Racial and geographic factors in the incidence of Legg-Calvé-Perthes' disease: a systematic review.

Legg-Calvé-Perthes' disease (Perthes' disease) is a childhood osteonecrosis of the hip for which the disease determinants are poorly understood. In this review, the authors identify studies of Perthes' disease incidence published up to December 2010 and make denominator populations comparable in order to allow meaningful between-study evaluation. Incidence rates and confidence intervals were determined, and, where appropriate, denominator populations were obtained from national statistical offices. Poisson regression was used to determine the influence of race and geography. The review included 21 studies that described 27 populations in 16 countries, with 124 million person-years of observation. The annual incidence among children under age 15 years ranged from 0.2 per 100,000 to 19.1 per 100,000. Race was a key determinant, with East Asians being least affected and whites most affected, though data were insufficient to consider incidence among blacks (for South Asians vs. East Asians, incidence rate ratio = 2.9, 95% confidence interval (CI): 2.4, 3.5; for whites vs. East Asians, incidence rate ratio = 8.8, 95% CI: 8.2, 9.6). Latitude was a strong predictor of disease, even after adjustment for race. Each 10° increase in latitude was associated with an incidence increase of 1.44 (95% CI: 1.30, 1.58) times. While much of the international variation appears to be a function of race, latitude demonstrates a strong association. This observation may offer new epidemiologic insights into the determinants of Perthes' disease.