The incidence of and risk factors for developing atypical femoral fractures in Japan

The long-term treatment with anti-resorptive drugs for osteoporotic patients is suggested to be associated with an increase in atypical femoral fractures (AFFs). However, their incidence, patient characteristics, and risk factors have not been fully elucidated especially in Asian countries. This retrospective observational cohort study found fourteen AFFs in ten patients (four bilateral fractures) among 2,238 hip and femoral shaft fractures treated in our associated hospitals between 2005 and 2010; this incidence (0.63 %) was similar to Caucasians. Of the ten patients with AFFs, nine (90 %) and six (60 %) were using bisphosphonates (BPs) and glucocorticoids (GCs), respectively, compared to 14.3 and 8.6 % for patients with typical femoral fractures who were using these agents. As comorbid conditions, five patients had collagen disease (CD) and two had diabetes. A fracture location-, age- and gender-matched (1:3) case–control study revealed that administration of BPs, GCs, and suffering from collagen disease (CD) were significant risk factors for developing AFFs [odds ratios 36.0 (95 % confidence intervals 3.8–342.2), 13.0 (2.3–74.1) and 9.0 (1.6–50.3), respectively]. Interestingly, all of the patients with atypical subtrochanteric femoral fractures, defined as those within 5 cm of the lesser trochanter, were taking GCs due to CD, and the age of these patients (average of 54.8 years) was significantly younger than those with atypical diaphyseal femoral fractures (average of 77.2 years, p < 0.05). In conclusion, the incidence of AFFs in the Japanese population was similar to that of Caucasians, and taking BPs and GCs and suffering from CD were risk factors for developing AFFs.