A man can not able to do abduction &internal rotation of the arm. Which of the following muscle is responsible for both movement?
**Core Concept**
The question tests the understanding of the motor functions of the shoulder joint, specifically the muscles responsible for abduction and internal rotation of the arm. The deltoid and rotator cuff muscles play key roles in shoulder movement.
**Why the Correct Answer is Right**
Internal rotation of the arm is primarily facilitated by the latissimus dorsi muscle, but in the context of shoulder joint movement, the supraspinatus muscle, a part of the rotator cuff, also helps in internal rotation. Additionally, the deltoid muscle is responsible for abduction of the arm. The supraspinatus muscle is particularly crucial for both abduction and internal rotation of the arm, especially when the arm is at the side or in mid-range abduction.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the biceps brachii muscle is primarily responsible for elbow flexion and forearm supination, not abduction or internal rotation of the arm.
* **Option B:** This option is incorrect because the trapezius muscle assists in scapular elevation and downward rotation, but it does not play a significant role in the abduction and internal rotation of the arm.
* **Option C:** This option is incorrect because the pectoralis major muscle is involved in shoulder flexion, adduction, and medial rotation, but not abduction and internal rotation.
**Clinical Pearl / High-Yield Fact**
The rotator cuff muscles (supraspinatus, infraspinatus, teres minor, and subscapularis) are crucial for shoulder stability and function. Damage to these muscles can lead to shoulder impingement and rotator cuff tears.
**Correct Answer: D. Supraspinatus muscle is responsible for both movement.**