The serratus anterior muscle, often nicknamed the “boxer’s muscle” for its role in punching motions, is a large, fan-shaped muscle on the lateral chest wall. It is situated deep to the scapula, or shoulder blade, and the pectoral muscles, lying directly on the outside of the rib cage.
Anatomy and Function of the Serratus Anterior
The serratus anterior originates from the outer surfaces of the first eight or nine ribs, wrapping around the side of the chest. From there, its distinct slips of muscle tissue course backward to insert along the entire anterior length of the scapula’s medial border. This attachment pattern is responsible for the muscle’s saw-toothed appearance, from which its name is derived.
The primary action of the serratus anterior is to protract the scapula, which means pulling the shoulder blade forward and around the rib cage, such as when pushing an object or throwing a punch. It also acts to stabilize the scapula by holding it firmly against the thoracic wall during movement. Furthermore, the muscle works in coordination with the trapezius to rotate the scapula upward, allowing the arm to be raised above the shoulder level.
The neurological control for this muscle is provided by the Long Thoracic Nerve, which arises from spinal nerve roots C5, C6, and C7. This nerve travels down the chest wall, running directly on the superficial surface of the serratus anterior muscle. Injury to this nerve can cause muscle paralysis, resulting in a distinct clinical presentation.
The Primary Arterial Source
The main blood supply to the serratus anterior comes from the Lateral Thoracic Artery. This artery is a direct branch arising from the Axillary Artery. The Lateral Thoracic Artery descends along the lower edge of the pectoralis minor muscle, distributing branches directly into the serratus anterior.
While the Lateral Thoracic Artery is the principal source, the muscle also receives supplementary contributions from two other arteries. The upper portion is supplied by branches of the Superior Thoracic Artery. This vessel supplies blood to the superior aspect of the chest wall and the upper slips of the serratus anterior.
The lower portion of the muscle receives blood from the Thoracodorsal Artery, which descends with the Long Thoracic Nerve. The Thoracodorsal Artery itself is a terminal branch of the Subscapular Artery, another large branch stemming from the Axillary Artery. This arrangement means that the serratus anterior has a robust and redundant vascular network, all originating from the main arterial trunk of the axilla.
This multi-source blood supply is partitioned geographically, with the Lateral Thoracic Artery supplying the central portion, the Superior Thoracic Artery supplying the upper slips, and the Thoracodorsal Artery supplying the lower slips. The Thoracodorsal Artery is especially important for the inferior part of the muscle, providing a reliable pedicle that is often utilized in surgical procedures.
Clinical Importance of the Blood Supply
Knowledge of the serratus anterior’s blood supply is important in clinical medicine and surgery. The muscle’s proximity to the Long Thoracic Nerve means that trauma or surgical procedures in the armpit region can risk damage to both the nerve and adjacent blood vessels. Damage to the nerve results in paralysis and the inability to hold the scapula against the chest, causing the condition known as “winged scapula.”
If the Lateral Thoracic Artery or its branches are compromised, the resulting reduction in blood flow can lead to muscle ischemia, which restricts blood supply. While nerve injury is the more common cause of serratus anterior dysfunction, arterial damage can impair muscle function and delay recovery.
The muscle is highly valued in reconstructive surgery, particularly as a pedicled flap for covering defects elsewhere in the body. The lower part of the muscle, supplied by the Thoracodorsal Artery, can be harvested along with its intact vascular pedicle and transplanted to reconstruct complex defects, such as those in the hand or breast.
Surgeons rely on the predictable path of the Thoracodorsal Artery to ensure the transplanted tissue remains viable by maintaining its blood supply. Preserving the integrity of this vascular axis is a primary consideration during procedures like axillary lymph node dissection, where the artery and nerve run in close association.