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Geographical distribution of the associated factors of osteonecrosis of the femoral head, using the designated intractable disease database in Japan.

OBJECTIVES
Osteonecrosis of the femoral head (ONFH) is a designated intractable disease (DID) in Japan. The Ministry of Health, Labour, and Welfare launched an online registry system for DIDs. We aimed to investigate the epidemiological characteristics of patients with ONFH using the DID database.


METHODS
Data of patients with ONFH registered in the DID database between January 2004 and December 2013 were extracted. The incidence of new cases and distributions of sex, age, and associated risk factors were investigated. The prevalence of the two categories, 'steroid-associated' and 'alcohol-associated' risk factors, was estimated for each prefecture.


RESULTS
New 15,049 cases of ONFH were investigated. The mean registration rate-corrected annual ONFH incidence per 100,000 individuals was 1.77. The male-to-female ratio was 1.33. Age distribution peaked in the 40s and 50s for male and 60s for female. The prevalence of steroid-associated ONFH was lower in males (28.6%) than in females (49.8%), while that of alcohol-associated ONFH was higher in males (47.2%) than in females (9.3%). No clear region was identified for the steroids. The incidence of alcohol-associated ONFH was significantly higher in Tokyo and Okinawa, regardless of sex.


CONCLUSIONS
Alcohol-associated ONFH incidence varies geographically across Japan, suggesting that it has regional characteristics.