Neutral pelvic positioning during recording of anteroposterior pelvic radiographs has been recommended for precise interpretation of acetabular deformities. Because the effect of pelvic positioning is controversial in the literature, we asked whether the weightbearing position would alter radiographic interpretations. We obtained sets of supine and weightbearing anteroposterior pelvic radiographs of 31 patients with developmental dysplasia of the hip and measured pelvic tilt, acetabular version, center edge angle, acetabular index, joint space width and femoral head translation. For both genders the pelvis extended when patients were repositioned from supine to weightbearing but extension was more pronounced in women compared with men. The number of patients with apparent acetabular retroversion was reduced from 11 supine to four when weightbearing. The center edge angle, acetabular index, joint space width and femoral head translation were similar in both views. We recommend weightbearing anteroposterior pelvic radiographs be obtained to assess DDH given the differences in pelvic flexion-extension and interpretations of acetabular version.
Level of evidence: Level III, diagnostic study. See the Guidelines for Authors for a complete description of levels of evidence.