Soft-tissue interposition after closed reduction in developmental dysplasia of the hip. The long-term effect on acetabular development and avascular necrosis.

We reviewed 98 children (133 hips) with developmental dysplasia of the hip who underwent arthrography immediately after closed reduction by overhead traction. We followed the patients to skeletal maturity to investigate whether soft-tissue interposition influences acetabular development and avascular necrosis over the long term. The shape of the limbus and the thickness of the soft-tissue interposition at the acetabular floor, as shown on arthrograms at the time of reduction, were not directly related to the final radiological results or to the incidence of avascular necrosis. Even if marked soft-tissue interposition was found on the initial arthrogram, spontaneous disappearance was noted in 71% up to the age of five years. The final radiological results showed no difference between those in which the interposition disappeared and those with none at the time of closed reduction. However, the requirement for secondary surgery at the age of five years was significantly higher in those with more than 3.5 mm of soft-tissue interposition. In the no-disappearance group (group C) further operation was necessary in 100% and the results were significantly worse at maturity according to Severin's classification. We suggest that the indications for open reduction should not be based solely on the arthrographic findings at the time of closed reduction.