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Estimation of thigh muscle cross-sectional area by dual-energy X-ray absorptiometry in frail elderly patients^1,2,3,4

¹ From the Gastrointestinal Investigation Unit & Centre for In Vivo Body Composition, Royal North Shore Hospital, St Leonards, Australia (RDH); the School of Exercise and Sport Science, The University of Sydney, Sydney, Australia (DAW, BDL, JNG, EURS, MWT, THG, and MAFS); the Centre for Experimental Radiation Oncology, Cancer Care Centre, St George Hospital, Kogarah, Australia (BJA); Balmain Hospital, Balmain, Australia (NAS and TMS); the Department of Aged Care & Rehabilitation Medicine, Royal North Shore Hospital, St Leonards, Australia (TPF); St George Hospital, Kogarah, Australia (THD and PIS); the Faculty of Medicine, University of New South Wales, Sydney, Australia (ADD); and Hebrew SeniorLife and the Jean Mayer US Department of Agriculture Human Nutrition Research Center on Aging at Tufts University, Boston, MA (MAFS)

Background: Thigh muscle mass and cross-sectional area (CSA) are useful indexes of sarcopenia and the response to treatment in older patients. Current criterion methods are computed tomography (CT) and magnetic resonance imaging.

Objective: The objective was to compare thigh muscle mass estimated by dual-energy X-ray absorptiometry (DXA), a less expensive and more accessible method, with thigh muscle CSA determined by CT in a group of elderly patients recovering from hip fracture.

Design: Midthigh muscle CSA (in cm²) was assessed from a 1-mm CT slice and midthigh muscle mass (g) from a 1.3-cm DXA slice in 30 patients (24 women) aged 81 ± 8 y during 12 mo of follow-up. Fat-to-lean soft tissue ratios were calculated with each technique to permit direct comparison of a variable in the same units.

Results: Baseline midthigh muscle CSA was highly correlated with midthigh muscle mass (r = 0.86, P < 0.001) such that DXA predicted CT-determined CSA with an SEE of 10 cm² (an error of 12% of the mean CSA value). CT- and DXA-determined ratios of midthigh fat to lean mass were similarly related (intraclass correlation coefficient = 0.87, P < 0.001). When data were expressed as the changes from baseline to follow-up, CT and DXA changes were weakly correlated (intraclass correlation coefficient = 0.51, P = 0.019).

Conclusions: Assessment of sarcopenia by DXA midthigh slice is a potential low-radiation, accessible alternative to CT scanning of older patients. The errors inherent in this technique indicate, however, that it should be applied to groups of patients rather than to individuals or to evaluate the response to interventions.

Key Words: Sarcopenia • midthigh muscle mass • dual-energy X-ray absorptiometry • hip fracture • frail elders