A patient cannot actively abduct the shoulder against gravity and has a positive drop-arm test. This finding most strongly suggests tear of which muscle?

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

Answer: (B)

The ability to initiate and hold shoulder abduction, especially around the initial 15 degrees, is powered mainly by the supraspinatus. A tear of this tendon weakens that initial lift and the ability to stabilize the arm against gravity.

A positive drop-arm test means the arm cannot be held at about 90 degrees of abduction and rather slowly drops, indicating a substantial supraspinatus tear affecting its function. Since the supraspinatus is the primary muscle for initiating abduction, its failure leads to the observed inability to abduct actively against gravity.

The other muscles listed are more involved in rotation: infraspinatus and teres minor mainly external rotation, while subscapularis mainly internal rotation. Tears in those muscles would typically present with weakness in rotation rather than a primary loss of abduction with a positive drop-arm sign. Therefore, the presentation most strongly points to a supraspinatus tear.