Avulsion fractures of the patella.

Forty-seven skeletally immature patients with marginal fractures of the patella were evaluated. We showed that avulsion fractures may affect the superior, inferior, and medial margins of the patella, separating through the subchondral bone along the biomechanically susceptible margin of progressive chondroosseous transformation and expansion of the ossification center. In children, the small size of the osseous fragment may belie the actual size of the more peripheral, radiolucent cartilaginous component. Treatment may be either conservative or operative, depending on the extent of separation of the fragments and the functional capacity of the patellar/quadriceps mechanism.