Epidemiological study of osteonecrosis of the femoral head using the national registry of designated intractable diseases in Japan

Objectives We aimed to investigate the epidemiological characteristics of osteonecrosis of the femoral head (ONFH) using the designated intractable diseases (DID) database in Japan. Methods Data on patients who had received public subsidies for medical costs due to ONFH from 2012 to 2013 were extracted from the DID database. The incidence and prevalence of ONFH, distribution of gender, age, and the prevalence of associated risk factors were assessed. These epidemiological characteristics were compared with those of another nationwide ONFH survey conducted during a similar period. Results Data on 3264 newly diagnosed patients (incident cases) and 20,042 patients registered until 2013 (prevalent cases) were evaluated. The corrected annual incidence and prevalence of ONFH per 100,000 were 3.0 and 18.2-19.2, respectively. The ratio of males to females was 1.4 in 2012 and 1.2 in 2013, respectively. Peak distribution was observed at ages 40s and 60s in males and females, respectively. The prevalence of the risk factors were steroid-associated: 39%, alcohol-associated: 30%, both: 4%, and none: 27%. Conclusions The DID database data showed a similar distribution of gender and age to that in other nationwide surveys but lower incidence and prevalence of ONFH. Sampling bias may affect the epidemiological characteristics of ONFH.