The shoulder has a wide and versatile range of motion. When something goes wrong with your shoulder, it hampers your ability to move freely and can cause a great deal of pain and discomfort. The shoulder is a ball-and-socket joint that has three main bones: The humerus (long, upper-arm bone), the clavicle (collarbone) and the scapula (shoulder blade). These bones are cushioned by a layer of cartilage.
There are two main joints: The acromioclavicular joint is between the highest part of the scapula and the clavicle. The glenohumeral joint is made up of the top, ball-shaped part of the humerus bone and the outer edge, or the socket, of the scapula. This joint is also known as the shoulder joint.
The shoulder joint is the most mobile joint in the body. It moves the shoulder forward and backward. It also allows the arm to move in a circular motion, and to move up and away from the body. With all these movements possible, it also the leaves the shoulder as the most unstable and vulnerable joint in the body.
Shoulders get their range of motion from the rotator cuff. The rotator cuff is made up of four muscles and their tendons. Tendons are the tissues that connect muscles to bone. It may be painful or difficult to lift your arm over your head if the tendons or bones around the rotator cuff are damaged or swollen.
You can injure your shoulder by performing manual labor, playing sports or even by repetitive movement.
The typical total shoulder replacement involves replacing the arthritic joint surfaces with a highly polished metal ball attached to a stem, and a plastic socket. These components come in various sizes. They may be either cemented or “press fit” into the bone. In most cases, an all-plastic glenoid (socket) component is implanted with bone cement.
Implantation of a glenoid component is not advised if:
- The glenoid has good cartilage
- The glenoid bone is severely deficient
- The rotator cuff tendons are irreparably torn
Patients with bone-on-bone osteoarthritis and intact rotator cuff tendons are generally good candidates for conventional total shoulder replacement.