Qualitative and quantitative characteristics of the lumbar multifidi muscles: Comparison of the magnetic resonance imaging and musculoskeletal ultrasound.

Background: Paraspinal muscle pathology is often accompanied by skeletal abnormalities and is frequently associated with low back pain. While magnetic resonance imaging (MRI) can accurately assess muscle atrophy, the utility of musculoskeletal ultrasound remains under evaluation. A direct comparison between these imaging modalities has not been conducted. Objective: To compare musculoskeletal ultrasound and MRI in evaluating fatty atrophy and cross-sectional area in patients with chronic low back pain and to assess their correlations with clinical symptoms. Methods: The degree of fatty atrophy and cross-sectional area were measured using ultrasound at symptomatic and control levels in patients with chronic low back pain. A prone instability test was also performed. Ultrasound findings were compared with recent lumbar MRI results. Fatty atrophy was graded using the Kjaer system, and cross-sectional area was measured. Interobserver agreement and correlation with the available imaging were calculated. Results: Strong agreement was observed with MRI for the degree of atrophy at the symptomatic level (weighted Kappa = 0.83), but only fair agreement at the control level. Cross-sectional measurements showed poor correlation between the imaging studies at both levels (Rho = 0.03-0.07). The prone instability test was negative for all participants. Conclusion: Ultrasound reliably assesses fatty atrophy at symptomatic levels but is less accurate for circumferential measurements.