The epidemiology and etiology of Perthes disease.

The incidence of Perthes disease varies markedly both between countries and within countries down to a local level. The disease is more common in white than in Asian or black African children. The disease is associated with deprivation; with a steep disease gradient across social class groups. This epidemiology alongside the lack of concordance in twins suggests a strong environmental etiology, with little evidence to suggest a genetic predisposition. Children are frequently short, with a growth pattern described as "rostral-sparing". A propensity to associated congenital anomalies suggests an intrauterine cause.