Occult Incarcerated Osteochondral Fracture of the Medial Patellar Facet Following Acute Lateral Patellar Dislocation in an Adolescent: A Case Report.

Acute lateral patellar dislocation is a common injury in adolescents and is most frequently associated with rupture of the medial patellofemoral ligament (MPFL). Concomitant osteochondral fractures may remain occult or be misinterpreted on initial imaging, resulting in delayed diagnosis and potentially compromising long-term joint function. We present a rare case of an incarcerated osteochondral fracture of the medial patellar facet that was initially misinterpreted as arising from the medial femoral condyle following acute lateral patellar dislocation. A previously healthy 15-year-old boy presented to King Hussein Medical City Emergency Department approximately one week after his injury following an acute traumatic lateral patellar dislocation sustained while playing football. Clinical examination demonstrated persistent lateral patellar subluxation and knee instability. Initial plain radiographs and computed tomography demonstrated a displaced osteochondral fragment and persistent lateral patellar subluxation; however, the fragment was initially interpreted as arising from the medial femoral condyle. Although advanced imaging was performed, the anatomical origin of the incarcerated osteochondral fragment was not correctly recognized preoperatively. Surgical exploration unexpectedly revealed an incarcerated osteochondral fracture of the medial patellar facet rather than an isolated ligamentous injury. The fragment was anatomically reduced and stabilized using three headless compression screws supplemented with a suture anchor to repair the MPFL, successfully restoring the patellar articular surface and patellar stability. A structured postoperative rehabilitation program resulted in fracture healing, progressive functional recovery, and return to pre-injury activities without recurrent patellar instability. This case highlights the diagnostic challenge of occult osteochondral injuries associated with acute lateral patellar dislocation in adolescents. Persistent patellar maltracking or subluxation following reduction should raise suspicion for an incarcerated osteochondral fragment, even when conventional imaging appears consistent with an isolated MPFL injury. Careful preoperative evaluation combined with meticulous intraoperative assessment is essential for identifying repairable osteochondral lesions. Early anatomical reduction and stable fixation can restore joint congruity, preserve native articular cartilage, and achieve excellent functional outcomes while potentially reducing the risk of recurrent instability and post-traumatic osteoarthritis.