Neonatal hip instability. Reason for failure of early abduction treatment.

A series of nine children with hip joint instability in 17 hips, diagnosed neonatally, is presented. Seven had bilateral idiopathic instability and two instability secondary to arthrogryposis, one of them bilateral. After reduction seven of the children (14 hips) were treated with abduction devices, which in all cases did not lead to stability in one or both hips. In these cases arthrography revealed that closed reduction was impossible due to narrowing of the joint capsule (hour-glass shape) and the interposition of a capsular fold including the acetabular labrum. The same types of changes were seen within 1 or 2 months after birth in three hips which had had no abduction treatment before arthrography. At open reduction of 11 hips it was found that the narrowing of the capsule was caused by the tendons of the iliopsoas and rectus femoris muscles. Excision of the capsular fold (labrum) was not necessary. The femoral head was deformed and anteverted. Failure of conservative treatment can be due either to incomplete reduction or to inadequate immobilization. Our analysis has shown that the most probable reason is incomplete reduction due to interposition. An obstacle to reduction should be suspected if abduction is restricted at birth, if primary reduction is difficult and the position difficult to maintain or if instability persists after 8 weeks of treatment. On the basis of our material the incidence of such an impediment to reduction was 0.08 per thousand births in the region studied during a 5-year period.