Unilateral changes of the multifidus in persons with lumbar disc herniation: a systematic review and meta-analysis

BACKGROUND: Lumbar disc herniation (LDH) is one of the most often diagnosed degenerative pathologies within the lumbar spine. Paraspinal muscle involvement could be a possible mediator in the pathophysiology of disc herniation and influences the course of pain and disability after both surgical or nonsurgical treatment. To potentially improve treatment, it may be important to assess multifidus muscle morphology in patients diagnosed with a LDH. OBJECTIVE: A systematic literature review and meta-analysis regarding the multifidus morphology in patients diagnosed with a LDH was conducted to assess the differences in multifidus muscle morphology between persons with LDH and healthy controls, and between the involved and the uninvolved side within subjects experiencing unilateral LDH. METHODS: A systematic search was conducted of articles published up to and including November 2019 using the Pubmed, Web of Science, EMBASE, and MEDLINE Ovid search engines. The articles obtained from this search were screened based on title and abstract using the predetermined eligibility criteria. Included full text articles were assessed for their methodologic quality using the modified Downs and Black checklist. Heterogeneous data regarding multifidus muscle morphology was included in the descriptive analysis; data that was homogenous was included in the meta-analysis. RESULTS: We identified 3,176 articles. Based on the screening for inclusion/exclusion criteria, 18 articles were included. Studies were either cross sectional or case-control studies assessing side-toside differences or comparing patients diagnosed with a LDH to a healthy control group. Nine studies investigated whole muscle atrophy, six looked at muscle fat infiltration, seven studies assessed microscopic muscle properties including muscle fiber size, distribution, and muscle fibrosis. From the 18 articles, 10 were included in the meta-analysis. In the meta-analysis, a comparison was made between side-to-side differences for muscle fiber size, distribution, and whole muscle size. Descriptive analysis showed increased fat infiltration and atrophy (muscle and individual fiber) of the multifidus muscle when comparing side-to-side differences or comparing cases to controls. Meta-analysis showed a significant decrease in type I and II muscle fiber size (p=.002, .01, respectively) combined with a significant increase in the number of type I muscle fibers (p=.008) at the side of LDH. Regarding whole muscle size, no significant differences were found. CONCLUSIONS: This study shows the presence of ipsilateral multifidus muscle changes in persons with unilateral LDH. (C) 2020 Elsevier Inc. All rights reserved.