Cortical thickness of the femur and long-term bisphosphonate use

Femoral cortical thickening has been mentioned in reports of atypical subtrochanteric/femoral shaft (ST/FS) fractures, which are associated with long-term bisphosphonate (BP) use. However, whether thickening precedes BP use or results from BP use, as well as the role BPs may play in cortical thickening remain unclear. The purpose of this study was to investigate the relationship between cortical thickness and BP use. We enrolled 142 patients (mean age 79 years) who had taken BPs for more than 5 years, and enrolled 426 osteoporosis patients who had not used BPs as controls. We performed a case-control study of patients with long-term BP use and controls matched for age, sex, and levels of activities of daily living (ADLs) (1:3 ratio). On femoral radiographs, we measured femoral cortical thickness in three regions: 5 cm and 12.5 cm below the lesser trochanter and in the region of maximal cortical thickness. We compared cortical thicknesses between patients taking BP and controls and evaluated longitudinal changes in cortical thickness. There were no significant differences in cortical thickness between long-term BP users and controls. In addition, after further use of BP for a minimum of 1 year, we observed no significant differences in the changes in cortical thickness at any level of the femur. In conclusion, our study did not find evidence of cortical thickening at the ST/FS area of the femur with long-term BP use.