Review Question - QID 218079

A 54-year-old male presents to your clinic with several months of shoulder pain. He has a history of right shoulder hemiarthroplasty that was done 4 years ago after a 4-part proximal humerus nonunion and had been functioning well until recently. He denies any specific recent trauma. On examination, he is well-appearing and has no erythema about the shoulder. He has 50° of active forward flexion, 30° of abduction, and 30° of external rotation with the arm adducted. Passive range of motion is near normal without crepitus. He does have pain over the lateral deltoid region but his primary complaint is weakness and dysfunction. A radiograph is seen in Figure A. You recommend revision to reverse total shoulder arthroplasty. What is the most likely reason for the failure of his hemiarthroplasty?