The role of different physical function tests for the prediction of fracture risk in older women.

Abstract

Physical function is an important risk factor for fracture. Previous studies found that different physical tests (e.g., one-leg standing [OLS] and timed up and go [TUG]) predict fracture risk. This study aimed to determine which physical function test is the most optimal independent predictor of fracture risk, together with clinical risk factors (CRFs) used in fracture risk assessment (FRAX) and bone mineral density (BMD). In total, 2321 women out of the included 3028 older women, aged 77.7±1.6 (mean±SD), in the Sahlgrenska University Hospital Prospective Evaluation of Risk of Bone Fractures study had complete data on all physical function tests and were included in the analysis. At baseline, hand grip strength, OLS, TUG, walking speed and chair stand tests were performed. All incident fractures were confirmed by X-ray or review of medical records and subsequently categorized as major osteoporotic fractures (MOFs), hip fractures and any fracture. Multivariate Cox regression (hazard ratios [HRs] and 95% confidence intervals [CIs]) analyses were performed with adjustments for age, body mass index (BMI), FRAX CRFs, femoral neck BMD and all physical function tests as predictors both individually and simultaneously. Receiver operating characteristic (ROC) analyses and Fine and Gray analyses were also performed to investigate associations between physical function and incident fractures. OLS was the only physical function test to be significantly and independently associated with increased risk of any fracture (HR 1.13 [1.04-1.23]), MOF (HR 1.15 [1.04-1.26]) and hip fracture (HR 1.34 [1.11-1.62]). Adjusting for age, BMI, CRFs and femoral neck BMD did not materially alter these associations. ROC analysis for OLS, together with age, BMI, femoral neck BMD and CRFs, yielded area under the curve values of 0.642, 0.647 and 0.732 for any fracture, MOF and hip fracture, respectively. In analyses considering the competing risk of death, OLS was the only physical function test consistently associated with fracture outcomes (subhazard ratio [SHR] 1.10 [1.01-1.19] for any fracture, SHR 1.11 [1.00-1.22] for MOF and SHR 1.25 [1.03-1.50] for hip fracture). Walking speed was only independently associated with the risk of hip fracture in all Cox regression models and in the Fine and Gray analyses. Among the five physical function tests, OLS was independently associated with all fracture outcomes, even after considering the competing risk of death, indicating that OLS is the most reliable physical function test for predicting fracture risk in older women.