Structure and Location
The serratus anterior belongs to the superficial group of chest muscles, which embryologically and functionally function as upper limb muscles.
- Origin: Arises via 8–9 muscular slips from the 1st to 9th ribs. The muscle reaches its maximum development near the inferior angle of the scapula.
- Insertion: The muscle fibers 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.
- Rotates the scapula laterally and upward, which is essential for elevating the arm above the horizontal plane.
- Fixes the scapula against the thoracic wall.
- The lower slips function as an active accessory muscle of inspiration and stabilizer.
Blood Supply and Innervation
- Innervation: Supplied by the long thoracic nerve — n. thoracicus longus (roots 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 Related Structures
The muscle contributes to several key anatomical spaces and landmarks:
- Lateral chest wall: The long thoracic nerve (n. thoracicus longus) runs along the superficial surface of the serratus anterior, located 1.5–2.0 cm posterior to the lateral thoracic vessels (a. et v. thoracicae laterales), which course along the lateral border of the pectoralis minor.
- Subclavicular region: In sagittal cross-sections, the serratus anterior lies deep to the subclavius, pectoralis major, and pectoralis minor muscles.
- Axilla: The first part of the axillary artery (a. axillaris) rests on the superior slips of the m. serratus anterior.
- Subscapular space: The serratus anterior, covered by the fascia thoracica, forms the anterior wall of the subscapular fascial space; the subscapularis muscle forms its posterior wall.
- Medial border of the scapula: The dorsal scapular artery (a. scapularis dorsalis) courses between the serratus anterior and the rhomboid muscles.
Clinical Significance
Neurological Diagnosis Isolated weakness or paralysis of the serratus anterior typically indicates injury to the long thoracic nerve. Standard clinical tests include:
- Wall push-up test: A positive test reveals the medial border and inferior angle of the scapula protruding posteriorly, producing a classic "winged scapula".
- Arm abduction test: Evaluates active abduction in the scapular plane to 120–130 degrees. With weakness, the patient cannot overcome resistance applied by the examiner.
Needle electromyography (EMG) of the serratus anterior is often included in comprehensive protocols to rule out brachial plexus trunk lesions.
Thoracic Surgery During posterolateral thoracotomy incisions, the latissimus dorsi and serratus anterior muscles are sequentially divided along the surgical access pathway tracking around the scapular angle.