A Novel Bipartite Trapezius Muscle Variant: Functional and Clinical Considerations

Abstract

During dissection of the posterior triangle in a human cadaver (Caucasian female, 102 years of age), we observed a novel arrangement of the trapezius muscle on the subject's left side only, where it consisted of two separate muscle masses. The trapezius muscle on the subject's right side appeared normal.Regarding the trapezius muscle on the subject's left side: The superior group of muscle fibers (sometimes referred to as the descending muscle fibers of trapezius) had normal attachments to the medial superior nuchal line of the occipital bone, ligamentum nuchae, and 7th cervical vertebra. However, the superior group of muscle fibers was completely separate from the remainder of the trapezius muscle and formed a discrete muscle mass that passed antero‐inferiorly, crossing the middle of the posterior triangle of the neck, and attached anomalously to the superior surface of the medial ½ of the clavicle. This muscle mass covered approximately 25% of the surface area of the posterior triangle. To our knowledge, this variant has not been previously described in scientific literature. The inferior part of the trapezius, consisting of middle and inferior trapezius fibers, had normal attachments to the spinous processes of the thoracic vertebrae, spine and acromion of the scapula.Since the superior group of muscle fibers of the trapezius muscle are normally involved in scapular elevation and superior rotation, variations of the bony attachment of these fibers would inevitably affect the normal function and kinematics of the shoulder girdle and upper limb on the affected side of the body. In addition to functional considerations, this anatomical variation has implications for surgical procedures in the posterior triangle of the neck.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.