From: Spine (Phila Pa 1976). 2010 Jun 24. [Epub ahead of print]
To determine the reproducibility of the cervical flexion-relaxation ratio measured 4 weeks apart in a group of chronic neck pain patients and healthy control group and to compare the flexion-relaxation ratio between the 2 groups. The cervical flexion-relaxation ratio measures the ability of the neck extensor muscles to relax during forward flexion, similar to the lumbar flexion-relaxation ratio. The flexion relaxation phenomenon is commonly defined as a decrease in superficial paraspinal muscle electromyography (EMG) signals that occur just before full trunk flexion. Its reliability and ability to discriminate neck pain patients from controls has not been investigated.
Fourteen participants with chronic neck pain and a control group of 14 individuals with no neck pain were recruited via advertisement and word of mouth. The cervical flexion-relaxation ratio was determined at baseline and 4 weeks later using standardized electromyographic data collection and analysis procedures. The mean flexion-relaxation ratio value for the combined left and right side data for the neck pain groups was 1.93 +/- 0.8, and 1.73 +/- 0.61 at 4-week follow-up. The intraclass correlation coefficient (ICC) was 0.83 (95% CI = 0.67-0.92). Three participants in the control group developed neck pain in the 4 weeks and their data were not included in the reliability calculation. For the control group, the combined (left and right side) mean flexion-relaxation ratio value was 4.09 +/- 1.58 at baseline and 4.27 +/- 1.71 on retest 4 weeks later. The ICC (intraclass r) was 0.89 (95% confidence interval = 0.76-0.95). The overall ICC for the combined groups was 0.92 (95% confidence interval = 0.86-0.95). An independent 2 group t test revealed a significant difference in the baseline flexion-relaxation ratio data between the control group and the neck pain group (P < 0.001).
The cervical extensor muscles exhibit a consistent flexion-relaxation phenomenon in healthy control subjects and the measurement is highly reproducible when measured 4 weeks apart in both controls and chronic neck pain patients. The flexion-relaxation ratio in neck pain patients is significantly higher than in control subjects suggesting that this measure may be a useful marker of altered neuromuscular function.