Limited knee extension--a reliable indicator of a successful closed reduction of developmental dysplasia of hip.

A clinical observation of 49 hips in children who had closed reduction and application of hip spica for developmental dysplasia of hip (DDH) was undertaken in our department. A clinical sign of "Limited Extension at ipsilateral knee" was observed after successful closed reduction of the hip. This sign was absent if the hip was not reduced. This sign was due to hamstring tightness after successful closed reduction. We suggest that the presence of this sign is a reliable indicator of successful closed reduction and also an indicator of the vulnerability of the proximal femoral epiphysis to increased pressures during positions of immobilization.