A Unifying Radiographic Description of Legg-Calvé-Perthes Disease at Skeletal Maturity: The Head, Acetabulum, Trochanter Classification.

BACKGROUND We revaluated the radiographic results of a 2004 landmark, multicenter prospective study of patients with Legg-Calvé-Perthes disease (LCP). In the current study, we developed a new classification to evaluate the femoral head, acetabulum, and greater trochanter in the hips of patients with LCP, to address what we found to be deficiencies in the Stulberg rating system, which is based mainly on femoral head shape. METHODS We digitized and analyzed approximately 5,000 radiographs and related data sheets of 337 patients (345 hips) with LCP from the 2004 study. We found many unexpected abnormalities, including serious lesions of the femoral head, that had not been noted in that study. To record our findings in the femoral head, acetabulum, and greater trochanter, we developed a classification system that we termed the HAT (Head, Acetabulum, Trochanter) classification, which assigns the femoral head 1 to 5 points, the acetabulum 1 point if dysplastic, and the greater trochanter 1 point if elevated to or above the femoral head. The sum is the HAT score, which we compared with the Stulberg score, other predictive factors, and the Nonarthritic Hip Score (NAHS) from two 20-year follow-up studies of a number of patients from the 2004 study. RESULTS The intraclass correlation coefficient (ICC) of the HAT score was 0.93 (95% confidence interval [CI]: 0.90 to 0.95), and the total HAT score correlated strongly with the NAHS. Forty-nine percent of all hips had acetabular dysplasia, which correlated with a worse NAHS. A HAT of ≤3 was considered a good result. The odds of a patient developing acetabular dysplasia at skeletal maturity were lower after surgical treatment than after nonoperative treatment. In addition, surgically treated patients had better HAT scores than nonoperatively treated patients, especially if their skeletal age was ≥6 years at LCP onset. Better outcomes were also associated with a favorable lateral pillar classification, a younger skeletal at onset, and male sex. CONCLUSIONS The HAT classification is reproducible and allows a more comprehensive analysis of the radiographic outcomes of LCP. The system is flexible and would allow for different measures of its 3 components in future studies. LEVEL OF EVIDENCE Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.