Total Shoulder Replacement The shoulder is the most mobile joint in the human body. The joint includes four tendons whose purpose is to hold muscle to bone. Together, these four "rotator cuff" tendons stabilize the upper arm bone to the shoulder socket and allow a wide range of motion in the shoulder. Any swelling, inflammation, tearing, or bony changes around these tendons causes pain when a person tries to move the arm above the head, behind the back, or straight out front. The technique of total shoulder replacement, also called arthroplasty, removes the damaged bone and cartilage in a joint. The bone is replaced with implants made from metal alloy and polyethylene (plastic). The purpose of the procedure is to restore movement and decrease or eliminate pain.