Lumbar paraspinal muscles in patients with chronic non-specific low back pain and the effect of exercise: comparative and interventional study

Viktoria Kokosova^1,2Daniela Vlazna^1,2,3Peter Krkoška¹Michaela Sládečková^1,2,3Marek Dostál^4,5Katerina Matulova²Gerstberger Radim⁴Petra Ovesna⁶Blanka Adamova^1,2*

• ¹Department of Neurology, University Hospital Brno, Brno, Czechia
• ²Faculty of Medicine, Masaryk University, Brno, Czechia, Brno, Czechia
• ³Department of Rehabilitation, University Hospital Brno, Brno, Czechia, Brno, Czechia
• ⁴Fakultni nemocnice Brno Klinika radiologie a nuklearni mediciny, Brno, Czechia
• ⁵Department of Biophysics, Faculty of Medicine, Masaryk University, Brno, Czechia, Brno, Czechia
• ⁶Institute of Biostatistics and Analyses, Brno, Czechia, Brno, Czechia

Background: Lumbar paraspinal muscles (LPM), which belong to lumbar extensor muscles, play a key role in stabilising the lumbar spine and maintaining spine health. Although chronic non-specific low back pain (CNLBP) represents a major health problem worldwide, there is a knowledge gap regarding the function, morphology of LPM, and the effect of regular exercise on them in patients with CNLBP. The purpose of the study was to evaluate functional and quantitative MRI (qMRI) parameters of LPM in CNLBP patients, compare them to matched healthy volunteers (HV), and assess the effect of exercise therapy on these parameters in CNLBP patients. Methods: The first part of the study was cross-sectional, observational, and comparative; the second was prospective and interventional. Based on physiological parameters, 43 matched pairs of CNLBP patients and HV were formed. All participants underwent MRI of the LPM using a 6-point Dixon gradient-echo sequence to assess qMRI parameters: fat fraction, total muscle volume, and functional muscle volume (FMV). Maximal isometric lumbar extensor muscle strength (MILEMS), lumbar extensor muscle endurance (LEME), MILEMS to LPM FMV ratio, pain, and disability were assessed. Each group's parameters were compared and effect size evaluated. The total of 29 patients entered an 18-week hybrid guided daily home-based exercise programme, which was completed by 27 CNLBP patients. The study was registered, trial registration number is ISRCTN11556477. Results: CNLBP patients had significantly lower MILEMS, LEME (both P<0.001), and MILEMS to LPM FMV ratio (P=0.006) compared to matched HV. These parameters, as well as pain and disability, improved significantly after exercise (each P<0.001). The qMRI parameters did not differ between CNLBP patients and HV, nor did they change after exercise therapy. Conclusions: The significant LPM dysfunction and poorer muscle quality in CNLBP patients were reversible with exercise. Our study does not support the use of qMRI parameters as objective and reliable biomarkers of LPM dysfunction in a cohort of CNLBP with mild clinical impairment.