Is dynamic surface electromyography topography an indication of low back pain

Abstract

Introduction: Dynamic surface electromyography (SEMG) topography was found to be altered during rehabilitation of low back pain (LBP), which tended to normal pattern with pain relief progress. SEMG topography was proposed as a quantitative and objective assessment of LBP rehabilitation. However, it is still a question whether SEMG topography is an indicator of pain or muscular strength improvement. Our hypothesis is that the change of SEMG topography is caused by pain relief instead of enhancement of muscle morphology. To verify this hypothesis, this study investigated the changes of SEMG topography immediately after local surface analgesic pain relief without changes of muscle morphology. Methods: A total of 17 patients with non-specific LBP were recruited for this study. Each patient was asked to receive a topical anesthetic spray (Yunnan Baiyao spray, Yunnan Baiyao Ltd, Yunnan, China) on the lumbar area for reducing LBP. Visual analog scale (VAS) score was evaluated before and after surface anesthetic spray. Those patients reported VAS decreased more than 2 points (including 2 points) were classified as “responder” group, while those patients reported VAS decreased less than 2 points were classified as “non-responder” group. SEMG were recorded from an electrode-array on lumbar area of patient in two groups during flexion-extension movement before and after local analgesia. SEMG topography was calculated to obtain the root-mean-square difference (RMSD) values in comparison to healthy normal pattern established with an age and gender matched group of 35 healthy subjects from a previous database. The RMSD values included RMSD of relative area (RA), relative height (RH) and relative weight (RW). The values of RMSD were compared before and after local analgesia in these two groups by paired Student’s T-test. A linear correlation analysis was performed between changes of RMSD and VAS in LBP before and after local analgesia. Results: Of 17 patients with LBP, 8 patients showed good response to local analgesia (“responder” group), while 9 patients did not show good response (“non-responder” group). The VAS score in “responder” group decreased from 4.51±1.27 to 2.18±1.27, while VAS score in “non-responder” group changed from 3.74±1.67 to 3.60±1.74. Visual inspection did not show difference in SEMG topography between “responder” and “non-responder” group. However, we could observe that the SEMG topography in “responder” group changed toward normal pattern after local analgesia. Significant higher reduction of RMSD could be seen in the “responder” group (p<0.05) in comparison to “non-responder” group. In all LBP patients, changes of RMSD RW during extension phase between local analgesia showed well correlation with reduction of VAS (r=0.532, p=0.028). Discussion: Results of this study demonstrated that the SEMG topography changed in association with pain relief after local analgesia. Since the effect of local analgesia is a loss of nociception without changes of muscle morphology, this study well verified the hypothesis that changes of SEMG topography were pain-related rather than muscular function related. If further study can verify that SEMG topography do not change in association with changes of muscle morphology, we can prove dynamic SEMG topography as an indication of low back pain.