Incidence and natural history of "head at risk" factors in Perthes' disease.

Twenty-eight cases of Perthes' disease were evaluated roentgenographically a minimum of 4 years after diagnosis (range, 4-17 years). The original roentgenograms were examined to see if a prognosis was possible of the final result on the basis of: (1) "head at risk" factors, or (2) Catterall's degree of epiphyseal involvement. Five "head at risk" factors more accurately predicted the course of Perthes' disease than Catterall's degree of epiphyseal involvement. The latter may change as the disease progresses. There is a definite decreasing incidence of a good radiological result with an increasing number of risk factors. The 5 risk factors are: Gage's sign; lateral subluxation; calcification lateral to the epiphysis; diffuse metaphyseal reaction and a transverse epiphyseal plate. The ability to predict the probable course of the disease and the final result should allow early institution of a more rational treatment program.