Acetabular dysplasia and hip osteoarthritis in Britain and Japan

Objective. Geographic differences in the prevalence of hip osteoarthritis ( OA) have been ascribed to differences in the frequency of acetabular dyspla sia among different ethnic groups. However, there are few data on the shape of the acetabulum in various populations around the world. We examined thi s issue in samples of pelvic radiographs from Britain and Japan. Methods. Measurements were made on the pelvic radiographs of 1303 men and 1 95 women, aged 60-75 yr, who attended for i.v. urography in two British cen tres. These were compared with 99 men and 99 women aged 60-79 yr who were i ncluded in a population-based study in a rural community in Japan, and who agreed to undergo standardized pelvic radiography. Acetabular dysplasia was assessed by morphometric measurement of the centre-edge (CE) angle and ace tabular depth. Results. The mean CE angle among men was 36 degrees (95% CI 35-37 degrees) in Britain and 31 degrees (95% CI 29-32 degrees) in Japan; that in women wa s 37 degrees (95% CI 36-38 degrees) in Britain and 31 degrees (95% CI 29-33 degrees) in Japan. The mean values of acetabular depth were also significa ntly (P < 0.001) lower in Japan than in Britain. However, the prevalence of hip OA was lower in Japan (0% in men, 2% in women) than in Britain (11% in men, 4.8% in women). In a random effects model, there were negative relati onships between measures of acetabular dysplasia and minimum joint space am ong individuals. Conclusions. We conclude that there are marked differences in pelvic morpho metry between Britain and Japan. The acetabular dimensions of Japanese subj ects are considerably shallower than those of their British counterparts of similar age and sex. Nevertheless, hip OA is more frequent in Britain than in Japan. Further studies are required on the risk factors for hip OA in O riental populations, in order that the aetiology of this disorder can be be tter understood.