A large laterally displaced osteochondral fragment from dislocated patella: Case report and possible mechanism

Dislocation of the patella is not a common disorder of the knee joint and is seen most frequently in the adolescent population. Osteochondral fractures account for approximately 5-74% of all acute patellar dislocations and are easy to overlook. The mechanism of injury and presentations of fractured fragments were seldom well describe in published studies. The case reported here is that of a 17-year-old baseball player who suffered an acute patellar dislocation with a large osteochondral fragment fracture, where the fragment presented over the lateral supracondylar aspect of the distal femur. Open reduction and fixation with Kirschner wires gave a good result. Osteochondral fracture of patella is usually regarded as a dislocation phenomenon. However, we review and discuss here three injury mechanisms, and suggest the possible mechanisms by which patellar relocation could have caused our patient's injury and the rare occurrence of a laterally displaced osteochondral fragment over the distal femur.