A 52-year-old right-handed carpenter presents with 3 months of progressive right shoulder pain and weakness. He reports difficulty initiating arm abduction and lifting objects overhead. On examination, the **Empty Can (Jobe) test** is positive, with pain and weakness when the arm is held abducted 90°, forward-flexed 30° in the scapular plane with thumbs pointing downward, and downward pressure is applied. MRI confirms a full-thickness tear of the structure marked **A** in the diagram. Which of the following best explains why the structure marked **A** is the most commonly torn rotator cuff tendon?

Explanation

## Why option 1 is correct The supraspinatus tendon passes through the narrow subacromial space, where it is mechanically impinged between the acromion superiorly and the humeral head inferiorly. This anatomical vulnerability, combined with repetitive overhead activities and age-related degenerative changes, makes it the most commonly torn rotator cuff tendon. The positive Empty Can test (Jobe test) in this patient—performed with the arm abducted 90° and forward-flexed 30° in the scapular plane—specifically isolates supraspinatus function and confirms its pathology. Gray's Anatomy and Apley's Orthopedics emphasize this subacromial impingement as the primary reason for supraspinatus vulnerability. ## Why each distractor is wrong - **Option 2**: The supraspinatus is innervated by the suprascapular nerve (C5-C6), not the axillary nerve. The axillary nerve innervates the deltoid and teres minor. Axillary nerve injury causes deltoid paralysis and loss of shoulder abduction beyond 15°, not supraspinatus tears. - **Option 3**: The supraspinatus is located in the supraspinous fossa on the posterior shoulder, not the anterior shoulder. The subscapularis (structure D) is the anterior rotator cuff muscle. Supraspinatus tears result from subacromial impingement, not direct anterior trauma. - **Option 4**: The supraspinatus attaches to the greater tubercle (not lesser tubercle) of the humerus. The lesser tubercle is the attachment site of the subscapularis. The mechanical disadvantage in supraspinatus pathology stems from subacromial compression, not from its humeral attachment. **High-Yield:** Supraspinatus = most common rotator cuff tear due to subacromial impingement; Empty Can test = gold standard clinical test for supraspinatus pathology; MRI = gold standard imaging for soft tissue confirmation. [cite: Gray's Anatomy 42e Ch 49; Apley 10e]