Introduction: Evaluation of the hip joint space was performed in patients with Legg-Calve-Perthes disease in this study.

Materials and Methods: Seventy-eight patients (85 affected hips and 71 unaffected hips) with LCP disease were reviewed respectively to evaluate widening of the hip joint space, the extent of epiphyseal subchondral fracture, and metaphyseal changes. The mean age of the patients was 7.4 years (range, 3–13 years). There were 27 hips at the initial stage, 23 at the fragmentation stage, and 11 at the healing stage. The metaphyseal changes in MRI scans were classified as no change, marrow edema, false cyst, and true cyst. The false cyst was defined as a cyst located at the epiphysis, physis, and metaphysis. The true cyst was defined as a cyst located within the metaphysis.

Results:The widened medial joint space at the initial stage was filled with overgrown cartilage of the femoral head and acetabulum on Magnetic Resonance Imaging (MRI) and radiographs. At the fragmentation stage, there was both overgrown cartilage and markedly widened true medial joint space, which was filled with an amount of joint fluid and hypertrophied synovial tissue. Widening of the true medial joint space at the initial stage had no correlation with lateral subluxation, whereas there was a definite correlation at the fragmentation stage. In the healing stage, coxa magna contributed to lateral subluxation rather than the widening of the false medial joint space, because it had decreased or normalized because of ossification of this overgrown cartilage and normalization of the synovial hypertrophy. The overall proportion of agreement was conducted by two groups of observers according to different classification systems. The results for Catterall groups 2, 3, and 4 showed 70% agreement with the Salter-Thompson classification, 65% with the MRI classification, and 75% in the Catterall classification. The subchondral fracture line had a prognostic significance in 17 of 20 hips (85%). The MRI had a prognostic significance in 10 of 20 hips (50%). Among 85 hips, there were no changes in 32 hips, marrow edema in 13 hips, false cysts in 28 hips, and true cysts in 12 hips.

Discussion: The hips without metaphyseal change had less involvement of the epiphysis compared to the hips with the metaphyseal change. Metaphyseal cysts disappeared on radiographs and MRI scans during the healing or remodeling stage.