Which muscle lies at the top of the scapula above the spine and initiates abduction of the arm, while helping hold the humerus in its socket?

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

Answer: (B)

Supraspinatus sits at the top of the scapula, in the supraspinous fossa just above the spine. Its tendon threads under the acromion and attaches to the humerus, and it is responsible for initiating arm abduction—the first upward lift that gets the motion started before the deltoid takes over. At the same time, its contraction helps center and compress the humeral head into the glenoid, stabilizing the shoulder joint as the arm begins to move.

That placement and function match the description: a muscle above the spine that starts abduction and helps hold the humerus in its socket. The other rotator cuff muscles go to different regions and contribute to different actions (infraspinatus mainly external rotation and lies below the spine; subscapularis on the front and aids internal rotation; teres minor also assists with external rotation).