Variations of CT-based trunk muscle attenuation by age, sex, and specific muscle

Abstract

Background: Fat accumulation in muscle may contribute to age-related declines in muscle function and is indicated by reduced attenuation of x-rays by muscle tissue in computed tomography scans. Reduced trunk muscle attenuation is associated with poor physical function, low back pain, and increased hyperkyphosis in older adults. However, variations in trunk muscle attenuation with age, sex and between specific muscles have not been investigated.

Methods: A cross-sectional examination of trunk muscle attenuation in computed tomography scans was performed in 60 younger (35-50 years) and 60 older (75-87 years) adults randomly selected from participants in the Framingham Heart Study Offspring and Third Generation Multidetector Computed Tomography Study. Computed tomography attenuation of 11 trunk muscles was measured at vertebral levels T8 and L3, and the effects of age, sex, and specific muscle on computed tomography attenuation of trunk muscles were determined.

Results: Muscle attenuation varied by specific muscle (p < .001), was lower in older adults (p < .001), and was generally lower in women than in men (p < .001), although not in all muscles. Age-related differences in muscle attenuation varied with specific muscle (p < .001), with the largest age differences occurring in the paraspinal and abdominal muscles.

Conclusions: Trunk muscle attenuation is lower in older adults than in younger adults in both women and men, but such age-related differences vary widely between muscle groups. The reasons that some muscles exhibit larger age-related differences in fat content than others should be further explored to better understand age-related changes in functional capacity and postural stability.

Figure 1.

Cross-sectional views of the trunk at the levels of the T8 and L3 vertebrae, indicating the muscles measured at each level and their abbreviations. Six muscles on each side were measured at T8 and eight muscles on each side were measured at L3. Three of the muscles examined were present at both levels.

Figure 2.

Mean muscle attenuation (Houndsfield units, HU) by muscle within age–sex groups at T8 (left) and L3 (right) levels of the trunk. Muscles are arranged in descending order by attenuation within each age–sex group, and error bars show +1 SD. Within each age–sex group, groups of muscles marked by the same letter do not have significantly different attenuation from each other, and thus muscles not marked by the same letter are significantly different (p < .05). See Figure 1 for definitions of muscle abbreviations.

Figure 3.

Age differences (young − older) in mean muscle attenuation by muscle at vertebral levels T8 and L3. The dashed lines show mean age difference among all muscles within each level. *Age difference for muscle is significantly different than mean age difference for all other muscles in level (p < .005 in all cases). See Figure 1 for definitions of muscle abbreviations.