Degenerative spinal pathology is associated with altered lumbar multifidus muscle morphology: a cross-sectional study of patients attending a public outpatient spine clinic with low back or leg pain.

Abstract Background: There is ongoing interest in assessing the lumbar multifidus muscles to determine their role in patients with non-specific low back pain. While associations between lumbar-related pain, altered multifidus morphology, and/or degenerative pathologies have been implied, it is unknown how these associations may be influenced by the severity, number, or distribution of pathologies. This study explores the associations of degenerative lumbar magnetic resonance imaging (MRI) findings, both individually and in combination, to multifidus muscle morphology. Methods: Cross-sectional study in a secondary care setting. Outpatient spinal clinic patients, 17 to 72 years of age, presented with a primary complaint of low back and/or leg symptoms. MRI-based average percentage pure multifidus muscle cross-sectional area (% MCSA) at L4 and L5, and the worst % MCSA measures at L4 or L5, were acquired. Univariable and multivariable linear regression models, adjusted for age, sex and BMI, investigated for cross-sectional associations between the presence, distribution, and/or severity of MRI-identified lumbar degenerative pathologies (both individually and in aggregate) and the outcome measures. Results were reported with unstandardized beta coefficients and [95% confidence intervals].Results: Data from 522 patients [294 females; mean (SD) age: 43.6 (9.8) years] were included. The average and worst % MCSA were lower in the presence of each type of pathology, as the severity or distribution increased, and as the number of different pathologies increased. Multivariable analysis identified disc degeneration at two or more levels (average: -4.51 [-6.72; -2.3]; worst: -4.32 [-6.52; -2.12]), Modic type 2 changes (average: -4.06 [-6.09; -2.04]; worst: -4.35 [-6.36; -2.35]), endplate defects (average: -2.74 [-4.58; -0.91]; worst: -2.18 [-4.0; -0.36]), facet joint arthrosis (average: -4.02 [-6.26; -1.78]; worst: -3.78 [-6.01; -1.54]), and moderate to severe disc herniations (average: -3.66 [-5.8; -1.52]) as being associated with lower % MCSA. The presence of 6 or more pathologies demonstrated the greatest % MCSA difference for all variables (average: -6.77 [-9.76; -3.77]; worst: -6.28 [-9.28; -3.28]), supporting a potential dose-response relationship between spinal pathology and LMM morphology.Conclusions: Significant associations were identified between disc degeneration, facet joint arthrosis, Modic type 2 marrow changes, an increasing aggregate of pathologies, and lower % MCSA. These associations could hypothetically indicate that the spinal and muscle findings: 1) are both part of the same degenerative process, 2) both result from prior injury or other common antecedent events, or 3) may contain a directional relationship. Future longitudinal studies are needed to further examine the complex nature of these relationships, taking into account the type, severity, total levels affected, and total number of different pathologies present.