Prognostic value of bone resorption pattern in the anterior portion of the femoral head in Legg–Calvé–Perthes disease

PURPOSE: To examine whether differences in bone resorption patterns in the anterior portion of the femoral head correlate with the prognosis of Legg–Calvé–Perthes disease. METHODS: Seventy-eight patients with unilateral Legg–Calvé–Perthes disease, who were diagnosed after 6.0 years of age, underwent the Salter innominate osteotomy from 1987 to 2013, and were followed up to skeletal maturity. The anterior bone resorption pattern of the femoral head was evaluated from a frog-leg lateral hip radiograph made in the middle of the fragmentation period, and classified into two types, an epiphysis-preserved type (P) and a physis-disrupted type (D). The correlation between the type of bone resorption and the Stulberg outcome was analyzed. RESULTS: The Stulberg outcomes were grade I for 9 patients, grade II for 31, grade III for 35, and grade IV for 3, with a mean follow-up period of 8.3 ± 2.7 years. Fifty-one patients demonstrated the type P hips and 27 did the type D hip. In a subset analysis of patients with the modified lateral pillar group-B hips in the younger group (6.0–8.9 years of age at diagnosis), the percentages of the favorable and unfavorable outcomes significantly differed between the two types (p = 0.013). Anteroposterior enlargement of the affected femoral head was significantly greater in the type D hips than the type P hips (p = 0.014). CONCLUSION: Unfavorable hip morphology at skeletal maturity can be predicted in patients with the lateral pillar group-B hips by focusing on bone resorption patterns of the anterior portion of the femoral head. LEVEL OF EVIDENCE: Level III, prognostic study.