Although atypical femoral fracture (AFF) occurs more frequently in patients taking bisphosphonates and longer treatment is associated with higher risk, the causal relationship between AFF and bisphosphonates has not been established. Most patients with AFF have osteoporosis that is being treated with bisphosphonates, but we are not aware of any reports regarding the areal bone mineral density (aBMD) and discordance between the T-scores of the femur and spine in such patients. We investigated the prevalence of aBMD discordance and the characteristics of patients with AFF.

Medical records for 63 consecutive patients treated for AFF were retrospectively evaluated, and 48 patients, all female, were eligible for the study. The average age at the time of fracture was 73.0 years, the average duration of bisphosphonate use was 68.5 months, and the average presumed age at bisphosphonate initiation was 67.2 years. We evaluated the prevalence of discordance, defined as a difference between the T-score categories of the femur and spine in the same individual as well as demographic differences between the discordance and concordance groups. We also compared the prevalence of discordance in patients with AFF with that in 114 female patients with intertrochanteric femoral fracture (ITFF).

T-score concordance, minor discordance, and major discordance were seen in 14 (29%), 32 (67%), and 2 (4%) of the patients with AFF, respectively. The prevalence of discordance was significantly higher in those with AFF (71%) than in those with ITFF (23%) (p < 0.001). The average age at bisphosphonate initiation in the AFF group was lower in the discordance group (65.7 years) than in the concordance group (70.7 years) (p = 0.04).

The prevalence of T-score discordance between the hip and lumbar spine was relatively high in patients with AFF, and the presumed age at the initiation of bisphosphonate therapy was younger in patients with discordant T-scores in this study.

Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

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