Periosteal avulsion of the posterolateral corner of the knee in an adolescent: an unreported case.

Isolated injuries of the posterolateral corner of the knee are uncommon injuries in adults and are relatively unheard of in the pediatric population. This article reports a case of a 13-year-old boy who sustained an external rotation injury to his proximal tibia on a slightly flexed knee while playing football. Radiographs showed an avulsed fragment from the lateral femoral condyle. A magnetic resonance image was read as an avulsion of the femoral insertion of the lateral collateral ligament with associated bone bruise of the lateral femoral condyle. At operation, the fragment consisted of the femoral insertion of the popliteus tendon and the lateral collateral ligament, which was anatomically reduced and internally fixed with a screw and soft tissue washer. Six weeks postoperatively, the patient had full range of motion. To our knowledge, this injury has not been reported in the pediatric population.