Review Question - QID 210887

A 33-year-old man presents to his primary care physician with shoulder pain. He states that he can't remember a specific instance when the injury occurred. He is a weightlifter and competes in martial arts. The patient has no past medical history and is currently taking a multivitamin. His temperature is 99.3°F (37.4°C), blood pressure is 123/65 mmHg, pulse is 70/min, respirations are 12/min, and oxygen saturation is 98% on room air. Physical exam demonstrates pain with abduction of the patient's right shoulder and with external rotation of the right arm. There is subacromial tenderness with palpation. His left arm demonstrates 10/10 strength with abduction as compared to 4/10 strength with abduction of the right arm. Which of the following is the most accurate method of confirming the underlying diagnosis?