Background: Inter-rater reliability of generalised lumbar extensor muscle CSA has been identified, however, more detailed reliability metrics of individual trunk muscles are lacking.
Objective: To report muscle volume and muscle fatty infiltrate (MFI) inter-rater reliability of individual trunk muscles between two novice assessors.
Methods: Lumbar axial MRI scans from 10 healthy male participants were analysed. The muscles erector spinae (ES), multifidus (M), rectus abdominis (RA), and psoas (PS) were manually traced, region of interest quantified and muscle volume and MFI determined by both assessors. Agreement between the assessors was determined using intraclass correlation coefficients (3,1), Bland-Altman plots and Lin's concordance coefficient.
Results: Good to excellent agreement was found for volume (ICC 0.77-0.96) and MFI (0.84-0.96) for all muscles on first evaluation, except for M volume, which required a second evaluation. Best agreement for muscle volume and MFI was found for ES (ICC 0.96).
Conclusions: First evaluation of muscle volume and MFI yields high to excellent inter-rater agreement, except for M, where further training and/or experience is required to achieve acceptable reliability outcomes. This may have clinical implications due to the relevance of M atrophy reported in patients with low back pain.
Keywords: Inter-rater reliability; MRI; agreement; lumbar spine; muscle.