Abduction of shoulder is initiated by
**Core Concept**
The abduction of the shoulder joint involves the movement of the arm away from the midline of the body, primarily facilitated by the deltoid muscle. This movement is a complex process that involves the coordination of multiple muscles and joints.
**Why the Correct Answer is Right**
The abduction of the shoulder is initiated by the supraspinatus muscle, which is one of the rotator cuff muscles. The supraspinatus muscle contracts first to stabilize the humeral head in the glenoid cavity and then assists in the initiation of abduction by rotating the humerus externally. This external rotation helps to position the arm for further abduction by the deltoid muscle. The supraspinatus muscle is innervated by the suprascapular nerve and originates from the supraspinous fossa of the scapula.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not mentioned in the context of shoulder abduction.
* **Option B:** This option is not relevant to the initiation of shoulder abduction.
* **Option C:** This option is incorrect because the deltoid muscle is responsible for the final stages of abduction, not the initiation.
**Clinical Pearl / High-Yield Fact**
The supraspinatus muscle is often the first muscle to be affected in rotator cuff injuries, which can lead to weakness and pain in the shoulder during abduction.
**Correct Answer: A. Supraspinatus muscle.**