Anatomy of the deltoid muscle trigger points.

Myofascial Pain Syndrome (MPS) is regarded as an extremely common clinical disorder, but is not fully understood. Shoulder pain has a lifetime prevalence of up to 66.7% in the general population, and pain due to Myofascial Trigger Points (MTPs) located in the deltoid muscle is fairly common. Analyses of the correlations between innervation patterns and trigger point locations have been successful in other muscular groups. The objective of this study was to provide a mathematical analysis of the entry points of the axillary nerve into the deltoid muscle and correlate them with the described areas of myofascial pain. Ten cadavers were carefully dissected to measure a series of parameters in each deltoid muscle. The entry points of the axillary nerve into the deltoid muscle were placed in a cartesian graph created by dividing the deltoid muscle into 4-quadrants. Statistical analysis was carried out on the number of points in each quadrant. Quadrant 1 had the largest number of axillary nerve entry sites, with a mean of 6.85 sites (63%), followed by quadrant 3 with 2.75 sites (25%), quadrant 2 with 1.15 sites (10%), and quadrant 4 with 0.25 sites (2%). In accordance with the clinical literature, the branches of the axillary nerve in the deltoid muscle corresponded to the described areas of the MTPs. Anatomical correlations between MTPs may be useful tools for gaining a better understanding of the physiopathology of these disorders and providing a basis for their treatment.