History and Physical Exam
There is typically pain on the superior aspect of the shoulder. They will have often fallen onto that shoulder or, less commonly, fallen onto an outstretched hand.
Examination should occur in the standing or sitting position. Many high grade AC separations can be a "doorway diagnosis" identified by simply looking at the patient. The shoulder will sag and prominent clavicle will be noted. There is tenderness to palpation over the AC joint. Shoulder range of motion is often painful. Patients will also have pain with cross arm adduction testing.