The serratus anterior is a broad, saw-toothed muscle wrapping around the lateral chest wall and connecting eight ribs to the full length of the medial scapular border. It is the essential partner to the trapezius in rotating the glenoid upward during arm elevation, and its failure produces medial scapular winging. Without adequate serratus function, full overhead range of motion cannot be achieved because the glenoid cannot rotate to clear the acromion.
| Origin | Outer surfaces of ribs 1 through 8 via finger-like digitations |
|---|---|
| Insertion | Entire costal surface of the medial scapular border |
| Nerve Supply | Long thoracic nerve (C5, C6, C7) |
| Blood Supply | Lateral thoracic artery |
| Actions | Protraction of the scapula; Upward rotation of the glenoid during arm elevation; Holds the medial scapular border flat against the rib cage |
|---|
It protracts the scapula and rotates the glenoid upward during arm raising, working as half of the scapular force couple with the lower trapezius. When this force couple is disrupted, compensatory impingement patterns almost always follow.
Long thoracic nerve palsy from direct axillary trauma, viral neuritis, or heavy backpack use paralyses the serratus and produces classic medial scapular winging that becomes most pronounced during a wall push-up. This pattern differs from trapezius winging, which lifts the superior angle more than the inferior. Serratus weakness is also a consistent finding in shoulder impingement because the reduced upward rotation narrows the subacromial outlet.
The digitations of the serratus anterior are visible and palpable on the lateral rib cage between the anterior axillary line and the latissimus dorsi border, particularly in lean individuals performing a forward push against resistance.
Nerve injury from trauma, traction, or viral illness paralyses the serratus anterior and produces medial scapular winging that worsens with arm elevation and the wall push-up test.
Acute tearing of the digitations from a sudden forceful pushing or reaching movement, producing sharp lateral chest pain that worsens with both breathing and shoulder movement.
