The spatial relationship between myofascial trigger points and the innervation zone in upper trapezius

Barbero, Marco and Macmillan, Fiona and Coutts, Fiona and Cescon, Corrado and Merletti, Roberto and Gatti, Roberto and Leggero, Vittorio and Cifoletti, Damiana (2012) The spatial relationship between myofascial trigger points and the innervation zone in upper trapezius. In: Proc. of the XIX Congress of the International Society of Electrophysiology and Kinesiology, July 19-21, Brisbane, Australia.

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INTRODUCTION: Myofascial trigger points (MTrP) have been defined as highly localized and hyperirritable spots located in a palpable taut band of skeletal muscles. Although their aetiology is not clearly understood, electrophysiological studies indicated that an abnormal electrical activity around the innervation zone (IZ) is more prevalent in the MTrP region. This phenomenon has been described as endplate noise due to an excessive release of acetylcholine and, together with nerve fiber sensitization, constitutes the basis for MTrPs pathophysiology. Thus the hyperirritable spot defined as the sensory component of MTrP is described as overlapping the IZ. AIM: The purpose of this work is to describe the spatial relationship between MTrPs and IZs in the upper trapezius. METHODS: Twenty-four patients with neck pain and MTrPs (21 active MTrP and 3 latent MTrPs) together with 24 healthy subjects with latent MTrPs were recruited through the San Raffaele Scientific institute in Milan. A physiotherapist examined the enrolled subject’s trapezius to confirm the presence of MTrPs and to mark their exact location using a special stamp (a circle of 1cm² with a dot in the centre). Subsequently another operator traced a reference system on each subject’s mid-trapezius to measure the MTrP location. sEMG signals were recorded during an isometric contraction at 20% of the maximal voluntary contraction (MVC) using a 2D electrode array (13 rows x 5 columns) placed on mid-trapezius. Both the MTrP and IZ locations were measured using the same coordinate system. Student t-test was used to evaluate if the distance between IZs and MTrPs was significantly different from zero and to evaluate differences between active and latent MTrPs. RESULTS: According to our coordinate system 45 MTrPs were included in the 3rd quadrant (bottom left portion of the coordinate axis) except 3 included in 2nd quadrant (top left). IZs were approximately located to the middle of upper trapezius fibers, midway between C7 and the acromial angle. The mean distance between MTrP and IZ was about 10 mm for both active and passive MTrPs (significantly different from zero; P<0.001) with IZ located more laterally with respect to the MTrPs. No significant difference was observed between active and latent MTrPs (P=0.6). CONCLUSION: A clear overlapping between MTrPs and IZ was not observed, however both active and latent MTrPs were located medially to the IZs, and their mean distance was about 10 mm. Interestingly MTrPs in upper trapezius seem to be grouped in a well defined area. Our findings raise questions on the nature of MTrP sensory component.

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