Paraspinal muscle cross-sectional area predicts low back disability but not pain intensity.

BACKGROUND AND CONTEXT

The lumbar paraspinal muscles, including the erector spinae and multifidus, play an important role in movement and control of the spine. However, our understanding of their contribution to low back pain and disability is unclear. Systematic reviews have reported conflicting evidence for an association between paraspinal muscle size and low back pain, and a paucity of data examining muscle cross-sectional area (CSA) and low back disability.

PURPOSE

To investigate the relationship between paraspinal muscle CSA and both low back pain intensity and disability.

STUDY DESIGN/SETTING: One-year longitudinal cohort study.

PATIENT SAMPLE

Participants were selected from the SpineData Registry (Denmark), which enrolls people with low back pain of 2 to 12 months duration without radiculopathy and a satisfactory response to primary intervention.

OUTCOME MEASURES

Current, typical, and worst pain in the prior 2 weeks were assessed by 11-point numeric rating scales and an average pain score was calculated, and disability was measured using the 23-item Roland-Morris Disability Questionnaire. CSA (cm) of the lumbar paraspinal muscles was measured at levels L3-L5 from magnetic resonance images.

METHODS

Participants completed the study questionnaires and underwent the lumbar spine magnetic resonance images at baseline and were followed up 12 months later to repeat the questionnaires. Statistical analyses involved multivariable linear regression (cross-sectional analysis) and linear mixed-models (longitudinal analysis) with adjustment for confounders. Multiple imputation was conducted to account for missing data.

RESULTS

A total of 962 participants were included and 588 (65.8%) were followed up at 12-months. Multivariable analysis showed that greater paraspinal muscle CSA was associated with lower levels of disability, after adjusting for confounders (right mean CSA: baseline beta -0.16, 95% CI -0.26 to -0.06, p<.01; longitudinal beta -0.11, 95% CI -0.21 to -0.01, p=.03). This was evident at all levels, except L5 which was marginal at baseline (beta -0.08, 95% CI -0.15 to -0.001, p=.045) and not significant longitudinally (beta -0.05, 95% CI -0.12 to 0.02, p=.18). However, there were no associations between muscle CSA and pain intensity (baseline beta -0.02, 95% CI -0.06 to 0.02, p=.29; longitudinal beta -0.02, 95% CI -0.06 to 0.02, p=.34). Results were similar for both complete case and multiple imputation analyses.

CONCLUSIONS

This study found an inverse relationship between lumbar paraspinal muscle CSA and low back disability, but not pain intensity. While further investigation is needed, these findings suggest that treatment strategies directed at increasing paraspinal muscle size may be effective in reducing low back disability.