INTRODUCTION: There has been increasing interest in associations between paraspinal muscle phenotypes and common spinal disorders, including lumbar spinal stenosis (LSS). However, the relation of paraspinal muscle attributes with LSS is largely unknown. Our objective was to systematically review and synthesize the current body of evidence on the association of paraspinal muscle morphology and composition as determined from imaging with LSS presence, pain severity, and disability or function.
METHODS: A systematic review was conducted, identifying relevant studies from a search of EMBASE, PubMed, SPORTDiscuss, Cinahl, Web of Science and PEDro. Relevant studies were selected, data were extracted, and risk of bias was assessed by two independent reviewers prior to conducting a narrative synthesis to summarize evidence using GRADE considerations. The study protocol was prospectively registered (Prospero: CRD42021246492).
RESULTS: Of 33 studies included in the review, multifidus (n=22) was most frequently studied, followed by the psoas muscle (n=10). Fatty infiltration (20 studies), CSA (n=11) and relative CSA (n=10) were the most studied paraspinal phenotypes. Most studies (n=31) had low risk of bias, with selection and confounding bias (n=13) most common. High variability in approaches used to measure muscle morphology and composition and LSS disability and pain, as well as variable control of confounding factors, created challenges in synthesizing findings. The only association identified for which there was moderate certainty of evidence was between increased multifidus fatty infiltration and the presence of LSS (4 of 6 studies). All other associations studied with high or moderate strength of evidence demonstrated no association, including no association between multifidus fatty infiltration and pain severity (8 studies), multifidus CSA and LSS disability (7 studies), psoas morphology and LSS anatomical severity (4 studies), or psoas composition and LSS pain severity (4 studies) for which there was high certainty. Additionally, there was moderate certainty of no association between multifidus morphology and LSS pain severity (5 of 7 studies), and between erector spinae morphology and pain severity (3 studies), and erector spinae composition and LSS pain severity (3 studies) or function (3 studies). Other associations remain more unclear.
DISCUSSION: Largely consistent results suggest multifidus fatty infiltration is associated with the presence of LSS. However, other specific associations of paraspinal muscle phenotypes on imaging and LSS pain, disability or function with high or moderate certainty of evidence demonstrated no association, and others remain largely undetermined. Although interest has grown in paraspinal muscle morphology and composition with the aim of improving phenotyping, prognosis and treatment of common spinal disorders, the clinical utility of paraspinal muscle imaging in LSS remains unclear.