Introduction: It has been proposed that the presence of the capital femoral ossific nucleus confers protection against ischaemic injury or avascular necrosis (at the time of reduction of a congenitally dislocated hip). The current literature is contradictory.

Materials & Methods: A prospective study was undertaken of the clinical and radiological outcomes following closed or open reduction. 50 hips were included in the study. These cases had either presented late or had failed conservative treatment. In 28 hips treatment was intentionally delayed until the appearance of the ossific nucleus (but not beyond 13 months) and in 22 the ossific nucleus was present at clinical presentation. 6 hips reached the age of 13 months without an ossific nucleus appearing and progressed to treatment. The significant avascular necrosis rate (> grade 1) was 7% for closed reduction and 14% for open. However, the amended rate if hips were excluded that had failed Pavlik harness treatment was 0.0% and 9% respectively (4% overall). Further surgical procedures were necessary in 57% of hips undergoing closed reduction and 41% after open, which compares favourably with other series.

Discussion: It is concluded that the presence of the ossific nucleus is an important factor in the prevention of AVN, particularly after late closed reduction. Intentional delay in the timing of surgery does not condemn a hip to open surgery but there is a comparable rate of secondary procedures becoming necessary particularly after closed reduction. The delayed strategy to await the appearance of the ossific nucleus for previously untreated dislocation allows a simple treatment algorithm to be employed which produces good clinical and radiological outcomes. The use of the Pavlik harness has been abandoned in cases of irreducible dislocation of the hip.