Factors leading to hip subluxation and dislocation in femoral lengthening of unilateral congenital short femur

Congenital short femur is a rare and complex deformity. For it to be treate d in the most accurate way, we must know of every possible complication. Th e purpose of this study was to determine the factors leading to hip subluxa tion or dislocation in patients with an unilateral congenital short femur w ho underwent a femoral lengthening procedure. Forty-foul patients with cong enital unilateral short femora types I, ii, and IIIA were seen between 1981 and 1993 at Alfred I. duPont Hospital for Children. Seventeen patients had type I, 9 patients had type II, and 18 patients had type IIIA. Twenty pati ents underwent simultaneous lengthening of the femur and tibia, and 24 pati ents had primary lengthening of the femur. Eleven patients had an epiphysio desis of the contralateral femur for I residual leg length discrepancies of <6 cm, We observed that in patients with type IIIA, the acetabular dysplas ia is severe, as well as the coxa vara deformity. and is associated with pr ogressive subluxation and dislocation of the hip with lengthening. We belie ve that the combined abnormality of corn vara and bow of the femoral shaft contributes to hip subluxation and dislocation in congenital short femur in association with an acetabular dysplasia prior to the lengthening. We reco mmend correction of the varus bow of the femur allii the neck-shaft angle t o 120 degrees and the acetabular index to < 25 degrees prior to lengthening of type IIIA femora.