Lateral cortical thickening and bone heterogeneity of the subtrochanteric femur measured with quantitative CT as indicators for early detection of atypical femoral fractures in long-term bisphosphonate users

OBJECTIVE. The objective of our study was to compare subtrochanteric femur bone mineral density (BMD) and bone quality of long-term bisphosphonate (BP) users who sustained an atypical femoral fracture (AFF) with BP users who did not sustain a femoral fracture and BP-nave patients with no history of femoral fracture using quantitative CT (QCT). MATERIALS AND METHODS. Fourteen female BP users with an AFF (mean age, 72.6 years; mean duration of BP use, 6.2 years; mean body mass index, 21.9) who had undergone QCT before fracture events were sex-, age-, BP use duration-, and body mass index-matched to 14 BP users who did not sustain a fracture and 14 BP-naive patients. The lateral cortical thickness index (CTI) and the mean BMD (BMD_mean) and SD of the BMD (BMD_SD) within the lateral cortex and within the entire cross-sectional area of the subtrochanteric femur were measured on axial QCT. Femoral neck-shaft angles were measured on the QCT scout image. Parameters were analyzed using the Kruskal-Wallis test. RESULTS. Lateral CTIs were greater in the BP users with an AFF (median, 0.28) than in the BP users without a femoral fracture (median, 0.21) (p = 0.038) and the BP-naive group (median, 0.21) (p = 0.009). The lateral cortex BMD_SD was significantly higher in the BP users with an AFF (median, 59.59 mg/cm3) than the BP users without a femoral fracture (median, 39.27 mg/cm3; p = 0.049) and the BP-naive group (median, 31.02 mg/cm3; p = 0.037). There was no significant difference among groups in lateral cortex BMD_mean, BMD_mean and BMD_SD of the entire cross-sectional area, and femoral neck-shaft angle. CONCLUSION. Long-term BP users with a subsequent AFF had a thicker lateral cortex and higher lateral cortex BMDSD at the subtrochanteric area before the fracture on QCT than BP users who did not sustain a femoral fracture and BP-naive patients.