Open‐configuration MRI study of femoro‐acetabular impingement

Femoro‐acetabular impingement has been proposed as a causative factor of primary hip osteoarthritis. However, primary osteoarthritis of the hip is infrequent in Japan and other Asian countries, even though the hips of Asians frequently sustain impingement, since the Asian lifestyle commonly requires a larger range of hip motion than the Western lifestyle. Therefore, using open‐configuration MRI, we investigated whether impingement actually occurs during some traditional Japanese hip positions. The hips of 5 healthy Japanese females were examined in 5 sitting postures: 1) sitting straight; 2) bowing while sitting straight; 3) sitting cross‐legged; 4) W‐sitting; and 5) squatting. The impingement point was detected by multiple plane reconstructed (MPR) views along with the acetabular rim depicted circumferentially. Impingement was considered to have occurred when, on MRI, the anterior femoral head‐neck junction approached the acetabular rim and the femoral head was seen to float from the bottom of the acetabulum with the acetabular rim acting as a fulcrum. Impingement was observed in all volunteers in the W‐sitting position, and in 2 of 5 volunteers during squatting. These findings show that impingement occurs frequently during daily Japanese activities. Thus, depending on race, femoro‐acetabular impingement might not always cause primary osteoarthritis of the hip. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 25:1582–1588, 2007