## **Core Concept**
The rotator cuff is a group of muscles and their tendons that surround the shoulder joint, keeping the head of the humerus firmly within the shallow socket of the shoulder. It is composed of four muscles: supraspinatus, infraspinatus, teres minor, and subscapularis.

## **Why the Correct Answer is Right**
The muscles that form the rotator cuff are specifically the supraspinatus, infraspinatus, teres minor, and subscapularis. These muscles work together to stabilize the shoulder joint and facilitate a wide range of movements. The teres major, although located near the rotator cuff muscles and involved in shoulder movement, is not considered part of the rotator cuff.

## **Why Each Wrong Option is Incorrect**
* **Option A:** Supraspinatus - This muscle is one of the four muscles that make up the rotator cuff. It helps to stabilize the shoulder joint and is involved in abduction of the arm.
* **Option B:** Infraspinatus - This is another muscle of the rotator cuff, contributing to the stability of the shoulder joint and assisting in lateral rotation of the arm.
* **Option C:** Teres minor - This muscle is also a part of the rotator cuff. It assists in adduction and lateral rotation of the arm.
* **Option D:** Teres major - **This is the correct answer because** the teres major, while involved in movements of the shoulder (such as adduction, medial rotation, and extension), is not considered one of the muscles that form the rotator cuff.

## **Clinical Pearl / High-Yield Fact**
A useful clinical correlation to remember is that rotator cuff injuries often present with weakness in specific movements: supraspinatus injury affects arm abduction, infraspinatus and teres minor injuries affect external rotation, and subscapularis injury affects internal rotation. The teres major, not being part of the rotator cuff, injuries would present differently.

## **Correct Answer:** D. Teres major