Is there a definition of low lean mass that captures the associated low bone mineral density? A cross-sectional study of 80 men with hip fracture

BACKGROUND AND AIMS: Subjects with osteosarcopenia, the concurrent presence of sarcopenia and osteoporosis, have prognostic disadvantages and can benefit from treatments targeted at both the conditions. Our aim was to elucidate whether the available definitions of low appendicular lean mass (aLM) capture or not the men with associated low bone mineral density (BMD) following a hip fracture. METHODS: 80 men admitted to our rehabilitation hospital underwent a dual-energy X-ray absorptiometry scan 19.1 ± 4.1 (mean ± SD) days after hip fracture occurrence. Low aLM was identified according to either Baumgartner's definition (aLM/height2 < 7.26 kg/m2) or the criteria from the Foundation for the National Institutes of Health (FNIH): aLM < 19.75 kg, or aLM adjusted for body mass index (BMI) < 0.789. Low BMD was diagnosed with a T-score < - 2.5 at the unfractured femur. RESULTS: We found a significant positive correlation between aLM and BMD assessed at either femoral neck (r = 0.44; p < 0.001) or total hip (r = 0.50; p < 0.001). After categorization according to the FNIH threshold for aLM, we found a significant association between low aLM and low BMD: χ2(1, n = 80) = 5.4 (p = 0.020), which persisted after adjustment for age and fat mass. Conversely, categorization according to neither Baumgartner's threshold for aLM/height2 nor to the FNIH threshold for aLM/BMI was associated with low BMD. CONCLUSIONS: The association between low aLM and low BMD in men with hip fracture dramatically depends on the adopted definition of low aLM. FNIH threshold for aLM (< 19.75 kg) emerges as a useful tool to capture men with damage to both the components of the muscle-bone unit.