Spontaneous Needle Electromyographic Activity in Myofascial Trigger Points in the Infraspinatus Muscle: A Blinded Assessment

Abstract

Objective: Myofascial pain syndromes associated with trigger points [TrPs] are an established clinical entity but the structural and functional abnormalities of TrPs are not well under stood. The aim of the study was to conduct a blinded electromyographic investigation of TrPs.

Methods: Nineteen young subjects with chronic shoulder and arm pain, who had a TrP [i.e., a tender point with referred pain, producing at least some of the pain complaint] in the infraspinatus muscle, were examined. This point and a nontender control point in the same muscle were code-marked, in order to blind the examiner. Around both points 20 concentric needle electromyographic [EMG] recordings were obtained at rest.

Results: More subjects had spontaneous EMG activity at the TrPs than at the control point. The EMG activity was interpreted as end-plate noise or spikes or both. The TrP Root Mean Square amplitudes were significantly higher than at the control points.

Conclusion: Our investigation has demonstrated the presence of spontaneous EMG activity in myofascial TrPs, probably reflecting end-plate activity.

KEYWORDS:

• Myofascial pain
• trigger points
• spontaneous needle electromyography
• blinded comparison
• motor end-plates