Assessment of bone microarchitecture in postmenopausal women on long-term bisphosphonate therapy with atypical fractures of the femur.

Reports of atypical femoral fractures (AFFs) in patients receiving long- term bisphosphonate therapy have raised concerns regarding the genesis of this rare event. Using high-resolution peripheral quantitative computed tomography (HR-pQCT), we conducted a study to evaluate bone microarchitecture in patients who had suffered an AFF during long-term bisphosphonate treatment. The aim of our study was to evaluate if bone microarchitecture assessment could help explain the pathophysiology of these fractures. We compared bone volumetric density and microarchitectural parameters measured by HR-pQCT in the radius and tibia in 20 patients with AFFs with 35 postmenopausal women who had also received long-term bisphosphonate treatment but had not experienced AFFs, and with 54 treatment-naive postmenopausal women. Control groups were similar in age, body mass index (BMI), and bone mineral density (BMD). Mean age of the 20 patients with AFFs was 71 years, mean lumbar spine T-score was -2.2, and mean femoral neck T-score was -2. Mean time on bisphosphonate treatment was 10.9 years (range, 5-20 years). None of the patients had other conditions associated with AFFs such as rheumatoid arthritis, diabetes or glucocorticoid use. There were no statistically significant differences in any of the parameters measured by HR-pQCT between postmenopausal women with or without treatment history and with or without history of atypical fractures. We could not find any distinctive microarchitecture features in the peripheral skeleton of women who had suffered an atypical fracture of the femur while receiving bisphosphonate treatment. This suggests that risk of developing an atypical fracture is not related to bone microarchitecture deterioration. Our results indicate that there may be other individual factors predisposing to atypical fractures in patients treated with bisphosphonates, and that those are independent of bone microarchitecture. In the future, identification of those factors could help prevent and understand the complex physiopathology of these rare events.