REVERSE In a Reverse Total shoulder the ball is located on the shoulder blade (glenoid) and the socket is located on the arm bone (humerus), exactly the opposite of the situation in a conventional total shoulder. The ball (glenosphere) is screwed to the bone of the shoulder blade. The cup (humeral sock¬et) is fixed to a stem that is cemented down the inside of the arm bone (humerus). This configuration provides sta¬bility because the muscles around the shoulder compress the ball and socket together.