Intra and interobserver concordance between the different classifications used in Legg-Calvé-Perthes disease

The aim of this study was to determine the intra and interobserver concordance rates of the Waldenström, Catterall and Herring classifications for Legg-Calvé-Perthes disease.

One hundred radiographs of the pelvis in anteroposterior and Lauenstein views, from patients with this disease, were selected. The radiographs were classified by four physicians with different levels of experience who had previously been given guidance regarding the classifications used, in order to minimize any bias of interpretation. The radiographs were examined by the same observers at two different times in order to evaluate the intra and interobserver concordance. Reproducibility was assessed using the kappa index.

The concordance analysis was stratified into levels (poor, slight, fair, moderate, good and excellent). The intraobserver analysis showed, for the Waldenström classification, moderate concordance for three examiners and fair for one; for Herring, excellent for one examiner and good for three; and for Catterall, good for all the examiners. The interobserver analysis showed: for the three classification systems, no situations of excellent concordance; for Waldenström, four situations of fair concordance, one moderate and one slight; for Herring, four situations of moderate concordance, one good and one fair; and for Catterall, four situations of moderate concordance and two fair.

The classifications studied are the ones most used for guiding the treatment for Legg-Calvé-Perthes disease, but the degree of intra and interobserver concordance is far from ideal. Complementary staging systems need to be taken into consideration, so that there can be greater certainty regarding the treatment.