Shoulder pain with weak abduction is most consistent with weakness of which muscles?

Shoulder pain with weak abduction is most consistent with weakness of which muscles?

• A. Subscapularis
• B. Teres minor
• C. Supraspinatus, deltoid
• D. Infraspinatus, teres minor

Answer: (C)

Abduction of the arm relies on two components: initiation by the supraspinatus and power from the deltoid. The supraspinatus starts the lift for the first roughly 15 degrees, while the deltoid drives abduction through the remaining range. If both are weak, the arm cannot abduct effectively, which fits shoulder pain with weak abduction. The other rotator cuff muscles have different primary actions—subscapularis for internal rotation, and infraspinatus/teres minor for external rotation—so weakness in those would show up as problems with rotation rather than the primary lifting of the arm.

Abduction of the arm relies on two components: initiation by the supraspinatus and power from the deltoid. The supraspinatus starts the lift for the first roughly 15 degrees, while the deltoid drives abduction through the remaining range. If both are weak, the arm cannot abduct effectively, which fits shoulder pain with weak abduction. The other rotator cuff muscles have different primary actions—subscapularis for internal rotation, and infraspinatus/teres minor for external rotation—so weakness in those would show up as problems with rotation rather than the primary lifting of the arm.