A Variant of the Deltoid Muscle and Its Clinical Implications: A Cadaveric Study

Abstract

Background: The deltoid is the muscle that forms the rounded contour of the shoulder. Anatomically, it seems to be made up of three different sets of fibers. The three anatomical portions in which the deltoid muscle are typically divided into the anterior (clavicular), the mean (acromial), and the posterior (spinal). Different variations of the deltoid muscle have been described in the literature. The analysis and knowledge of these anomalies are essential for surgeons and anatomists. Methods: A total of 21 specimens (12 women and 9 men) were used with a 10% formaldehyde solution. All specimens were dissected bilaterally (the classical dissection methodology was used). Results: In one corpse, an additional bilateral belly of the deltoid muscle was found. It was observed that this additional muscular belly was related to the fascial tissue of the deltoid muscle and its muscle fibers take origin from the middle third of the inferomedial bands of infraspinatus fascia. In addition, the belly attaches to the posterior belly of the deltoid muscle. The deltoid muscle and the additional belly were innervated by the axillar nerve, which is a lateral terminal bouquet of the posterior fascicle of the brachial plexus. Conclusions: This new variation of the deltoid muscle must be considered by surgeons, as well as abnormal conditions in terms of compartment syndrome involving the shoulder. Therefore, consideration of this variant is necessary for the correct diagnosis and treatment of trauma or other shoulder pathology that may be refractory to standard treatments.