SUN-355 Associations of Trabecular Bone Score and Bone Mineral Density with Cardiorespiratory Fitness and Body Composition in Men with and Without Paraplegia

Introduction: Following spinal cord injury (SCI) lower extremity bone mineral density (BMD) losses are as high as 40% due to mechanical unloading and autonomic dysfunction. While lumbar spine (LS) BMD appears to be relatively spared, evidence suggests BMD by dual-energy radiographic absorptiometry (DXA) may overlook bone pathology in this region. Trabecular Bone Score (TBS), representative of bone microarchitecture, may be a more informative measurement of LS pathology in SCI. Our objective was to determine differences in BMD and TBS within the LS in humans with and without SCI. Correlation of fitness and body composition measures with TBS and BMD were also explored to determine their role in bone health after SCI. Methods: Seven male participants with paraplegia (level T3 – T7) were recruited through The Miami Project to Cure Paralysis, and 6 males without SCI were recruited from local advertisement. DXA scans of the lumbar spine and whole body were performed using Hologic Discovery A densitometer. TBS score (unitless) was derived from L1-L4 scans using TBS iNsight software v3.0.2. A graded arm exercise test directly measured cardiorespiratory fitness (VO(2)peak) for all subjects. An independent samples t-test determined between-group differences in LS BMD and TBS. Pearson correlation analysis investigated within-group relations among LS BMD, TBS and VO(2)peak (ml/kg/min), weight (kg), total body fat (%), and visceral adipose tissue (estimated VAT mass(g)). Results: In SCI, the mean duration of injury was 8.6 years. Mean LS BMD was not different (p=.47) between non-injured (1.10 ±0.11 g/cm(2)) and SCI (1.10 ±0.13 g/cm(2)) groups. However, mean TBS score was different (p=.053) between non-injured (1.55±0.09) and SCI (1.47±0.07) groups. In non-injured, VO(2)peak was correlated with LS BMD (r=.356) and TBS (r=.244). In SCI, VO(2)peak was correlated with LS BMD (r=.111) and TBS (r=.822). In non-injured, TBS was correlated with body mass (r=.244), total body fat (%) (r=.382), and visceral adipose tissue (r=.361). In SCI, negative correlations were observed; TBS was correlated with body mass (r= -.255), total body fat (%) (r= -.474), and visceral adipose tissue (r= -.513). LS BMD was positively correlated with body mass, total body fat (%) and visceral adipose tissue in both non-injured and SCI groups. Conclusion: Men with and without SCI displayed similar BMD but differed in TBS at the LS. Correlations with measures of fitness and body composition were similar for LS BMD but discordant for TBS between non-injured and SCI groups. The data suggest changes in the relationships between cardiorespiratory fitness, metabolism and bone quality in SCI. TBS may capture alterations in bone microarchitecture at the spine after SCI that are undetected by conventional DXA.