The upper slips of serratus anterior, arising from ribs 1-6, are the portion that contributes to scapular upward rotation alongside the lower slips. These upper slips are more horizontal and contribute primarily to scapular protraction, while the lower slips (ribs 7-9) are the main upward rotators.
| Origin | Outer surfaces of ribs 1-6 (upper slips) |
|---|---|
| Insertion | Costal surface of medial scapular border — upper portion |
| Nerve Supply | Long thoracic nerve (C5, C6, C7) |
| Blood Supply | Lateral thoracic artery |
| Actions | Protracts the scapula; Assists in upward rotation — rotates the glenoid upward for shoulder elevation |
|---|
Long thoracic nerve palsy from serratus weakness produces medial scapular winging that increases on arm elevation. EMG sampling of the upper versus lower serratus slips helps localise injury level within the long thoracic nerve. The upper serratus slips are less visible on winging assessment than the lower slips, making selective upper slip weakness easy to miss.
The upper serratus slips are palpable along the anterolateral rib cage during resisted shoulder protraction, lateral to the pectoralis major.
Weakness of the upper serratus anterior slips from partial long thoracic nerve injury producing subtle protraction weakness without the dramatic winging seen with complete lower slip involvement.
