Joint association of low bone mass and reduced relative handgrip strength with fragility fracture risk in adults aged 50–59 years: A cross-sectional study from NHANES 2013–2014

While bone mineral density (BMD) is a core indicator for fracture risk assessment, it is insufficient to fully identify truly high-risk individuals. Grip strength, as a simple indicator of muscle function, may provide additional information for fracture risk stratification, but its value during the transition from midlife to older adulthood remains unclear. This cross-sectional study analyzed 731 participants from the National Health and Nutrition Examination Survey 2013 to 2014 cycle aged 50 to 59 years. Weighted logistic regression and restricted cubic splines evaluated associations between femoral neck BMD(FN-BMD), handgrip strength (HGS (absolute and relative)), and fragility fractures. Joint stratification and exploratory receiver operating characteristic analyses were used to compare the discrimination performance of hierarchical risk models. A total of 731 participants aged 50 to 59 years were included, including 77 with fragility fractures. Absolute grip strength was not significantly associated with fragility fractures, and relative grip strength showed no significant overall or nonlinear association when analyzed as an individual continuous marker. In joint stratification analysis, participants with low femoral neck bone mineral density and low relative grip strength had the highest fracture risk (odds ratio [OR] = 3.09, 95% confidence interval [CI] 1.13-8.45, P = .028), whereas those with low bone mineral density but normal relative grip strength showed only a marginal increase (OR = 2.43, 95% CI 0.93-6.33, P = .070). Adding femoral neck bone mineral density improved discrimination (area under the curve increased from 0.615 to 0.679), whereas absolute grip strength provided minimal additional gain. In adults aged 50 to 59 years, fragility fracture risk was primarily associated with low BMD. Among individuals with low BMD, low HGS further identified a higher-risk subgroup, whereas absolute HGS provided limited incremental discriminatory value. Relative HGS may serve as a simple supplementary indicator for musculoskeletal risk assessment, but not as a standalone screening tool. These exploratory findings require validation in prospective studies with incident fracture outcomes and further evaluation of combined bone-muscle risk profiles.