Methods of measuring in Legg-Calvé-Perthes disease with special regard to the prognosis.

For scientific, statistical comparisons of results of treatment of Legg-Calvé-Perthes disease (LCPD), a standard classification of the stage of the disease, and a precise definition of the method of evaluation of the results are necessary. A precise measurement of the sphericity of the head, and measuring of the epiphyseal quotient, joint surface quotient and radius quotient are recommended. By this very strict separation, one obtains a good spread on the groups for statistical tests. Ideally, the measuring ought to be made at the age of 16 or later, when growth has stopped and quotients will no longer change. For the purpose of treatment and advising patients of their prognosis a simple and easily performed method of evaluation should be used, for instance, measuring the sphericity of the head and the radius quotient (RQ). The RQ can be easily determined at the same time as the countour of the circle of the head is defined. The RQ is sufficiently strict, can be measured after the closure of the epiphyseal line, and also gives a good indication of protrusion of the head beyond the acetabular margin. Studies comparing measurements on plane roentgenograms with arthrographic findings in the cartilagenous surface are needed.