Hip osteoarthritis (OA) is a common disabling disease, which has a much higher prevalence in whites than in Asians. The reasons for this ethnic difference in prevalence are unknown. Hip OA is often thought to be secondary to morphologic abnormalities. This study was undertaken to examine whether particular abnormalities predisposing to hip OA occur more frequently in whites and whether these differences in hip shape account for differences in the prevalence of OA.
A morphometric study was performed on 400 hips of 200 female participants without OA from 2 studies, the Beijing OA Study and the Study of Osteoporotic Fractures from the US. We focused on measures of hip dysplasia and impingement (lateral center-edge angle, impingement angle, acetabular slope, femoral head-to-femoral neck ratio, and the crossover sign) and compared data from the hips of Chinese and white women.
Compared with their Chinese counterparts, white women had a lower mean impingement angle (83.6° versus 87.0°; P=0.03) and were more likely to have center-edge angles suggestive of impingement (>35°; 11% of hips in Chinese versus 23% of hips in whites, P=0.008). In contrast, low center-edge angles suggesting dysplasia (<20°) were found more often in Chinese women (22% of hips in Chinese versus 7% of hips in whites, P=0.005).
In a study of elderly women without signs of OA, the morphometry of impingement and asphericity was more common in the hips of white women compared with Chinese women. Our findings suggest that whites may be at higher risk of hip OA than Chinese because of morphologic findings that predispose whites to femoroacetabular impingement.