During a musculoskeletal exam, the nurse asks a patient to raise their arm out to the side, away from the body. This movement is an example of:

Abduction is the coronal plane movement of a limb away from the midsagittal plane of the body. This motion is facilitated by the deltoid and supraspinatus muscles at the glenohumeral joint. It is a fundamental component of the musculoskeletal examination used to assess rotator cuff integrity and joint mobility. A. Extension: Extension involves increasing the angle between two body parts, such as moving the arm posteriorly beyond the anatomical position. It occurs in the sagittal plane rather than the coronal plane. Raising the arm out to the side does not fit the anatomical definition of extension. B. Flexion: Flexion is a movement that decreases the joint angle, typically bringing the limb forward in the sagittal plane. Examples include lifting the arm straight ahead or bending the elbow. The movement described in the question occurs in a lateral, outward direction, which is distinct from flexion. C. Abduction: The term abduction literally means "to lead away." In anatomy, this specifically refers to the lateral movement of a limb away from the body's midline. The action of raising the arm out to the side is the classic clinical example of shoulder abduction. D. Internal rotation: This movement involves rotating the humerus medially toward the center of the body around its longitudinal axis. It does not involve lifting the arm away from the trunk. Internal rotation is typically tested by having the patient place their hand behind their lower back.