Bisphosphonate treatment and the risk of atypical femoral fracture among patients participating in a Fracture Liaison Service of a tertiary medical center

Summary: Bisphosphonates are common treatment for osteoporosis. Among patients admitted with hip fracture, atypical femoral fractures (AFF) were more prevalent in those who were treated with Bisphosphonates for five or more years. Five years of Bisphosphonates treatment may signify an increased risk for AFF, though the absolute risk remains very low. Purpose: Atypical femoral fractures (AFF) are a rare complication of bisphosphonate (BP) treatment. We evaluated the correlation between BP exposure and AFF risk among hip fracture patients. Methods: This retrospective nested case–control study included patients over age 50 years, operated for osteoporotic hip fracture between July 2014 and November 2018, who attended our Fracture Liaison Service. We classified fracture radiographs and compared demographic, clinical, biochemical, and drug purchase data between patients with AFF and those with typical osteoporotic hip fracture (controls). To correct for the younger age of patients with AFF, we matched each case (AFF) with three controls according to age (± 1 year) and sex and performed a conditional logistic regression model. Results: Of 989 patients, 31 (3%) had AFF. Patients with AFF were younger than those with inter-trochanteric fractures (mean ± SD: 72.3 ± 10.3 vs. 80.2 ± 9.6 years, p < 0.001). Following matching, the mean Charlson’s Comorbidity Index (CCI) was lower in the AFF than in the control group (2.9 ± 3.7 vs. 4.7 ± 4.2; p = 0.030) and a higher proportion of them were treated with BP for 5 years or more (58.1 vs. 16.0%; p < 0.001). Among patients admitted with hip fracture who were treated with BP for 5 years or more, the odds ratio of this fracture being atypical was significantly higher compared with no BP treatment (21.7; 95% CI-4.1–113.9). Conclusions: Patients with AFF compared to typical hip fractures showed better baseline medical conditions irrespective of their younger age. Five years of BP treatment may be associated with an increased risk for AFF, though the absolute risk remains very low.