A 55 year-old patient presents with shoulder pain after falling during an ice storm. On examination, there is localized shoulder pain when the advanced practice registered nurse (APRN) performs the "crossover test" (arm moved across the chest toward the opposite side while extended at the elbow). Which of the following is the most likely site of injury?

Shoulder injuries following trauma are evaluated using specific physical examination maneuvers that help localize the affected anatomical structure. The crossover test (also known as the horizontal adduction or scarf test) is used to assess pathology of the acromioclavicular (AC) joint. Pain elicited when the arm is moved across the chest indicates stress or inflammation of this joint. Accurate interpretation of special tests helps differentiate AC joint injury from rotator cuff, biceps tendon, or glenohumeral pathology. Rationale: A. Rotator cuff injuries typically present with pain during abduction, especially between 60–120 degrees (painful arc), and weakness with shoulder movement. These injuries are associated with positive drop arm or empty can tests rather than pain specifically with horizontal adduction across the chest. The crossover test is not specific for rotator cuff pathology. B. Bicipital tendon pathology presents with anterior shoulder pain and tenderness over the bicipital groove. Pain is typically reproduced with Speed’s or Yergason’s tests rather than the crossover maneuver. The localization of pain in this case does not match the anterior tendon involvement typical of biceps tendinitis. C. Glenohumeral joint injury involves deep shoulder pain, reduced range of motion, and instability, often worsened by active and passive movement in multiple planes. It is not specifically reproduced by horizontal adduction across the chest. The crossover test is more targeted to the AC joint rather than the glenohumeral articulation. D. Acromioclavicular joint is the most likely site of injury because the crossover test places stress directly on this joint by horizontally adducting the arm across the body. Pain reproduced with this maneuver indicates AC joint irritation or separation, commonly seen after falls onto the shoulder. This test is highly specific for AC joint pathology, making it the correct answer.