The Empty Can and Full Can tests primarily assess which muscle?

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

Answer: (A)

The main idea these tests probe is the health of the supraspinatus tendon within the rotator cuff. The supraspinatus is the muscle that initiates arm abduction and helps stabilize the humeral head under the acromion, making it the primary structure stressed during these maneuvers.

In the empty can position, the arm is raised to about 90 degrees in the scapular plane with the thumb pointed downward (internal rotation). The examiner provides downward resistance. If this elicits pain or weakness, it suggests supraspinatus tendinopathy or a tear, because this orientation places the tendon directly under the subacromial space where impingement or degeneration commonly occurs.

In the full can position, the same elevation is used but with external rotation (thumb up), which reduces impingement and better isolates the supraspinatus. A positive result here reinforces supraspinatus involvement, since the test is designed to stress that tendon while minimizing contributions from other rotator cuff muscles.

These tests are not primarily used to assess the infraspinatus, subscapularis, or teres minor, which are better evaluated with tests that specifically load those muscles (for example, resisted external rotation for infraspinatus and teres minor, or bear hug/lixed tests for subscapularis).