<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A 65-year-old man comes to the physician for evaluation of severe pain in his left shoulder for several days. He did not fall or injure his shoulder. He has a history of osteoarthritis of both knees that is well-controlled with indomethacin. He spends most of his time at a retirement facility and does not do any sports. There is no family history of serious illness. He has smoked one pack of cigarettes daily for 35 years. Vital signs are within normal limits. Physical examination shows tenderness of the greater tuberosity of the left humerus. There is no swelling or erythema. The patient is unable to slowly adduct his arm after it is passively abducted to 90 degrees. External rotation is limited by pain. Subacromial injection of lidocaine does not relieve his symptoms. An x-ray of the left shoulder shows sclerosis of the acromion and humeral head. Which of the following is the most appropriate next step in management?? A: Musculoskeletal ultrasound, B: CT scan of the shoulder, C: Surgical fixation, D: Biopsy of the humerus, E: Reassurance,  <response>: This is a patient with acute shoulder pain and limited range of motion, most concerning for rotator cuff tear. Key findings include tenderness over the greater tuberosity, painful limited abduction and external rotation, and lack of improvement with subacromial lidocaine injection. X-ray shows degenerative changes. The history and physical exam are most consistent with rotator cuff tear. Musculoskeletal ultrasound is the appropriate next step to evaluate the rotator cuff and confirm the diagnosis. CT scan would provide bony detail but not visualize soft tissues like the rotator cuff. Surgical fixation would be premature without confirming the diagnosis. Biopsy of the humerus is unnecessary. Reassurance alone would be inappropriate for acute severe shoulder pain requiring further evaluation.A: Musculoskeletal ultrasound 