Perthes' disease after "irritable hip": delayed bone age shows the hip is a "marked man".

We report 13 children, aged 4 through 8 years, who were seen with a prolonged or recurrent irritable hip syndrome. Only those with > 2 years' delay in their bone age eventually declared themselves to have been in the early phase of Perthes' disease at initial examination when the original hip radiographs had been normal. A plain wrist radiograph was found to be a useful screening tool to differentiate those who should have early repeat investigation such as radiographs, or preferably a magnetic resonance image scan if available, to detect the disease in its initial phase. This facilitated early regular imaging to assess femoral head shape and so permitted early treatment before deformity had occurred in those with whole-head involvement.