Valgus slipped capital femoral epiphysis without posterior displacement: two case reports.

Valgus slipped capital femoral epiphysis is a rare entity; approximately, 26 cases in 31 hips have been reported in the orthopedic literature since 1926. It has been argued that epiphyseal displacement occurs only in a posterior or posteromedial direction, and that the radiographic appearance of true valgus or lateral slippage is an optical illusion owing to the rotation of the femur. We present the cases of two sisters with bilateral lateral slipped capital femoral epiphysis without a posterior component of displacement. In these cases, the radiographs suggested that the direction of displacement was in the lateral plane and was confirmed with computerized tomography and three-dimensional reconstructions. Analysis demonstrated the absence of posterior slippage of the proximal femoral epiphysis. The slippage was treated with percutaneous screw placement. In cases in which the direction of the slip may be in question, advanced imaging techniques may be useful for precise determination of the screw placement. This may assist in the preoperative planning, and reduce the risk of inappropriate screw placement.