Most Japanese patients have secondary osteoarthritis, mainly due to developmental dislocation of the hip (DDH) or acetabular dysplasia (AD). However, the precise pathomechanism of AD remains unknown. The purpose of this study was to investigate the frequency of bilateral AD and determine the correlation of the severity of AD between the right and left hips.
A total of 206 patients with prearthritis or early-stage osteoarthritis caused by AD were examined radiographically, and their history of treatment for DDH during infancy was reviewed. There were 187 women and 19 men included in the study, and the mean age at examination was 37.6 years (range 20-49 years).
A total of 174 patients (84%) had bilateral AD. In all, 72 (35%) of the 206 patients had a history of treatment for DDH (DDH group), and the remaining 134 (65%) had no history of DDH (non-DDH group). Bilateral AD was observed in 55 patients (76%) in the DDH group and 119 patients (89%) in the non-DDH group; the difference was significant. The center-edge angle, acetabular head index, acetabular angle, and acetabular roof angle showed positive correlations between the right and left sides in the non-DDH group. There was no correlation of the acetabular roof angle between the two sides in the DDH group.
A high rate of bilateral AD and a positive correlation of the severity of AD between the right and left hips were observed, especially in patients with no history of DDH. Our data suggest that in many patients AD occurred as a result of bone malformation involving bilateral hip joints. More research from a genetic standpoint is needed to elucidate the pathomechanism of this disease.