Shoulder joint replacements come in several types. Some are cemented in place, while others aren’t. Sometimes the complete joint is replaced, while in other cases only half of the joint must be replaced.
Most of the time, the cause of the problem is osteoarthritis of the joint. The head of the humerus (upper arm bone) develops bone spurs and the joint space gets smaller. This usually results in pain, stiffness, and loss of motion. In some cases, the rotator cuff is torn. The rotator cuff is a group of four muscles whose tendons surround the shoulder joint. The tear can be small (partial tear) or large (complete tear).
Over 500 cases of shoulder joint replacement were followed by a group of 57 doctors in nine countries. The focus of the study was to see if tears in the rotator cuff needed to be repaired at the time of the joint replacement.
It seems that small tears of a single tendon don’t affect the outcome. A much greater problem is fatty degeneration in the shoulder muscles. This is a condition in which the muscle fibers are replaced by fat tissue. The reason for this is unknown. It’s likely that age has something to do with it. Fatty degeneration is more likely to occur in muscles that have been damaged or injured.
The presence of fatty degeneration in the rotator cuff means greater pain, less motion, and less strength after shoulder replacement. Still, even with fatty degeneration, the results are better with shoulder joint replacement than without.