46 - Anatomical Study of the Innervation of the Pectoralis Major Muscle and Its Correlation with Myofascial Trigger Points: Preliminary Results

Poster Board Number: 46
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Co-authors:

Gabriela Neves - graduate student, Surgery, University of São Paulo; Flavia Akamatsu - Professor, Surgery, 116.319.698-38; Flávio Hojaij - PhD, Surgery, University of São Paulo; Mauro Andrade - Professor, Surgery, University of São Paulo; Alfredo Jacomo - Head Professor, Surgery, University of São Paulo

Abstract Body :Myofascial Pain Syndrome (MPS) is a highly prevalent condition and when it involves the pectoralis major muscle, dysfunction of the shoulder biomechanics may supervene. Usually, MPS depends on the activation of Myofascial Trigger Points (MTPs) following muscle overuse.Objective: To describe the branching of the lateral and medial pectoral nerves to the pectoralis major muscle and relate it to MTPs.Methods: Five fixed cadavers were used for dissection of the right and left pectoralis major muscles to identify the nerve entry points. Muscles were divided in three major regions (superior, intermediate and inferior) then subdivided into four areas inside them to establish topographical data and facilitate clinical correlation.The number of nerve branches reaching each area was described and compared using generalized estimation equations with a matrix of interchangeable correlations between sides and quadrants, with Poisson marginal distribution and identity link function followed by Bonferroni multiple comparisons to identify differences among areas. Sides were compared made by Student’s t-test. Level of significance was adjusted to 5% (p < 0.05).Results: Areas VII, V, VIII and VI concentrated most of the pectoralis nerves entry points, in the intermediate region of the muscle. These locations correspond to the clinically described MTP. The branching pattern did not differ according to side.Conclusion: Innervation pattern of the pectoralis major muscle showed strong correlation with MTPs and may explain relevant aspects of the pathophysiology of MPS. Also, it provides useful knowledge for targeted therapeutic interventions.