Clinical precision of myofascial trigger point location in the trapezius muscle

Myofascial trigger points (TrPs) have been clinically described as discrete areas of muscle tenderness presenting in taut bands of skeletal muscle. Us ing well-defined clinical criteria, prior investigations have demonstrated interrater reliability in the diagnosis of TrPs within a given muscle. No r eports exist, however, with respect to the precision with which experienced clinicians can determine the anatomic locations of TrPs within a muscle. T his paper details a study wherein four trained clinicians achieved statisti cally significant reliability (see below) in estimating the precise locatio ns of latent TrPs in the trapezius muscle of volunteer subjects (n = 20). T o do so, the clinicians trained extensively together prior to the study. Th e precise anatomic location of each subject's primary TrP was measured in a blinded fashion using a 3 dimensional (3-D) camera system. Use of this mea surement system permitted the anatomic co-ordinates of each TrP to be locat ed without providing feedback to subsequent clinicians. The clinicians each used a pressure algometer along with patient feedback to document the sens itivity of each suspected TrP site, however unlike routine clinical practic e, the algometry was performed with a double-blinded approach hence the res ults were only examined post-hoc. At the time of data collection (algometry readings unknown), 16 of the 20 subjects were judged to present with a lat ent TrP. Subsequently, when subjected to a criterion pressure threshold val ue of <3.0 kg.cm, 12 of these TrPs were classified as being clinically sens itive. To assess the 3-D measurement precision, and the reliability of the TrP estimates, statistical measures of the SEM and the Generalizability coe fficient (G-coeff) were determined for all suspected TrP sites in the super ior-inferior, medial-lateral and anterior-posterior directions. The best re sults were determined by pooling the measurements of all 4 clinicians, howe ver, based upon exceeding a criterion reliability threshold of 80%, the use of just two testers was found to produce reliable results. The two-tester condition yielded a precision of 7.5, 7.6 and 6.5 mm. (SEM) with reliabilit y (G-coeff) of 0.92, 0.86 and 0.83, respectively. Given the double-blinded methodology, the use of pressure algometry was also found to demonstrate in ternal validity. The algometer responses associated with TrP estimates vari ed inversely with respect to the clinical group's reliability in identify t he TrP locations. To summarize, for the trapezius muscle, this study demons trates that two trained examiners can reliably localize latent TrPs with a precision that essentially approaches the physical dimensions of the clinic ian's own fingertips. Finally, it should be recognized that the ability to precisely document TrP location appears critical to the success of future s tudies that may be designed to investigate the etiology and pathogenesis of this commonly diagnosed clinical disorder. <(c)> 2001 International Associ ation for the Study of Pain. Published by Elsevier Science B.V. All rights reserved.