The serratus anterior muscle is a muscle that originates from the upper eight or nine ribs and inserts onto the scapula (shoulder blade). It is a thin, broad muscle that wraps around the side of the ribcage and attaches to the scapula.
Structure
- Origin: The serratus anterior muscle originates from the upper eight or nine ribs, specifically from the external surfaces of the ribs at the level of the intercostal spaces.
- Insertion: The muscle inserts onto the scapula, specifically onto the vertebral border and the superior border of the scapula.
- Innervation: The serratus anterior muscle is innervated by the long thoracic nerve, a branch of the brachial plexus.
Location
The serratus anterior muscle is located on the sides of the ribcage, between the ribcage and the scapula (shoulder blade). It is a thin, broad muscle that wraps around the side of the ribcage and attaches to the scapula.
The muscle originates from the upper eight or nine ribs, specifically from the external surfaces of the ribs at the level of the intercostal spaces. It inserts onto the scapula, specifically onto the vertebral border and the superior border of the scapula. The muscle is innervated by the long thoracic nerve, a branch of the brachial plexus.
The serratus anterior muscle is visible when the arms are raised overhead or when the scapula protracts, as the muscle’s contraction causes the scapula to move outward and upward. It is often referred to as the “boxer’s muscle” because it is visible when the arms are raised in a boxing stance.
Function
The serratus anterior muscle has several functions, including:
- Protraction of the scapula: The serratus anterior muscle is responsible for protracting the scapula, which means it moves the scapula forward and outward away from the spine. This is important in movements such as reaching and lifting.
- Upward rotation of the scapula: The serratus anterior muscle also rotates the scapula upward, which helps to lift the arm overhead.
- Stabilization of the scapula: The serratus anterior muscle plays a role in stabilizing the scapula during shoulder movements, such as lifting and reaching. It helps to keep the scapula in proper position and prevent it from moving excessively.
- Respiration: The serratus anterior muscle is also involved in respiration, as it helps to elevate the ribcage during inhalation.
Clinical significance
Winged scapula
Damage to the serratus anterior muscle or its innervating nerve can lead to a condition called “winged scapula,” in which the scapula protrudes outward and cannot be properly stabilized during shoulder movements. This can result in weakness and difficulty with activities such as lifting and reaching overhead.
- Symptoms: Symptoms of winged scapula may include visible protrusion of the scapula, weakness in the shoulder and arm, difficulty lifting and reaching overhead, and pain in the shoulder and upper back.
- Causes: Causes of winged scapula can include injury to the serratus anterior muscle or its innervating nerve, as well as muscle atrophy or weakness due to disuse or aging.
- Diagnosis: Winged scapula is typically diagnosed based on a physical examination, which may include testing for scapular protraction and movement. X-rays or other imaging studies may also be used to rule out other underlying conditions.
- Treatment: Treatment for winged scapula may include physical therapy to strengthen the serratus anterior muscle and improve scapular stability, as well as other supportive measures such as taping or bracing to help hold the scapula in proper position. In severe cases, surgery may be necessary to repair or reconstruct the muscle or nerve.
