Incidence of legg-calvé–perthes disease and slipped capital femoral epiphysis in Japan: insights from analysis of a large claims database

Abstract Background Legg-Calvé–Perthes disease (LCPD) and slipped capital femoral epiphysis (SCFE) are uncommon but clinically important pediatric hip disorders that may lead to long-term disability without timely diagnosis and treatment. However, relevant population-based epidemiological data for Japan are limited. This study aimed to estimate LCPD and SCFE incidence rates among Japanese children by using information from a large-scale health insurance claims database. Methods This retrospective cohort study used the Japan Medical Data Center claims database, which contains anonymized data from employer-sponsored health insurance plans in Japan. Children aged 2–14 years with sufficient follow-up were included in the incidence analyses during the study period (2017–2023). Annual cohorts were constructed from 2017 to 2021. New LCPD and SCFE cases were identified using the International Classification of Diseases, 10th revision, diagnostic and procedure codes, and incidence rates stratified by age and sex were calculated. Results A total of 2,116,499 children aged 2–14 years were included in the incidence analyses. Overall, 94 and 55 incident cases of LCPD and SCFE, respectively, were identified. The average annual incidence of LCPD in boys and girls aged 2–12 years was 2.75 and 0.51 per 100,000 person-years, respectively. The corresponding values for SCFE in the 7–14 years age group were 2.08 and 0.49 per 100,000 person-years. The incidence of LCPD and SCFE peaked at 3–6 and 11–12 years of age, respectively. Significant seasonal variation was observed in SCFE cases, with fewer diagnoses occurring in winter. Conclusions This study provides the first detailed population-based estimates of age-specific LCPD and SCFE incidence rates in Japanese children. Although both conditions are rare, the findings revealed distinct age- and sex-specific patterns and suggested that incidence has remained relatively stable compared with earlier Japanese reports. These epidemiological insights may help guide early detection efforts and inform healthcare planning for pediatric musculoskeletal disorders in Japan.