Surgical images: musculoskeletal acetabular cartilage delamination demonstrated by magnetic resonance arthrography: inverted "Oreo" cookie sign.

a 5-year history of persistent left hip pain, which had been constant in nature over the last several months with increased severity after high activity and sitting for long periods. The pain was always present in the groin area, and would occasionally radiate to the knee. There was no history of hip disorders or other joint problems. The patient had no other significant problems or complaints. On physical examination, the patient had a slightly antalgic gait, with no leg-length discrepancy. The range of motion for the left and right hips, respectively, were as follows: flexion 110° and 115°; abduction 40° and 40°; adduction 0° and 0°; internal rotation 0° and 10°; and external rotation 35° and 35°. The impingement test gave a positive result in the left hip (i.e., flexion, adduction and internal rotation reproducing knife-like pain in his groin). His motor power was normal, particularly about his hip girdle. Plain x-ray films included an anteroposterior (AP) view of the left hip and a cross-table lateral view, with slight internal rotation of the left hip. On the AP view (Fig. 1), there were no signs of acetabular dysplasia or evidence of arthritis. On the lateral view (Fig. 2), the femoral head–neck offset was measured at 0.095 (approximate normal measurement should be > 0.19). Magnetic resonance imaging (MRI) arthrography with gadolinium