Physical function and lean body mass as predictors of bone loss after hip fracture: a prospective follow-up study.

BACKGROUND: Predictors of bone deterioration after hip fracture have not been well characterized. The aim of this study was to examine the associations of physical function and lean body mass (LBM) with loss of bone density and strength in older people recovering from a hip fracture. METHODS: A total of 81 over 60-year-old, community-dwelling men and women operated for a hip fracture participated in this 1-year prospective follow-up study. Distal tibia total volumetric bone mineral density (vBMDTOT, mg/cm3) and compressive strength index (BSI, g2/cm4) and mid-tibia cortical vBMD (vBMDCO, mg/cm3) and bending strength index (SSI, mm3) were assessed in both legs by peripheral quantitative computed tomography (pQCT) at baseline (on average 10 weeks after fracture) and at 12 months. At baseline, LBM was measured with a bioimpedance device and physical function with the Short Physical Performance Battery (SPPB) and perceived difficulty in walking outdoors. Robust multivariable linear regression models were used to estimate the associations of physical function and LBM with the change in bone parameters at 12-months. RESULTS: The mean change in distal tibia vBMDTOT and BSI in both legs ranged from - 0.9 to - 2.5%. The change in mid-tibia vBMDCO and SSI ranged from - 0.5 to - 2.1%. A lower SPPB score, difficulty in walking outdoors and lower LBM predicted greater decline in distal tibia vBMDTOT in both legs. A lower SPPB score and difficulty in walking outdoors were also associated with a greater decline in distal tibia BSI in both legs. At the midshaft site, a lower SPPB score and lower LBM were associated with greater decline in SSI on the fractured side. CONCLUSIONS: Older hip fracture patients with low physical function and lower LBM may be at risk for greater decline in tibia bone properties during the first post-fracture year. Acknowledgement of the risk factors could assist in developing interventions and care to promote bone health and overall recovery. TRIAL REGISTRATION: ISRCTN, ISRCTN53680197. The trial was registered retrospectively but before the recruitment was completed. Registered March 3, 2010.