigue damage may be manifest as stress fractures. As a link in the extensor mechanism of the leg, the patella is subject to complex loading, which varies with knee flexion and extension. Stress fractures of the patella originate on its anterior cortex and rarely propagate to completion.