Revised arthrographic index of deformity for Perthes' disease.

We report a new arthrographic index to quantitate the loss of sphericity of the femoral head during early Perthes' disease. The technique has been applied to 272 arthrograms of 131 normal and 141 affected hips. It measures marginal or segmental collapse as well as central collapse of the epiphysis, thus providing a more accurate assessment of deformity in 57.4% of anteroposterior and 46.8% of lateral radiographs as compared with the previous standard measurement (caput index). The measurement principle applies equally to other recent radiological developments such as magnetic resonance imaging.