Trajectories of femoral neck strength in relation to the final menstrual period in a multi-ethnic cohort

Abstract

The purpose of this study was to describe the evolution of femoral neck strength relative to load across the menopause transition. It declined significantly over the 10 years bracketing the final menstrual period, and the rate of decline was modified by body mass index, race/ethnicity, and smoking status. Composite indices of femoral neck strength, which integrate dual energy X-ray absorptiometry (DXA)-derived bone mineral density and bone size with body size, are inversely associated with hip fracture risk. Our objective was to describe longitudinal trajectories of the strength indices across the menopausal transition. Data came from the Study of Women's Health Across the Nation; participants were pre- or early peri-menopausal, ages 42-53 at baseline, and were followed up for 9.1 ± 1.8 years. Composite indices of femoral neck strength in different failure modes (compression, bending, and impact) were created in 921 women who had three or more hip DXA scans and had definable final menstrual period (FMP) dates. We used mixed effects models to fit piecewise linear growth curves to the baseline-normalized strength indices as a function of time to/after the FMP. Compression and impact strength indices did not decline until 1 year prior to the FMP, and declined rapidly thereafter, with some slowing of decline 1 year after the FMP. Bending strength index increased slightly until 2 years prior to the FMP, then plateaued, and began to decline at the FMP. Mean decline in strength indices over 10 years was 6.9 % (compression), 2.5 % (bending), and 6.8 % (impact). Women with higher body mass index had larger declines in two of the three indices. Other major modifiers of rates of decline were race/ethnicity and smoking status. Femoral neck strength relative to load declines significantly during the menopausal transition, with declines commencing 1 to 2 years prior to the FMP.