Several studies have investigated differences in paraspinal muscle morphology between patients with low back pain (LBP) and control patients. However, inconsistencies in the results of some of these studies may limit generalizations.
The purpose of this study was to systematically review studies evaluating paraspinal muscle morphology in patients with LBP and control patients, with a focus on the effects of blinding.
An electronic search was performed with the use of relevant databases. Study quality was evaluated by means of the Newcastle-Ottawa Quality Assessment Scale.
Case-control studies investigating paraspinal muscle size between patients with LBP and control patients who were healthy were included. Studies that compared paraspinal muscle size between symptomatic and asymptomatic sides of patients with unilateral LBP also were included.
Studies investigating the same outcome—at the same spinal level and for the same muscle and population—were pooled. Mean differences with 95% confidence interval were calculated for each study.
Eleven studies were included. With 1 exception, all pooled results were significantly different statistically between groups, suggesting that paraspinal muscles are smaller in patients with chronic LBP than in control patients and on the symptomatic side of patients with chronic unilateral LBP. In patients with acute unilateral LBP, there was no significant difference between sides. A qualitative examination demonstrated a trend toward an increased effect size when outcome assessors were unblinded.
Limitations of this review include the small number of studies included and their small sample size. Misclassification of blinding status may have occurred when the study did not report blinding status.
Evidence suggests that paraspinal muscles are significantly smaller in patients with chronic LBP than in control patients. Although no definite conclusion could be taken as to the effects of blinding, future imaging studies should consider the use of blinded outcome assessors.