The importance of surgeons' experience on intraobserver and interobserver reliability of classifications used for Perthes disease.

The objective of this study was to evaluate the percentage agreement and intraobserver and interobserver reliability for the Catterall, Salter-Thompson, Herring, and Stulberg classification systems, with special reference to the experience of surgeons. AP and frog-leg radiographs of 10 patients were evaluated by 18 reviewers with three levels of experience on two occasions. Each patient had three sets of radiographs of different stages of disease (initial stage, fragmentation phase, and healed phase). The interobserver percentage agreement rates were 28% for residents, 42% for senior surgeons, and 51% for pediatric orthopaedists for the Catterall classification in the initial stage; 63%, 46%, and 68% for the Salter-Thompson classification; 44%, 44%, and 61% for the Herring classification; and 34%, 37%, and 43% for the Stulberg classification at skeletal maturity. The Catterall, Herring, and Salter-Thompson classifications have a learning curve, and pediatric orthopaedists have better intra- and interobserver reliability. The Stulberg classification system when used at skeletal maturity consistently gave the best results for intraobserver and interobserver reliability for residents, senior surgeons, and pediatric orthopaedists. These results suggest that although the reliability of these classification systems improves with the experience of the observer, inter- and intraobserver error is generally high even among experienced pediatric orthopaedists.