Resting electromyographic activity of deep thoracic transversospinalis muscles identified as abnormal with palpation.

CONTEXT In the 1940s, osteopathic researchers suggested that paraspinal tissue abnormality was associated with spontaneous muscle activity, but few studies have since re-examined these reports. OBJECTIVE To determine whether abnormal motor activity plays a role in deep paraspinal tissues that appear abnormal to palpation. METHODS Using an observational study design, the PVG of participants with thoracic pain were palpated by two examiners for consensus on the most marked level of tissue abnormality. Dual fine-wire, intramuscular electrodes were inserted into the deep transversospinalis (multifidus, rotatores) muscles at the abnormal level and at two normal sites (above and below the abnormal level). Surface electrodes were placed over the erector spinae muscles adjacent to each intramuscular electrode site. Electromyography signals were recorded during initial prone resting, three maximal voluntary isometric contractions (MVIC), and a second prone resting. The area under the curve for a 2-second period was analyzed for each condition, and values were normalized and reported as a percentage of MVIC. Data were analyzed using a 2-factor repeated-measures analysis of variance. RESULTS Twenty-five participants with mean (SD) thoracic pain of 3.3 (1.9) on a 0 to 10 visual analog pain scale completed the study protocol. There were no statistically significant differences in normalized resting activity between the three intramuscular sites (P=.25) or between the three surface sites (P=.33). Substantial variability in normalized resting activity at each of the three intramuscular sites was evident (mean [SD] percent of MVIC: abnormal 7.83 [8.76]; normal 9.47 [8.45], 6.65 [7.39]). No statistically significant differences existed in the intramuscular EMG values between the two resting baseline periods (P=.10). CONCLUSION The lack of statistically significant differences between EMG activity at the abnormal and normal paraspinal sites suggests that factors other than muscle activity are responsible for the apparent abnormality of these tissues to palpation. Investigation of these regions for increased tissue fluid and inflammatory mediators is recommended.