Comparison of lumbar multifidus and erector spinae muscle fiber characteristics between persons with NSCLBP and healthy controls

Abstract

Introduction: The global point prevalence of low back pain (LBP) is 9.4%, with Western Europe showing the highest age-standardised prevalence. LBP is ranked highest in terms of disability and overall burden in Western Europe. Often both chronicity and non-assignable cause of pain impede the effective treatment of non-specific chronic low back pain (NSCLBP). There is accumulating evidence that macroscopic and microscopic changes in muscle structure can contribute to the development and persistency of chronic low back pain. Whilst there is growing evidence on a macroscopic level using medical imaging techniques, limited evidence exist on a microscopic level. With only one exception¹, it is not known to which extent muscle fibre type characteristics differ between healthy individuals and persons with NSCLBP.

Purpose and aim: The aim of this study was to compare muscle fiber type cross-sectional area (CSA) and percentage between individuals with NSCLBP and healthy controls for both the Erector Spinae (ES) and Multifidus (MF) muscle.

Materials and methods: Twenty persons with NSCLBP (age 44.5±7.4) and 18 healthy controls (age 39.9 ±7.9) underwent a paraspinal muscle biopsy, using a minimally invasive percutaneous technique². Biopsy samples were frozen and cut into cryosections. A multicolour immunofluorescent staining was performed using antibodies against myosin heavy chains (MHC) to visualize type I, IIa, IIax and IIx fibres. Fiber number and size were quantified using AxioVision® from ZEISS. From these values the relative muscle fiber areas (RCSA’s) were calculated. Secondary outcomes consisted of maximum oxygen uptake, back muscle strength, and activity level using the Physical Activities Scale for Individuals with Physical Disabilities (PASIPD).

Results: Persons with NSCLBP were less physically active compared to healthy controls according to the PASIPD questionnaire (p=0.0004). Back muscle strength was significantly reduced in persons with NSCLBP (p=0.0342). Maximum oxygen uptake (VO2max) did not show significant differences between both groups (p=0.1992). Persons with NSCLBP displayed a higher (p= 0.0978) percentage of type I muscle fibers, and a significant lower (p= 0.0019) percentage of type IIx muscle fibers in the ES muscle. Persons with NSCLBP also displayed a higher (p= 0.0596) RCSA for type I fibers, and a significant lower RCSA for type IIx fibers (p= 0.0441) in the ES muscle. Although not significant, a similar trend was observed in the MF muscle (figure 1).

Conclusions: This was the first study comparing muscle fiber type characteristics between persons with NSCLBP and healthy controls for both the ES and MF muscle. In summary, we found that the ES of persons with NSCLBP contained significant lower numbers of glycolytic muscle fibers, whilst the number of oxidative muscle fibers was higher compared to healthy controls. No significant between group differences were found for the MF muscle. These results are in contradiction with the available literature on paraspinal muscle fiber type composition in persons with LBP. In addition, future studies should primary focus on elucidating the mechanism by which the changes in fiber type composition are mediated in persons with NSCLBP.