Relationship between lateral subluxation and widening of medial joint space in Legg-Calve-Perthes disease

Fifty-five patients (61 affected hips and 49 unaffected hips) with Perthes disease were reviewed to evaluate the relationship between widening of medi al joint space and lateral subluxation of the femoral head in radiographs. The components of the medial joint space were evaluated by using T-1, T-2, proton, and Gd-enhanced T1WI magnetic resonance images (MRI). The widened m edial joint space in radiographs was filled with overgrown cartilage at the initial stage (27 hips) in MRI, with both overgrown cartilage and widened true medial joint space at the fragmentation stage (23 hips) and widened tr ue medial joint space at the healing stage (11 hips). Between affected hips and unaffected hips, the mean difference of medial joint space in radiogra phs between hips at the initial stage and at the fragmentation stage was 2 and 4.5 mm, respectively; the mean difference in percentage of lack of cove rage of the femoral head between hips at the initial stage and at the fragm entation stage was 3 and 15%, respectively. During the healing stage, widen ing of the medial joint space decreased or normalized because of ossificati on of overgrown cartilage despite the existence of lateral subluxation beca use of coxa magna. We concluded that widening of the medial joint space may be used as an index of lateral subluxation at only the fragmentation stage in Perthes disease.