Reliability and Stability of Three Common Classifications for Legg-Calve-Perthes Disease

Abstract

To predict the course of Legg-Calv,-Perthes disease (LCPD) and select between treatment options in the early stages, it is critical to have a reliable predictive classification. We examined the reliability and stability of three common classification systems for LCPD. We identified 69 patients with LCPD, who had hip radiographs taken more than twice after the initial presentation with at least a 3-month interval. The Herring lateral pillar, Catterall, and Salter-Thompson classifications were evaluated in terms of reliability and stability. The inter- and intrarater reliability of the classification systems was determined by three orthopaedic surgeons using intraclass correlation coefficients (ICCs). To evaluate the stability of the classification systems, the percentage agreement and ICCs among the initial rating, rating when entering fragmentation, and final rating were used. The interrater reliability was highest in Herring lateral pillar classification (ICC, 0.885) followed by the Catterall and Salter-Thompson classifications (ICC, 0.802 and 0.702, respectively). The percentage agreement and ICC between the initial and final rating were, respectively, 55% and 0.491 for the Herring classification and 48% and 0.378 for the Catterall classification. Our data show the highest reliability of the classification of Herring et al. However, more than 40% of the hip radiographs at the initial presentation, and in particular, most of Herring Group A patients, were upgraded. Therefore, for patients older than 8 years old and graded as Herring Group A initially, surgeons should keep the possibility of surgical treatment in mind. Level I, diagnostic study. See Guidelines for Authors for a complete description of levels of evidence.