Chronic pain after soft-tissue injury of the cervical spine: trapezius muscle blood flow and electromyography at static loads and fatigue

Abstract

Microcirculation in the upper portion of the right and left trapezius muscles was measured percutaneously by laser-doppler flowmetry (LDF) during two 10-min-long series of alternating 1-min periods of static contraction 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 drawings showed 13 patients with predominantly unilateral and 12 with bilateral neck-shoulder pain, in some cases with arm pain and numbness. Mean 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 by 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) hand loads. Signal processing was done on-line by using a 386SX computer. LDF and EMG values were normalized. Spectral shift of EMG mean power frequency (MPF) for fatigue was analyzed. Muscle blood flow on the "normal" side in the unilateral pain group showed an ordinary increase at increased angle of arm elevation, shoulder torque and EMG amplitude. On the painful side, during increased muscle tension and fatigue, the ability to increase blood flow appeared to be impaired, and there was no consistent increase in either side of the bilateral pain group. EMG amplitude showed a significant positive correlation to the angle of arm elevation and shoulder torque. The rms-EMG (root mean squared EMG) increase was lower in the painful side at high force contraction (non-normalized data).(ABSTRACT TRUNCATED AT 250 WORDS)

Upper trapezius muscle activation patterns in neck–shoulder pain patients and healthy controls

“…Comparable results were also reported by Westgaard et al (2001) who did not Wnd signiWcantly increased EMG activity of the trapezius muscles in subjects with neck-shoulder pain, and Larsson et al (1994) only found a tendency towards an increase in RMS values in chronic WAD patients. In addition Holte and Westgaard (2002) found that WMSD patients were not necessarily characterised by increased muscle activity levels.…”

“…However not all studies report such clear diVerences between activity levels in pain patients and healthy controls (e.g. Larsson et al 1994).…”

Reliability of bloodflux measurements from the upper trapezius muscle during muscle contractions

“…Larsson and coworkers (Larsson et al 1999(Larsson et al , 1994 have reported lower blood fluxes in the painful muscles. It is worth noting that they applied absolute flux units in their analysis, and only normalized across experimental conditions within each individual (Larsson et al 1999(Larsson et al , 1993b.…”

“…This method has proven valid in animal studies (Stern 1975), and has been applied in humans. Larsson and coworkers have reported laser-Doppler measures of blood flux in both healthy subjects and subjects with various pain conditions (Larsson et al 1993a(Larsson et al , 1994. Their results suggested that blood flux might be inadequate relative to metabolic demands during higher-level static contractions.…”

Autonomic Regulation in Musculoskeletal Pain

“…In a series of studies, Larsson and colleagues investigated local microcirculation using laser Doppler flowmetry in patients with chronic neck pain. During static contractions, reduced microcirculation was observed in painful muscles among patients (Larsson et al 1994). In addition, a greater reduction in blood flow was associated with a higher pain intensity and mitochondrial changes in patients (Larsson et al 1990).…”