Publications

Background: Low back pain (LBP) is one of the most common musculoskeletal conditions. People with LBP often display changes of neuromuscular control and trunk mechanical properties, including trunk stiffness. Although a few individual studies have examined back muscle stiffness in individuals with LBP, a synthesis of the evidence appears to be lacking. Therefore, the aim of this systematic review with meta-analysis was to synthesize and evaluate the available literature investigating back muscle stiffness in association with LBP.

Methods: We conducted a systematic review of the literature according to the PRISMA guidelines. We searched Pubmed, Scopus, Web of Science and ScienceDirect for studies, that compared back muscle stiffness, measured either by ultrasound-based elastography or myotonometry, between individuals with and without LBP. Pooled data of the included studies were presented descriptively. Additionally, we performed two meta-analyses to calculate the standardized mean difference between the two groups for resting stiffness of the multifidus and erector spinae muscle. For both meta-analyses, the random effect model was used and the weight of individual studies was calculated using the inverse-variance method. The quality of the included studies was assessed using the Joanna Briggs Institute Critical Appraisal Checklist for Analytical Cross-Sectional studies. Furthermore, the certainty of evidence was evaluated using the GRADE approach.

Results: Nine studies were included in our systematic review. Our results suggest that individuals with LBP have higher stiffness of the multifidus (SMD = 0.48, 95% CI: 0.15 – 0.81, p < 0.01; I2 = 48 %, p = 0.11) and erector spinae at rest (SMD = 0.37, 95% CI: 0.11 – 0.62, p < 0.01; I2 = 39 %, p = 0.14) compared to asymptomatic controls. On the other hand, the evidence regarding muscle stiffness during submaximal contractions is somewhat contradictory.

Conclusions: Based on the findings of this systematic review we conclude that people with LBP may have higher back muscle stiffness compared to asymptomatic controls. Addressing muscle stiffness might represent an important goal of LBP treatment. Nevertheless, our findings should be interpreted with extreme caution due to a limited quality of evidence, small number of included studies and differences in measurement methodology.

Keywords: muscle properties, neuromuscular control, low back disorders, elastography, myotonometry

The aim of this systematic review with meta-analysis was to investigate changes in trunk muscle stiffness in relation to LBP. Our findings suggest that there is low to moderate certainty of evidence of higher resting MF and ES stiffness in individuals with LBP compared with asymptomatic controls. On the other hand, evidence for altered MF stiffness during submaximal contraction is somewhat conflicting. All things considered, we advise extreme caution when interpreting our study results, due to a limited certainty of evidence, small number of included studies and differences in methodology of tissue stiffness assessment.

Practical implications: Increased back muscle stiffness could play a role in the persistence of symptoms and could represent a potential treatment goal in LBP management. Additionally, muscle stiffness may be used as an outcome measure for the evaluation of progress in patients with LBP.