Optimal lumbar vertebral level for trunk muscle CT assessments in opportunistic sarcopenia screening: a cross-sectional study.

Objectives: This study aims to identify the optimal lumbar vertebral level for CT-based assessments of trunk muscles in relation to physical function and muscle strength, and to establish a foundation for opportunistic CT screening for sarcopenia.

Design: A cross-sectional study was conducted between April 2022 and December 2022. Pearson's correlation coefficients and multiple linear regression analyses were employed to estimate the correlation between CT parameters of trunk muscle with physical function and muscle strength.

Setting And Participants: The study included community residents aged 50 years and older from Kunming, Yunnan Province, China, who were part of the SOY (Sarcopenia and Osteoporosis Study of Yunnan) cohort. A total of 615 participants were enrolled, comprising 424 men and 191 women. Among these, 31 individuals (20 men and 11 women) were diagnosed with sarcopenia.

Interventions: Each participant underwent lumbar CT scanning, the Short Physical Performance Battery (SPPB) and handgrip strength (HGS) assessment.

Primary Outcome Measures: A correlation analysis was conducted for both the general and sarcopenia groups, after adjusting for age and body mass index. Additionally, a gender-stratified analysis was performed.

Results: Muscle density and muscle area at all levels exhibited a moderate correlation with grip strength, with the correlation for muscle area being more pronounced (correlation β of muscle density =0.48-0.54, p value <0.001; correlation β of muscle area=0.66-0.68, p value <0.001). However, only muscle density demonstrated a weak correlation in the correlation analysis with SPPB (correlation β of muscle density =0.09-0.12, p value <0.01). When stratified by gender, trunk muscle attenuation at the L1 vertebral level in the male group showed a more pronounced correlation with physical performance (L1-βHGS =0.25, p value <0.001 vs L2-L5-βHGS =0.16-0.19, p value =0.01-0.04; L1-βSPPB =0.31, p value <0.001 vs L2-L5-βSPPB =0.23-0.29, p value <0.01). In the female cohort, both the muscle area and muscle density at all levels showed correlations with grip strength, and the muscle area at L3 vertebrae showed the best performance (L3-βHGS =0.23, p value <0.001). In the sarcopenia group, the L1 level correlates better with HGS and SPPB than other levels. (L1-βHGS =0.54, p value =0.03 and L1-βSPPB =-0.35, p value =0.04).

Conclusions: In this study, the area and density of lumbar muscles based on CT showed correlations of varying degrees with grip strength or SPPB. The L1 layer exhibited superior performance in those aged more than 50 years, especially in the male and sarcopenia groups. This study suggests that CT-based muscle assessment at the L1 vertebra may be a feasible option for opportunistic sarcopenia screening.

Trial Registration Number: ChiCTR210005215; Pre-results.