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Serratus anterior muscle

The serratus anterior is a large, flat, fan-shaped muscle located on the lateral thoracic wall. It originates from the outer surfaces of the first to ninth ribs and inserts along the anterior (costal) surface of the medial border of the scapula, extending from the superior to the inferior angle.

It is divided into three parts:

  • Superior part: from the first and second ribs → attaches to the superior angle of scapula

  • Intermediate part: from the 2nd–4th ribs → attaches along the medial border

  • Inferior part: from the 5th–9th ribs → attaches to the inferior angle of scapula

Functionally, the serratus anterior plays a key role in scapular protraction (pushing, punching) and upward rotation of the scapula during overhead movements. It stabilizes the scapula against the thoracic wall, enabling efficient action of the rotator cuff and deltoid. Paralysis of this muscle due to long thoracic nerve injury produces the classic winged scapula deformity.

Synonyms

  • Musculus serratus anterior

  • Boxer's muscle

  • Lateral thoracic wall stabilizer

Function

  • Protracts the scapula (moves it anteriorly around thoracic wall, as in pushing or punching)

  • Upward rotation of scapula (critical for raising the arm overhead)

  • Stabilizes the scapula against the thoracic wall during limb movements

  • Assists in forced inspiration by elevating ribs when shoulder girdle is fixed

Nerve Supply

  • Long thoracic nerve (C5–C7), a branch of the brachial plexus

Arterial Supply

  • Lateral thoracic artery (branch of axillary artery)

  • Superior thoracic artery (branch of axillary artery)

  • Contributions from thoracodorsal and intercostal arteries

Venous Drainage

  • Lateral thoracic vein → axillary vein

  • Intercostal veins → azygos/hemiazygos system

MRI Appearance

T1-weighted images:

  • Appears as intermediate signal muscle on the lateral thoracic wall

  • Fat planes between slips and ribs are hyperintense

T2-weighted images:

  • Normal muscle: intermediate-to-low signal

  • Muscle edema (denervation, trauma, overuse) appears bright hyperintense

STIR:

  • Fat suppression highlights muscle edema, inflammation, or strain

  • Sensitive for detecting denervation changes from long thoracic nerve injury

T1 Post-Gadolinium (Gd-enhanced MRI):

  • Normal muscle shows mild homogeneous enhancement

  • Abnormal enhancement in myositis, tumors, or inflammatory lesions

  • Useful in evaluating post-traumatic changes and nerve injury sequelae

MRI Non-Contrast 3D Imaging:

  • Provides multiplanar view of serratus slips and their scapular attachment

  • Useful for surgical planning in chest wall reconstruction or scapular stabilization procedures

CT Appearance

Non-contrast CT:

  • Serratus anterior visible as a thin, layered soft tissue density along the chest wall

  • Detects atrophy, fatty replacement, calcification, or traumatic injury

CT Post-Contrast:

  • Enhances visualization of inflammatory, neoplastic, or vascular lesions involving the serratus anterior

  • Helpful in mapping muscle boundaries in oncologic chest wall surgery

  • 3D reconstructions useful in trauma and surgical planning

MRI images

Serratus anterior muscle mri axial image

MRI image

Serratus Anterior Muscle anatomy MRI axial image -img-00000-00000

CT images

Serratus Anterior Muscle anatomy CT coronal image -img-00000-00000

MRI image

Serratus anterior muscle axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

CT image

Serratus anterior muscle CT axial image-img-00000-00000