Importance of Lumbar Instability in the Study of Associations Between Muscle Morphology, Pain, and Disability in Chronic Low Back Pain

Abstract

Objective: The purpose of this study was to (1) evaluate the relationship between lumbar extensor muscle morphology, with pain and disability in patients with chronic low back pain and (2) compare these relationships in subgroup of chronic low back pain with and without lumbar structural segmental instability.

Design and methods: This cross-sectional study included 183 patients with chronic low back pain. Standing lateral lumbar flexion/extension radiographs were used to assess lumbar structural segmental instability. Lumbar multifidus, erector spinae, and psoas major morphology were determined from axial magnetic resonance imaging. Associations between lumbar muscle morphologies and patient pain and disability were evaluated in two groups with and without lumbar instability.

Results: Patients' disability was negatively associated with psoas major total cross-sectional area (beta = -22.82, 95% CI = -37.05 to -8.59) and functional cross-sectional area (beta = -23.45, 95% CI = -37.81 to -9.09). Multifidus morphology was negatively associated with disability in the lumbar instability group. Pain intensity was only associated to psoas major total cross-sectional area (beta = -3.33, 95% CI = -6.43 to -2.24) and functional cross-sectional area (beta = -3.22, 95% CI = -6.40 to -0.05) only in the lumbar instability group.

Conclusions: Psoas major atrophy was associated with greater disability and pain in chronic low back pain, but multifidus atrophy was associated with greater disability in chronic low back pain patients with lumbar structural segmental instability.