Stability of the hip joint after reduction of late-diagnosed congenital dislocation of the hip.

Nine children with late-diagnosed congenital dislocation of the hip underwent ultrasonography for determination of the influence of hip flexion on hip stability after reduction. No medication was used, and the investigation was performed in existing abduction splints during active movements of the leg. Redislocation of the joint was related to the minimal degree of flexion (120, 110, 100, or 90 degrees) permitted by the splint. All hips redislocated when flexion was less than 100 degrees. Five joints need 100 degrees and two 110 degrees of flexion for prevention of redislocation, and two hips required as much as 120 degrees.