Late presenting dislocation of sonographically stable hips.

We report on seven developmental hip dislocations in five babies (age 6-22 months) in whom ultrasound had demonstrated reduced and stable hips. Four hips in three babies had been diagnosed as having clinical instability (Barlow positive) at birth, which had stabilized by the time of the scan (16-45 days). Femoral head coverage ranged from 36 to 56%. One hip had minimal sonographic laxity on stress examination. Hips that are reduced and stable sonographically at 2-6 weeks of age can subsequently dislocate. Any child with instability at birth should be reviewed with a pelvic radiograph at 4-6 months, even if an ultrasound scan appears to be normal.