**Core Concept**
During shoulder abduction, a coordinated movement of the scapula, humerus, and clavicle occurs to facilitate the movement. The scapula moves upward and rotates laterally, while the humerus abducts and the clavicle elevates.

**Why the Correct Answer is Right**
The correct answer is A. Medial rotation of scapula because during shoulder abduction, the scapula actually rotates laterally, not medially. This lateral rotation allows the scapula to move upward and around the rib cage, making room for the humerus to abduct. The scapula's lateral rotation is facilitated by the serratus anterior muscle and the trapezius muscle.

**Why Each Wrong Option is Incorrect**
**Option B:** Axial rotation of humerus at acromioclavicular joint is actually a component of shoulder abduction, as the humerus rotates outward (externally) to increase the range of abduction.
**Option C:** Elevation of humerus is a correct movement taking place during shoulder abduction, as the humerus moves upward and away from the body.
**Option D:** Movements at clavicular end of sternoclavicular joint do occur during shoulder abduction, including elevation and gliding movements that allow the clavicle to move upward and forward.

**Clinical Pearl / High-Yield Fact**
To remember the movements occurring during shoulder abduction, use the mnemonic SCRAP: Scapula rotates laterally, Clavicle elevates, and Humerus abducts and rotates externally.

**✓ Correct Answer: A. Medial rotation of scapula**