The lower subscapular nerve arises from the posterior cord (C5-C6) and supplies the lower subscapularis and teres major. It is the larger of the two subscapular nerves and its teres major innervation distinguishes it from the upper subscapular nerve.
| Origin | Posterior cord of the brachial plexus (C5, C6) |
|---|---|
| Course | Descends in the axilla lateral to the subscapular vessels and the thoracodorsal nerve, giving branches to the lower subscapularis and ending in teres major |
| Motor |
Lower subscapular nerve injury weakens internal rotation and shoulder adduction (teres major). Combined upper and lower subscapular palsy denervates subscapularis and teres major completely. On EMG, denervation of teres major, subscapularis and latissimus dorsi together with deltoid and radial muscles indicates a posterior cord lesion rather than an isolated axillary or radial nerve injury. The nerve is at risk during extensive axillary dissection and subscapularis release in shoulder arthroplasty.
Weakness of internal rotation and shoulder adduction from teres major denervation, occurring in posterior cord injuries or during extensive axillary dissection for cancer surgery.
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