Patellar stress fracture is a rare condition. It has been described in young athletes, patients with cerebral palsy, and following patellar resurfacing surgery.

In the athletic group, onset of pain is gradual and due to chronic overload. This is important to diagnose and treat (primarily through load management), as these will heal with appropriate rest, but could progress to frank fracture if unrecognised.

The radiographic appearance of stress fracture is marked by sclerotic margins, which reflect attempted reparation and osteoblastic activity. Conversely, acute traumatic patellar fractures are marked by lucent fracture margins. It is important to distinguish these entities from bipartite patella.

This case is unusual in that the fracture line is in the coronal plane. Patellar stress fractures are usually transverse, and occasionally longitudinal.