Background/Purpose: Atypical femoral fractures (AFFs) are a rare complication of bisphosphonate use and a major reason that drug holidays are recommended following bisphosphonate use. However, the extent to which post-fracture complications occur in AFFs compared to subtrochanteric femoral fractures (SFF) and typical hip fractures (THF) is not clear. This study aims to determine if time without complication differs among AFF, SFF and THF.

Methods: We conducted a retrospective study of adults aged > 50 years old who used oral or IV bisphosphonates between October 1, 1999 and December 31, 2022 in the VHA Corporate Data Warehouse who had AFF, SFF, or THF. Those with ESRD, metabolic bone diseases other than osteoporosis, cancer, a filled prescription for etidronate, pamidronate or tiludronate or those whose dose of zoledronic acid was or < 273 days from the initial dose were excluded. Among these patients, we used ICD-9-CM and ICD-10-CM codes to find complications of fractures including osteomyelitis, pressure ulcers, fracture nonunion, and fracture malunion within 12 months of diagnosis. We then used an unadjusted semiparametric accelerated failure time (AFT) model to determine the time to complication among each cohort. We adjusted the results for age at first prescription of bisphosphonate script (FPOS), White vs. non-White racial identity, ethnicity, BMI, Charleston Comorbidity Index, VA Frailty Index, and smoking status.

Results: Of the 5,650 patients who met inclusion criteria, 21 experienced an AFF (with a median age of 68 at FPOS, and 9.52% non-White), 255 experienced a SFF (with a median age of 70 at FPOS, and 11.7% non-White), and 5,374 experienced a THF (with a median age of 75 at FPOS, and 8.19% non-White). Within 12 months of the fracture, only 1 person (4.76%) with an AFF experienced a complication (a fracture nonunion), compared to 22 (8.63%) with SFF and 283 (5.27%) with a THF. The number of complications in each group were too small to compare rates for each complication directly.Overall time to complication did not differ between the three groups. The average time without complication following SFF was 0.520 times that for THF (95% CI: 0.455 to 0.596, p ≈ 0). The average time without complication following AFF did not differ from THF (95% CI: 0.186 to 23.584, p = 0.549).After adjusting for the above covariates, the average time without any complication following SFF was 0.381 times the estimated time without any complication following THF (95% CI: 0.190 to 0.765, p = 0.007). Adjusting for the same variables, the estimated time without complication following AFF did not differ from estimated time without complication following THF (95% CI: 0.056 to 35.875, p = 0.831).

Conclusion: The adjusted average time to complication is shorter in patients with SFF compared to THF. However, the adjusted average time to complication in patients with AFF does not differ from those with THF.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/complication-rates-of-typical-hip-fractures-subtrochanteric-femoral-fractures-and-atypical-femoral-fractures/