Medical Services Total Joint Center Total Shoulder Find a Location Find a Provider Total Joint Center Menu Department Phone Numbers Total Knee Frequently Asked Questions Pre-op Post-op Information for Caregivers Total Hip Frequently Asked Questions Pre-op Post-op Information for Caregivers Patient Success Stories Total Shoulder Frequently Asked Questions Pre-op Post-op Total Ankle Commonwealth Orthopaedic Centers Shoulder Replacement A healthy shoulder is a ball and socket joint that is made up of three bones: the humerus (upper arm bone), the scapula (shoulder blade) and the clavicle (collar bone). The shoulder functions through the ligaments and tendons. The rotator cuff is a group of muscle and tendons that allow the arm to be lifted above the head and allows activities such as throwing a ball. When a shoulder joint becomes stiff and painful from arthritis and joint disease, the decision is usually made to perform a total shoulder replacement. This involves replacing the end of the humerus (arm bone) and the glenoid (socket). A plastic component is inserted into the socket and a metal component is placed into the humerus (arm bone). These new components allow for smoother, non-painful motion in the shoulder joint. If a rotator cuff tear is present, the surgeon may recommend a reverse total shoulder replacement. Reverse Shoulder Replacement This procedure involves replacing both the head of the humerus and the socket (glenoid); however, the prosthesis is reversed to improve muscle function. In other words, the plastic component is attached to the humeral head (arm bone), and the ball is attached to the socket area.