Sarcopenia and osteoporosis are highly prevalent syndromes in older people, characterized by loss of muscle and bone tissue, and related to adverse outcomes. Previous reports indicate mid‐thigh dual‐energy X‐ray absorptiometry (DXA) is well suited for the simultaneous assessment of bone, muscle, and fat mass in a single scan. Using cross‐sectional clinical data and whole‐body DXA images of 1322 community‐dwelling adults from the Geelong Osteoporosis Study (57% women, median age 59 years), bone and lean mass were quantified in three unconventional regions of interest (ROIs): (i) a 2.6‐cm‐thick slice of mid‐thigh, (ii) a 13‐cm‐thick slice of mid‐thigh, and (iii) the whole thigh. Conventional indices of tissue mass were also calculated (appendicular lean mass [ALM] and bone mineral density [BMD] of lumbar spine, hip, and femoral neck). The performance of thigh ROIs in identifying osteoporosis, osteopenia, low lean mass and strength, past falls, and fractures was evaluated. All thigh regions (especially whole thigh) performed well in identifying osteoporosis (area under the receiver‐operating characteristic [ROC] curve [AUC] > 0.8) and low lean mass (AUC >0.95), but they performed worse in the diagnosis of osteopenia (AUC 0.7–0.8). All thigh regions were equivalent to ALM in discrimination of poor handgrip strength, gait speed, past falls, and fractures. BMD in conventional regions was more strongly associated with past fractures than thigh ROIs. In addition to being faster and easier to quantify, mid‐thigh tissue masses can be used for identifying osteoporosis and low lean mass. They are also equivalent to conventional ROIs in their associations with muscle performance, past falls, and fractures; however, further validation is required for the prediction of fractures. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.
Purpose: The prevalence of musculoskeletal tissue loss syndromes (osteoporosis and sarcopenia), as well as obesity and their combinations, is on the rise. Previous reports indicate mid-thigh dual-energy x-ray absorptiometry (DXA) is well-suited for the simultaneous assessment of bone, muscle, and fat mass in a single scan.Methods: Using DXA images of 1322 community-dwelling adults (57% women, age 58.2 ± 15.6 SD), bone, lean and fat mass were quantified in five regions of interest (ROIs): a) a 2.6 cm; and b) a 13 cm thick slice of mid-thigh; c) whole thigh; d) whole calf; and e) forearm. Conventional indices of tissue mass i.e. appendicular lean mass, hip, and spine bone mineral density (BMD) and total, gynoid and android fat mass, were also calculated. Their associations with muscle strength (handgrip strength) and performance (timed-up-and-go [TUG] and gait speed), as well as falls and fractures, were investigated.Results: Lean mass in all ROIs was well-correlated with outcomes, and according to regression analyses, lean mass explained two-thirds, a third and a quarter of the variability in the handgrip strength (r2= 0.63 to 0.64, p<0.001), TUG (r2= 0.34 to 0.37, p<0.001) and gait speed (r2= 0.25 to 0.27, p<0.001), respectively. Lean masses were negatively associated with falls only when corrected for BMI. In the ≥60yo cohort, only mid-thigh lean mass corrected for BMI was associated with decreased odds of falls (24%, p=0.029). In all assessed ROIs, BMD was associated with the number of incident fractures within five years (OR= 0.72 to 0.93, p=0.034 to <0.001). Increased fat mass was associated with increased TUG time and decreased odds of fractures. Muscle indices corrected for BMI performed better, compared to those uncorrected or corrected for height2.Conclusion: Compared to the conventional indices and four other ROIs, mid-thigh tissue masses were associated with markers of muscle performance. Mid-thigh BMD and lean mass were superior and showed more consistent and more robust associations with adverse outcomes (falls and fractures), particularly in the older population.
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