The trapezius muscle is a large, superficial muscle that covers a significant portion of the back, extending from the base of the skull down to the middle of the back and out to the shoulder. This broad, flat muscle is responsible for complex movements and stabilization of the shoulder blade, requiring a steady and robust blood supply to function correctly. Understanding the specific arteries that deliver oxygen and nutrients to this muscle is fundamental to comprehending its anatomy.
Anatomy and Function of the Trapezius Muscle
The trapezius muscle, when viewed bilaterally, forms a kite or trapezoid shape, a characteristic that gives the muscle its name. It originates from the skull and the vertebrae of the neck and thoracic spine, extending laterally to attach to the clavicle, acromion, and spine of the scapula. This extensive span is divided into three distinct functional regions: the upper, middle, and lower fibers.
The upper or descending fibers are responsible for elevating the scapula, which is the action commonly known as shrugging the shoulders. The middle or transverse fibers primarily retract the scapula, pulling the shoulder blades back toward the spine. Finally, the lower or ascending fibers work to depress the scapula, pulling the shoulder blade downward. These coordinated actions allow for arm movement and contribute to maintaining posture.
The Direct Arterial Supply
The primary vessel responsible for the deep nourishment of the trapezius muscle is the Dorsal Scapular Artery (DSA). This major artery is distributed along the medial border of the scapula, running deep to the muscle tissue it serves. It provides numerous branches that penetrate the trapezius, particularly supplying the middle and lower portions of the muscle.
Anatomical variations exist regarding the DSA’s origin. In many cases, the Transverse Cervical Artery (TCA) arises and then splits into a superficial branch and a deep branch, with the deep branch becoming the Dorsal Scapular Artery. The superficial branch of the TCA also contributes to the blood supply of the middle fibers of the trapezius as it travels across the posterior triangle of the neck.
However, the Dorsal Scapular Artery frequently exists as its own separate vessel, arising directly from a different source. When this occurs, the TCA still gives off a superficial branch that supplies the trapezius, but the dominant deep supply is directly from the standalone DSA. The Dorsal Scapular Artery is consistently the main source of blood for the deep surface of the large, lower two-thirds of the trapezius.
Vascular Origin and Supplemental Contributions
The main vascular supply to the trapezius, the Transverse Cervical Artery, begins its journey from the Subclavian Artery. Specifically, the TCA is typically a branch of the Thyrocervical Trunk, which is a short trunk that immediately branches off the first part of the Subclavian Artery in the root of the neck. This establishes the connection to the muscle’s primary feeder vessel.
When the Dorsal Scapular Artery arises as an independent vessel, it most often branches directly from the second or third part of the Subclavian Artery itself. This variation means the dominant supply can originate from two different points along the Subclavian Artery’s pathway, either via the Thyrocervical Trunk or directly.
Beyond the TCA/DSA system, the trapezius receives supplemental contributions from several other arteries. The superior, or descending, portion of the muscle, located highest near the skull, receives branches from the Occipital Artery. This artery is a branch of the External Carotid Artery, providing a supply route separate from the subclavian system. Furthermore, the deepest parts of the lower trapezius receive minor contributions from branches of the Posterior Intercostal Arteries, which arise from the aorta and run along the ribs.