When a person goes in with shoulder pain, why don't they recognize the bone structure of the entire shoulder and arm, one side compared to the other?

Dr can compare sides. A doctor can compare a patient's right and left sides if one side has a problem. For the shoulders, the patient can take off his shirt and hop onto the exam table without the doctor asking. That way, the doctor sees both shoulders. The patient can also point to his good shoulder and say, "see, my good side looks different or feels differently compared to my bad side".