Which rotator cuff muscle is innervated by the suprascapular nerve and is responsible for initiating abduction of the shoulder?

Explanation

## Supraspinatus: Anatomy and Function **Key Point:** The supraspinatus is the only rotator cuff muscle that initiates shoulder abduction; the deltoid continues the movement beyond 15–20 degrees. **High-Yield:** Supraspinatus is innervated by the **suprascapular nerve** (branch of the superior trunk of the brachial plexus, C5–C6), which travels through the suprascapular notch. ### Functional Anatomy - **Origin:** Supraspinous fossa of the scapula - **Insertion:** Superior facet of the greater tuberosity of the humerus - **Action:** Initiates shoulder abduction (0–15 degrees); stabilizes the humeral head in the glenoid - **Clinical significance:** Supraspinatus tears are the most common rotator cuff injury and present with loss of active abduction ("drop arm" sign) ### Rotator Cuff Innervation Summary | Muscle | Nerve | Root | | --- | --- | --- | | Supraspinatus | Suprascapular | C5–C6 | | Infraspinatus | Suprascapular | C5–C6 | | Teres minor | Axillary | C5–C6 | | Subscapularis | Upper & lower subscapular | C5–C6 | **Mnemonic:** **SITS** = Supraspinatus, Infraspinatus, Teres minor, Subscapularis (the four rotator cuff muscles in anatomical order from superior to inferior posteriorly, plus subscapularis anteriorly).