Which rotator cuff muscle is not primarily involved in initiation of abduction?

Which rotator cuff muscle is not primarily involved in initiation of abduction?

• A. Supraspinatus
• B. Infraspinatus
• C. Teres minor
• D. Subscapularis

Answer: (D)

When starting to lift the arm, the first move comes from the supraspinatus. It generates the initial abduction moment and helps center the humeral head in the glenoid as the deltoid takes over the higher range of motion. The subscapularis, by contrast, is mainly an internal rotator and a stabilizer that keeps the humeral head centered from the front. It doesn’t contribute to beginning the abduction, so it isn’t primarily involved in initiating that movement. The infraspinatus and teres minor are external rotators and also help stabilize the joint; they support the movement but are not the primary initiators of abduction.

When starting to lift the arm, the first move comes from the supraspinatus. It generates the initial abduction moment and helps center the humeral head in the glenoid as the deltoid takes over the higher range of motion. The subscapularis, by contrast, is mainly an internal rotator and a stabilizer that keeps the humeral head centered from the front. It doesn’t contribute to beginning the abduction, so it isn’t primarily involved in initiating that movement. The infraspinatus and teres minor are external rotators and also help stabilize the joint; they support the movement but are not the primary initiators of abduction.