Sonographic detection of unilateral hip dislocation in a spica cast after closed reduction for developmental dysplasia of the hip.

OBJECTIVES

To determine the value of sonography for evaluating unilateral hip dislocation in a spica cast after closed reduction for developmental dysplasia of the hip.

METHODS

Seventy-three cases of unilateral hip dislocation were detected by sonography after closed reduction and monitored through the perineal opening of the cast during follow-up. The transinguinal approach was used first to determine the position of the femoral head. Then a sonogram of the bilateral hips was obtained by transverse scanning on the lower margin of the pubic symphysis. To determine the status of the affected femoral head, a bilateral comparison of the femoral head positions was made by measuring the horizontal distance from the medial rim of each femoral head to a center line through the pubic symphysis.

RESULTS

In all 73 cases, the femoral head position after reduction could be identified by sonography. With the transinguinal approach, the reduction was successful in 69 cases and unsuccessful in 4. On the sonograms of the bilateral hips, the dislocated femoral heads were repositioned in the acetabular fossa in the successful cases and redislocated posterolaterally in the unsuccessful cases. Among the successful cases, the position differences were less than 2 mm in 61, 3 to 4 mm in 7, and 5 mm in 1. In the unsuccessful cases, the positions of the bilateral hips were asymmetric; the differences were indecipherable after an unsuccessful first reduction but were 3 to 5 mm after a successful second reduction. During follow-up, the differences were never greater than 2 mm in the cases with initial differences of less than 2 mm and gradually decreased to less than 2 mm in those with initial differences of greater than 2 mm.

CONCLUSIONS

Sonography can be considered as the first imaging tool for evaluating the effect of closed reduction for developmental dysplasia of the hip.