A number of studies have examined differences in paraspinal muscle morphology between LBP patients and controls. However, inconsistencies in the results of some of these studies may limit generalizations. The purpose of this project was to systematically review studies evaluating paraspinal muscle morphology in LBP patients and controls, with a focus on the effects of blinding. The review examined case-control studies investigating paraspinal muscle size between LBP patients and healthy controls. Studies examining the same outcome, at the same spinal level, for the same muscle and population were pooled using RevMan 5.1. Mean difference with 95% CI was calculated for each study. Eleven studies were included. All, but one pooled result were statistically significant different between groups, suggesting that paraspinal muscles are smaller in chronic LBP patients than controls, and on the symptomatic side of chronic unilateral LBP patients. In acute unilateral LBP patients there was no significant difference between sides. A qualitative examination demonstrated a trend towards an increased effect size when outcome assessors were unblinded.
The review found evidence suggested that paraspinal muscles are significantly smaller in patients with chronic LBP than in controls although no definite conclusion could be taken due to the effects of blinding.