The other hip in unilateral hip dysplasia.

UNLABELLED: We reviewed transverse pelvic computed tomography scans of 197 consecutively referred adult patients with hip pain thought to be secondary to developmental dysplasia. A center-edge angle of 20 degrees or less was considered the upper normal value. Four groups were identified: 69 patients with apparently unilateral right developmental dysplasia (left hip center-edge angles greater than 20 degrees), 26 patients with apparently unilateral left developmental dysplasia (right hip center-edge angles greater than 20 degrees), 68 patients with bilateral developmental dysplasia, and 34 patients with bilateral borderline developmental dysplasia (bilateral center-edge angles less than or equal to 25 degrees). The pelvic computed tomography scans were compared with computed tomography scans of 41 control subjects with healthy hips. The joint anatomy of patients with developmental dysplasia differed from that of control subjects in almost all aspects. Acetabular anteversion was larger in control subjects compared with patients with developmental dysplasia. We found inverse relationships between femoral anteversion and the anterior acetabular sector angle and coronal and sagittal center-edge angles in dysplastic hips, and also between femoral neck-shaft angles and the anterior acetabular sector angle. There was an inverse relationship between reduced anterior support developmental dysplasia in which plain radiographs suggested unilateral dysplastic abnormality only, computed tomography scans revealed both hips to be abnormal. The data suggest that patients referred with seemingly unilateral developmental dysplasia also are at risk of having contralateral dysplastic malformation. LEVEL OF EVIDENCE: Diagnostic study, Level II (development of diagnostic criteria on consecutive patients [with universally applied reference "gold" standard]). See the Guidelines for Authors for a complete description of levels of evidence.