Clinical and Etiological Update of Myofascial Pain from Trigger Points

Abstract

Objectives: To review clinical literature concerning the prevalence, diagnostic criteria, and treatment of myofascial trigger points [TrPs] and to summarize a new understanding of their etiology. Findings: In three studies, the prevalence of myofascial TrPs among patients complaining of pain anywhere in the body ranged from 30% to 93%; among patients with chronic craniofacial pain, 55%; and for lumbogluteal pain, 21%. Among four studies of interrater reliability for five TrP diagnostic characteristics, untrained experienced examiners achieved unsatisfactory mean kappa values of 0.35 and 0.38, trained inexperienced examiners examiners a fai value of 0.49, and trained experience examiners a good mean kappa of 0.74. The highest mean kappa values were for spot tenderness, pain recognition, and palpable band [0.84-0.88]. A revision of previous injection technique more effectively inactivates the multiple active loci that are an essential part of a trigger point. Recent literature introduced two differing hypotheses for the basic of TrPs: 1. dysfunctional muscle spindles; 2. dysfunctional extrafusal neuromuscular junctions. Clinically, TrPs are found in the endplate zone. Electrophysiological investigations of TrPs reveals phenomena which indicate that the electrical activity of active loci arises from dysfunctional extrafusal motor endplates rather than from muscle spindles. Conclusions: Myofascial TrPs are a common cause of musculoskeletal pain. Reliable diagnostic examination requires both training and experience. Several considerations help one to decide which are the most suitable diagnostic criteria of myofascial TrPs under given circumstances. The characteristic electrical activity of myofascial TrPs most likely originates at dysfunctional endplates of extrafusal muscle fibers. This dysfunction appears to play a key role in the pathophysiology of TrPs.