Low Physical Function, Lean Body Mass Predict Accelerated Bone Loss After Hip Fracture

Lower physical function and lean body mass (LBM) are associated with increased risk for accelerated bone loss in older patients with previous hip fracture, according to study results published in BMC Musculoskeletal Disorders.

Researchers aimed to determine whether physical function and LBM can predict changes in the bone density and strength after a recent hip fracture in older men and women. Assessment of LBM was performed using a bioimpedance device and physical function was assessed using the Short Physical Performance Battery test and perceived difficulty in walking outdoors. Peripheral quantitative computed tomography (pQCT) measurements conducted at baseline (on average 10 weeks postfracture) and 12 months were used to assess distal tibia total volumetric bone mineral density (vBMD) and compressive bone strength index. The variables used to assess the mid-tibia were cortical vBMD and strength-strain index.

The study cohort included 81 individuals aged >60 years (mean age, 80.0 years; 78% women; mean LBM, 44.5 kg). Most men and women (64%) had a history of femoral neck fracture, while the remainder (36%) had a pertrochanteric fracture. The mean physical function score (range, 0-12) was 6.2, and 52% of the cohort had a score of <7 (low performance).

At 12 months, the mean change in distal tibia total vBMD was -1.5%±4.6% on the fractured side and 0.9%±3.7% on the nonfractured side. The mean changes for bone strength index were -2.1%±8.8% and -2.5%±7.0%, respectively.

The mean change in cortical vBMD at the mid-tibia was -1.3%±2.3% on the fractured side and -0.5%±1.6% on the nonfractured side. The respective changes for strength-strain index were -2.1%±4.4% and -1.5%±3.4%.

Multiple linear regression models showed that a lower physical function score and difficulty walking outdoors at baseline predicted greater decline in distal tibia total vBMD and distal tibia bone strength index in both legs. Greater decline in distal tibia total vBMD was also evident in patients with lower LBM at baseline.

The statistical analyses also revealed an association between a lower physical function score and LBM and a greater decline in the strength-strain index on the fractured side.

The main limitations of the study related to the observational design, as it was a secondary analysis of a randomized controlled trial. Additional limitations included missing data, a relatively small sample size, and lack of dual x-ray absorptiometry or magnetic resonance imaging data to assess LBM.

“Due to limited possibilities to prevent bone deterioration after hip fracture, attention should be paid to physical function, muscle mass preservation and fall prevention  before as well as after fracture occurrence,” concluded the researchers.

Reference

Suominen TH, Edgren J, Salpakoski A, et al. Physical function and lean body mass as predictors of bone loss after hip fracture: a prospective follow-up study. BMC Musculoskelet Disord. 2020;21(1):367.