Shoulder Replacement 🦾 Conventional Shoulder Replacement mimics the normal anatomy of the shoulder: a plastic cup is fitted into the #shoulder socket (glenoid), and a metal ball is attached to the top of the upper arm bone (humerus). In a #reverseshoulderreplacement the socket and metal ball are switched. The metal ball is fixed to the socket, and the plastic cup is fixed to the upper end of the humerus. . Reverse total shoulder replacement works better for people with cuff tear arthropathy bec