Which rotator cuff muscle initiates abduction of the arm?

Which rotator cuff muscle initiates abduction of the arm?

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

Answer: (A)

Initiating abduction from the side is started by the supraspinatus. This rotator cuff muscle sits in the supraspinous fossa and its tendon runs under the acromion to the greater tubercle of the humerus. When it contracts, it lifts the humeral head into the glenoid and begins the arm’s upward movement, roughly the first 15 degrees. After that initial lift, the deltoid takes over to continue raising the arm. The other rotator cuff muscles mainly rotate the shoulder or stabilize the joint (infraspinatus and teres minor are external rotators; subscapularis is an internal rotator), so they don’t initiate abduction.

Initiating abduction from the side is started by the supraspinatus. This rotator cuff muscle sits in the supraspinous fossa and its tendon runs under the acromion to the greater tubercle of the humerus. When it contracts, it lifts the humeral head into the glenoid and begins the arm’s upward movement, roughly the first 15 degrees. After that initial lift, the deltoid takes over to continue raising the arm. The other rotator cuff muscles mainly rotate the shoulder or stabilize the joint (infraspinatus and teres minor are external rotators; subscapularis is an internal rotator), so they don’t initiate abduction.