Subsidiary lateral femoral condyle in arthrogryposis multiplex congenita

A previously undescribed anomaly of the distal femur occurred in a 3-month-old child with arthrogryposis multiplex congenita. There was a large boss of bone superior and posterior to the true lateral femoral condyle with which the lateral tibial femoral condyle articulated. To obtain full extension of the knee, it was necessary to perform a full posterior release and to replace the tibial condyle distally onto the true lateral condyle. The etiology of the anomaly remains conjectural, but the lesion should be sought for in patients with resistant flexion contracture requiring surgical release.