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

Explanation

## Supraspinatus: Anatomy and Function **Key Point:** The supraspinatus is the most commonly injured rotator cuff muscle and is responsible for the first 15–20° of shoulder abduction (initiating the movement). ### Innervation - **Nerve:** Suprascapular nerve (branch of superior trunk of brachial plexus, C5–C6) - **Course:** Passes through the suprascapular notch of the scapula ### Origin and Insertion - **Origin:** Supraspinous fossa of the scapula - **Insertion:** Superior facet of the greater tubercle of the humerus ### Function 1. Initiates shoulder abduction (0–15°) 2. Assists in stabilizing the humeral head in the glenoid cavity 3. Works synergistically with the deltoid (which takes over abduction after 15°) ### Clinical Significance - Most frequently torn rotator cuff muscle - Injury results in loss of initiation of abduction ("drop arm" sign) - Suprascapular nerve compression at the suprascapular notch causes infraspinatus atrophy preferentially **High-Yield:** Supraspinatus initiates abduction; deltoid completes it. This is a classic exam question. **Mnemonic:** **SITS** muscles of rotator cuff = **S**upraspinatus, **I**nfraspinatus, **T**eres minor, **S**ubscapularis. Supraspinatus is the "S" that starts abduction.