Isolated osteochondral fracture of the patella without patellar dislocation

Chondral fractures of the patella are associated with acute dislocation of the patella. Osteochondral fracture in patellar dislocation is located in the medial facet of the patella. This article presents a case of a 15-year-old female ballerina with isolated displaced osteochondral fracture of the patella without patellar dislocation. She had no history of trauma. A Merchant's view of both knees showed mild subluxation of the patella, a small fragment on the lateral aspect of the knee, and a small defect of the centromedial patella. Axial magnetic resonance imaging (MRI) revealed an osteochondral fragment measuring 13 mm medial to the patella. However, the medial patellofemoral ligament and medial retinaculum were intact. An effusion on the medial side of the patella consistent with hemarthrosis was observed. An absence of a contusion or bone bruise on the lateral femoral condyle was shown. The loose body was removed arthroscopically. Intraoperative findings included a 1.5×2 cm osteochondral fragment. It is unusual that the osteochondral patellar defect site in this patient was in the inferior and central areas of the patella. Patellar chondral fractures without dislocation or patella fracture are rare. Therefore, the possibility of a trivial trauma leading to an osteochondral fracture should be kept in mind in adolescent and young adults who present with knee pain and hemarthrosis.