Multifidus and paraspinal muscle group cross-sectional areas of patients with low back pain and control patients: a systematic review with a focus on blinding

Abstract

Background: 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.

Objective: 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.

Data sources: An electronic search was performed with the use of relevant databases. Study quality was evaluated by means of the Newcastle-Ottawa Quality Assessment Scale.

Study selection: 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.

Data extraction: 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.

Data synthesis: 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: 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.

Conclusions: 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.

Figure 1.

Flowchart of systematic review inclusion and exclusion of case-control and symptomatic/asymptomatic studies. LBP=low back pain.

Figure 2.

Mean differences and 95% confidence intervals (95% CIs) of blinded and unblinded studies evaluating multifidus muscle cross-sectional area (in square centimeters) at (A) L4 and (B) L5 between patients with chronic low back pain (LBP) and control patients. IV=inverse variance.

Figure 3.

Mean differences and 95% confidence intervals (95% CIs) of blinded and unblinded studies evaluating paraspinal muscle group cross-sectional area (in square centimeters) at L4–L5 or lower L4 between patients with chronic low back pain (LBP) and control patients. IV=inverse variance.

Figure 4.

Mean differences and 95% confidence intervals (95% CIs) of blinded and unblinded studies evaluating paraspinal muscle group cross-sectional area ratio at L4–L5 or lower L4 between patients with chronic low back pain (LBP) control and control patients. IV=inverse variance.

Figure 5.

Mean differences and 95% confidence intervals (95% CIs) for symptomatic/asymptomatic studies comparing (A) multifidus muscle cross-sectional area (CSA) (in square centimeters) between sides in patients with acute low back pain (LBP) at the pathologic spinal level, (B) multifidus muscle CSA or functional CSA (in square centimeters) between sides in patients with chronic LBP at level below lumbar pathology, and (C) multifidus muscle CSA or functional CSA (in square centimeters) between sides in patients with chronic LBP at the pathologic spinal level. IV=inverse variance.

Appendix.

Search Strategies

Appendix.

Search Strategies