Structure and location
The serratus anterior muscle belongs to the group of superficial chest muscles, which embryologically originate from the muscles of the upper extremity.
- Origin: originates by 8–9 muscular slips from the 1st to 9th ribs. The muscle reaches its maximum development in the area of the inferior angle of the scapula.
- Insertion: the muscle bundles attach to the anterior surface of the medial border and the inferior angle of the scapula.
Function
The muscle provides movement and fixation of the scapula:
- Pulls the scapula anteriorly and laterally.
- Produces lateral and upward rotation of the scapula, which is necessary for elevating the arm above the horizontal plane.
- Fixes the scapula to the thoracic wall.
- The lower bundles of the muscle function as a powerful inspiratory stabilizer.
Blood supply and innervation
- Innervation: supplied by the long thoracic nerve — n. thoracicus longus (C5–C7 of the brachial plexus).
- Blood supply:
- Thoracodorsal artery (a. thoracodorsalis).
- Lateral thoracic artery (a. thoracica lateralis).
- Superior thoracic artery (a. thoracica superior).
- Pectoral branches of the thoracoacromial artery (rr. pectorales a. thoracoacromialis).
- Intercostal arteries (aa. intercostales).
Topography and adjacent structures
The muscle participates in the formation of several important topographical regions:
- On the lateral chest wall: the long thoracic nerve (n. thoracicus longus) runs along the superficial surface of the serratus anterior muscle. It is located 1.5–2.0 cm posterior to the lateral thoracic vessels (a. et v. thoracicae laterales), which run along the lateral border of the pectoralis minor muscle.
- In the subclavian region: on a sagittal section, the serratus anterior muscle follows sequentially after the subclavius, pectoralis major, and pectoralis minor muscles.
- In the axillary fossa: the first part of the axillary artery (a. axillaris) lies on the upper slips of the m. serratus anterior.
- Subscapular space: the serratus anterior muscle, covered by the deep cervical fascia (thoracic fascia, fascia thoracica), forms the anterior wall of the subscapular fascial space; the posterior wall is formed by the subscapularis muscle.
- Medial border of the scapula: the dorsal scapular artery (a. scapularis dorsalis) runs between the serratus anterior and rhomboid muscles.
Clinical significance
Neurological diagnosis In case of isolated lesion of the serratus anterior muscle, pathology of the long thoracic nerve should be ruled out. The following tests are used to assess function:
- Wall push-up test: a positive result is indicated by the medial border of the scapula protruding away from the thoracic wall, forming a pathological "winged scapula".
- Arm abduction test: abduction of the shoulder in the plane of the scapula at an angle of 120–130 degrees is assessed. In case of weakness, the patient cannot resist the examiner's force.
The muscle is included in the expanded needle electromyography (EMG) protocol for differential diagnosis and to rule out lesions of the brachial plexus trunks.
Thoracic surgery During posterolateral thoracotomy, the patient lies in the lateral position (or prone), and the incision curves around the scapular angle, ending at the midaxillary or anterior axillary line. In the lower half of the surgical approach, the latissimus dorsi and serratus anterior muscles are divided layer by layer.
Class and exam questions
Which nerve innervates the serratus anterior muscle and how is it positioned relative to neighboring structures?
The muscle is innervated by the long thoracic nerve (n. thoracicus longus). It runs along the superficial surface of the muscle 1.5–2.0 cm posterior to the lateral thoracic vessels.
How to test m. serratus anterior function during a physical examination?
The wall push-up test is performed. If the muscle fails to perform its fixation function, the medial border of the scapula lifts off the chest wall (causing a "winged scapula"). Resistance strength during shoulder abduction to 120–130 degrees is also tested.
What fascial space does this muscle help form?
The serratus anterior muscle, covered by the thoracic fascia (fascia thoracica), forms the anterior wall of the subscapular fascial space. The subscapularis muscle serves as the posterior wall of this space.
What movements of the scapula are provided by the serratus anterior muscle?
It pulls the scapula anteriorly and laterally, and also rotates it laterally and upward. This rotation is essential for a person to be able to raise the arm above the horizontal level.
What else to study on this topic
- Long thoracic nerve (n. thoracicus longus)
- Axillary artery (a. axillaris)
- Subscapular fascial space
- Brachial plexus (plexus brachialis)
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