CHRONIC PAIN AFTER SOFT-TISSUE INJURY OF THE CERVICAL-SPINE - TRAPEZIUS MUSCLE BLOOD-FLOW AND ELECTROMYOGRAPHY AT STATIC LOADS AND FATIGUE

Microcirculation in the upper portion of the right and left trapezius muscles was measured percutaneously by laser-doppler fIowmetry (LDF) d uring two 10-min-long series of alternating 1-min periods of static co ntraction and rest determined electromyographically (EMG). Twenty-five patients with pain persisting after a soft-tissue injury of the neck were studied. Pain assessments by using visual analogue scales and dra wings showed 13 patients with predominantly unilateral and 12 with bil ateral neck-shoulder pain, in some cases with arm pain and numbness. M ean age was 41 (23-58) and 39 (22-54) years and a female/male ratio 8: 5 and 10:2, respectively. Stepwise increased contraction was induced b y keeping straight arms at 30 degrees, 60 degrees, 90 degrees and 135 degrees of elevation, and repeated with a 1 kg (women) or 2 kg (men) h and loads. Signal processing was done on-line by using a 386SX compute r. LDF and EMG values were normalized. Spectral shift of EMG mean powe r frequency (MPF) for fatigue was analyzed. Muscle blood flow on the ' 'normal'' side in the unilateral pain group showed an ordinary increas e at increased angle of arm elevation, shoulder torque and EMG amplitu de. On the painful side, during increased muscle tension and fatigue, the ability to increase blood now appeared to be impaired, and there w as no consistent increase in either side of the bilateral pain group. EMG amplitude showed a significant positive correlation to the angle o f arm elevation and shoulder torque. The rms-EMG (root mean squared EM G) increase was lower in the painful side at high force contraction (n on-normalized data). MPF showed 8 significant fall at increasing torqu e, and the endurance time was reduced. The results suggest a disturbed regulation of the microcirculation of the upper trapezius muscle. Chr onic trapezius myalgia may be a prominent and important feature for ma intenance of this common pain syndrome.