The serratus anterior is a muscle located along the side of the chest wall, positioned beneath the scapula (shoulder blade). It plays a role in arm and shoulder movements.
Anatomy and Location
The serratus anterior is a large, fan-shaped muscle that originates from the outer surfaces of the first eight or nine ribs. From there, it wraps around the side of the rib cage, passing underneath the scapula. The muscle then inserts along the entire length of the medial border of the scapula, from its superior to its inferior angle.
Its distinctive appearance, with finger-like projections connecting to the ribs, gives the muscle its name; “serratus” comes from the Latin word “serrare,” meaning “to saw,” referring to its serrated or saw-toothed edge. This wide attachment allows it to influence scapular movement.
Primary Actions
The serratus anterior performs two main actions that are fundamental to shoulder and arm function. One of its primary roles is scapular protraction, which involves pulling the scapula forward and around the rib cage. This movement is evident during pushing actions, such as when extending the arm to throw a punch, which is why the serratus anterior is sometimes referred to as the “boxer’s muscle.”
The muscle allows the shoulder blade to glide smoothly along the chest wall, enabling the arm to reach forward. Beyond protraction, the serratus anterior also plays a significant role in the upward rotation of the scapula. This action occurs with other muscles, like the trapezius, and is necessary for raising the arm overhead beyond 90 degrees. The coordinated upward rotation of the scapula helps to position the shoulder joint optimally for full arm elevation.
Role in Scapular Stability
The serratus anterior contributes to scapular stability by holding it firmly against the thoracic wall. This function helps ensure the shoulder blade remains flat against the back, preventing it from lifting away during arm movements. The stability provided by this muscle is important for efficient force transfer from the torso to the arm.
It works with other muscles to maintain proper shoulder girdle alignment, helping reduce stress on the shoulder joint.
Common Issues Related to Dysfunction
When the serratus anterior does not function as intended, it can lead to serratus anterior dysfunction. A common manifestation of this dysfunction is a “winged scapula,” where the medial border of the shoulder blade visibly protrudes or lifts away from the rib cage. This occurs because the muscle cannot keep the scapula pressed flat against the chest wall.
A winged scapula can impact arm movement, potentially leading to reduced strength and discomfort in the shoulder. Causes of serratus anterior dysfunction often include damage or weakness of the long thoracic nerve, which solely innervates this muscle. Injury to this nerve can result from trauma, repetitive strain, or viral infections.