Treatment of developmental dislocation of hip: does changing the hip abduction angle in the hip spica affect the rate of avascular necrosis of the femoral head?

Avascular necrosis (AVN) of the femoral head is a serious complication in the management of developmental dislocation of the hip. Increasing the abduction angle increases its stability but compromises the vascularity of the femoral head. From our database of 240 children treated for developmental dislocation of hip by the two senior authors between 1998 and 2008, we defined two groups of children who underwent closed or medial open reduction of the hip after a failed Pavlik treatment or if patients presented late. In group 1, the reduced hip was immobilized in around 90° flexion, 60° abduction, and 0-10° internal rotation. In group 2 the hip was immobilized in around 45° of hip abduction with flexion and internal rotation as before. The first and second authors independently analysed these two groups blinded to the hip abduction angle. Our hypothesis was that a reduction in the hip abduction angle would reduce the incidence of AVN in the second group without compromising the stability. All eligible children were included, and there were 42 children in group 1 and 44 children in group 2. An almost equal number of children underwent closed and medial open reduction in both the groups. The age at reduction was a mode of 6 months (range 6-13 months) and 7 months (range 7-12 months), respectively. The abduction angle in the first group had a mode of 60° (range 52-70°) and the second group had a mode of 45° (range 38-50°). Radiographic evidence of AVN as described by Salter and colleagues was seen in eight children (19%) in the first group and seven children (16%) in the second group (P=0.78). Redislocation occurred in one child in the second group and none in the first group. In summary, the results show a nonsignificant reduction in the incidence of AVN when the hip abduction angle was reduced with no significant increased risk of redislocation.