Fracture Risk Following an Atypical Femoral Fracture

Atypical femoral fractures (AFFs) occurring during the course of osteoporosis treatment usually lead to discontinuation of anti‐resorptive (AR) drugs. However, the risk of fracture after an AFF is unknown. We conducted a follow‐up study of patients with AFF matched 1:3 for age and gender with patients with a peripheral major osteoporotic fracture (pMOF), in the setting of a fracture liaison service, to investigate the incidence of subsequent low‐trauma fractures. Fifty‐five patients with AFF (95% women, age [mean ± standard deviation] 75 ± 10 years, 89% exposed to AR drugs), followed for 6.2 ± 3.7 years, were compared to 165 matched controls with a pMOF (hip 85%) followed for 4.3 ± 2.6 years. During the follow‐up, 38% of patients in the AFF group and 16% in the pMOF group received AR therapies. Continuation of AR drugs after an AFF was associated with contralateral AFF in 27% of subjects. The risks of new low‐trauma, major osteoporotic and imminent (within 2 years) fractures, were similar between the two groups: incidence rate ratio (95% confidence interval [CI]) of subsequent fracture following AFF relative to pMOF, 1.30 (95% CI, 0.82–2.04), 1.28 (95% CI, 0.74–2.15), and 1.11 (95% CI, 0.54–2.15), respectively. Moreover, the risk of sustaining multiple fractures per participant was significantly increased among patients with AFF compared to pMOF (hazard ratio 1.48 [95% CI, 1.00–2.19]; p = 0.049). When taking mortality into account, the risk of subsequent fractures tended to be higher in the AFF group (sub‐hazard ratio 1.42 [95% CI, 0.95–2.12]). In conclusion, patients who sustained an AFF are at high risk of subsequent fragility fractures, at least equal or even greater to the risk observed after a pMOF. However, continuation of AR drugs increases the risk of contralateral AFF. Therefore, optimal modalities for secondary fracture prevention after AFF require further evaluation. © 2021 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).