All of the following muscles form part of the rotator cuff EXCEPT:

Explanation

## Rotator Cuff Anatomy **Key Point:** The rotator cuff consists of four muscles that stabilize the glenohumeral joint: supraspinatus, infraspinatus, teres minor, and subscapularis. These muscles originate from the scapula and insert on the proximal humerus. ### Rotator Cuff Muscles | Muscle | Origin | Insertion | Innervation | Primary Action | |--------|--------|-----------|-------------|----------------| | Supraspinatus | Supraspinous fossa | Greater tubercle (superior facet) | Suprascapular nerve | Initiate abduction (0–15°) | | Infraspinatus | Infraspinous fossa | Greater tubercle (middle facet) | Suprascapular nerve | External rotation | | Teres minor | Lateral border of scapula | Greater tubercle (inferior facet) | Axillary nerve | External rotation | | Subscapularis | Subscapular fossa | Lesser tubercle | Upper/lower subscapular nerves | Internal rotation | ### Why Pectoralis Major Is NOT Part of the Rotator Cuff **High-Yield:** Pectoralis major is a **prime mover** of the shoulder, not a stabilizer. It originates from the anterior chest wall (clavicle, sternum, rectus sheath) and inserts on the intertubercular groove of the humerus. Its primary actions are adduction, flexion, and internal rotation — functions of movement, not dynamic stabilization. **Clinical Pearl:** The rotator cuff's role is to maintain the humeral head centered in the shallow glenoid fossa during movement. Pectoralis major, being a large superficial muscle, contributes to power but not to the fine stabilization that characterizes rotator cuff function. **Mnemonic:** **SITS** — Supraspinatus, Infraspinatus, Teres minor, Subscapularis. Pectoralis major is not in this acronym and is not part of the cuff.