Comparison of pelvic radiographs in weightbearing and supine positions.

UNLABELLED: We asked whether radiographic angles and signs of hip osteoarthrosis differ between radiographs of the pelvis taken in standing and supine positions. We retrospectively reviewed the radiographs of 61 patients (72 hips) with developmental dislocation of the hip. The minimum followup after closed reduction was 15 years (mean, 44 years; range, 15-64 years). We used pelvic radiographs in supine and standing positions taken at the same time and determined the following parameters: minimal joint space width, acetabular roof obliquity (AC angle), depth of the acetabulum (ACM angle), and center-edge angle. Osteoarthrosis was assessed according to Kellgren and Lawrence. Two independent observers measured all radiographs manually with a goniometer. AC angle, center-edge angle, and minimum joint space width differed between the radiographs taken in supine and standing positions at followup, whereas osteoarthrosis grading and the ACM angle did not. The AC angle depended on patient position and predicted development of osteoarthrosis. The minimum joint space width was influenced by the radiographic position with greater values in the supine position. ACM angle and the osteoarthrosis grade according to Kellgren and Lawrence were unaffected by the patient's position.

LEVEL OF EVIDENCE: Level II, prognostic study. See the Guidelines for Authors for a complete description of levels of evidence.