Three weeks after a shoulder contusion, an elderly patient cannot actively abduct despite normal passive ROM. Which diagnosis best explains this finding?

• A. Rotator cuff tear
• B. Adhesive capsulitis
• C. Supraspinatus tendonitis
• D. Biceps tendon rupture

Answer: (A)

The key idea is that loss of active abduction with normal passive ROM points to a problem with the shoulder’s musculotendinous units, not the joint capsule. The supraspinatus muscle, part of the rotator cuff, initiates the first part of abduction and helps stabilize the head of the humerus. If the rotator cuff is torn, especially after a traumatic contusion in an older adult, the ability to actively abduct is weakened or lost even though the joint itself can still move through its full range when someone else moves it or when the muscle is relaxed.

Adhesive capsulitis would restrict both active and passive ROM because the joint capsule becomes stiff, not just weaken the muscle. Biceps tendon rupture typically affects elbow flexion and forearm actions, not the shoulder’s ability to abduct. Supraspinatus tendonitis can cause pain during abduction and some weakness, but passive ROM remains normal and the limitation is usually due to pain rather than a complete inability to abduct. Therefore, the most likely diagnosis is a rotator cuff tear.