Abstract
Background and Purpose: Ultrasound (US) imaging may be a cost-conscious alternative to magnetic resonance imaging (MRI), which is the criterion standard for muscle cross-sectional area (CSA) assessment. Within the trunk, when compared with MRI, US has been shown to be valid for assessing lumbar multifidi CSA in younger, asymptomatic individuals. To date, there are no studies validating US for multifidi CSA assessment in older adults or individuals with low back pain. Given age- and pain-related muscle changes, validation of US is needed in these populations. If valid for multifidi CSA assessment, US may be used to evaluate short-term changes in muscle size in response to exercise-based interventions among older adults. The primary objective of this study was to evaluate the validity of US for multifidi CSA assessment as compared with MRI in older adults with and without chronic low back pain (CLBP). The secondary objective was to determine whether a single US image was valid for assessment of multifidi CSA or whether the average of 3 US images should be recommended.
Methods: Twenty community-dwelling older adults (ie, 10 with and 10 without CLBP), ages 60 to 85 years, were recruited. US images and MRI slices of multifidi muscle were obtained and L4 multifidi CSAs were measured. Intraclass correlation coefficients (ICCs) were calculated to assess agreement between MRI measures and a single US image and MRI measures and the average of 3 US images.
Results and Discussion: ICC point estimates were excellent for older adults with CLBP for a single US image (ICCs = 0.90-0.97), but ICC point estimates for participants without CLBP ranged from fair to excellent (ICCs = 0.48-0.86). ICC point estimates for the average of 3 US images for both groups were better than for a single image (ICCs = 0.95-0.99).
Conclusions: For assessment of L4 multifidi CSA, US is a valid alternative to MRI for older adults with and without CLBP. However, limitations of US, such as the inability to quantify intramuscular fat, which may be increased with aging and CLBP, should be considered. CSA measurement of 3 US images, rather than a single image, is recommended.