Shoulder Prosthesis: Applications & Health Benefits

An artificial shoulder joint is called a shoulder prosthesis. It is used to replace worn or injured joint surfaces of the shoulder.

What is a shoulder replacement?

A shoulder prosthesis is used primarily in cases of osteoarthritis of the shoulder joint. A shoulder prosthesis is a joint replacement for the shoulder. It is used as part of a surgical implantation to replace shoulder joint surfaces that have been destroyed by wear or injury. A shoulder prosthesis is primarily used in cases of arthrosis of the shoulder joint. Osteoarthritis is said to occur when there is abrasion of the joint cartilage. Without intact articular cartilage, the shoulder joint cannot be used without pain. Other possible indications for a shoulder prosthesis are bone fractures that result in the destruction of the shoulder, which in turn negatively affects its functionality. In rare cases, the insertion of a shoulder prosthesis also takes place because the humeral head has died or the patient suffers from a tumor in the upper arm. In Germany, about 3,000 shoulder prostheses are used each year, which is a rather low number compared to hip and knee prostheses. The long-term durability of the prostheses is similar to that of artificial hip and knee joints.

Forms, types, and styles

Physicians distinguish between different types of shoulder prostheses. These include the humeral head prosthesis (hemiprosthesis), the surface replacement prosthesis, the total endoprosthesis (TEP), and the inverse shoulder prosthesis. The hemiprosthesis is used to replace only the humeral head. It is anchored in the bone shaft. Primarily, cement made of hard plastic is used for fixation. Alternatively, however, a cement-free version can also be used. A special coating gives the bone the opportunity to grow. The stability of the hemiprosthesis is on average 10 years. Only about one percent of artificial shoulder joints require replacement. A metal cap is used for a surface replacement prosthesis. It is attached to the upper arm joint surface. To provide sufficient support for the surface replacement, it is necessary to remove the old cartilage surface. However, the surface replacement prosthesis is only suitable for minor damage to the shoulder. Thus, in the case of larger defects, not enough support can be found for the anchoring. A total shoulder arthroplasty is used if there is also cartilage damage to the glenoid. A humeral head prosthesis is then no longer considered adequate. It is important to implant a glenoid replacement, which is made of plastic. It is anchored in the bone with a peg. A total endoprosthesis is not suitable if there is damage to the bone or if it is too soft. In general, the total endoprosthesis is considered more susceptible than the hemiprosthesis. Thus, within 10 years, loosening requiring treatment occurs in 5 to 10 percent of these prostheses. If the rotator cuff muscles have also been affected, an inverse shoulder prosthesis is used. In this case, the surgeon screws the artificial joint head onto the former socket. The new socket is then attached inside the humeral head with cement.

Structure and function

The structure of a shoulder prosthesis corresponds to the structure of the human shoulder joint. Depending on the variant of the prosthesis, the artificial shoulder joint consists of three components. These are the prosthesis stem, the humeral head component, and the artificial glenoid cavity. The humeral head component consists of a metal cap, which is attached to the humeral head, or a metal head. This is seated on a prosthesis stem, which is implanted in the humerus in advance. Conventional shaft prostheses, short shaft prostheses or long shaft prostheses can basically be used for the prosthesis shaft. A total shoulder prosthesis also receives an artificial glenoid replacement, which acts as a counterpart for the humeral head prosthesis metal head. In order for the shoulder prosthesis to perform its function in the shoulder joint permanently, it must be made of material that does not wear out prematurely or cause rejection. Thus, materials are used that are long-lasting and considered compatible with the body. These are mostly polymers (plastics), ceramics and special metals.While chromium-cobalt alloys or titanium are used for a humeral head prosthesis, a total shoulder prosthesis is usually composed of polyethylene, a hard plastic. Sometimes, however, metal or ceramic can also be used. In this case, the articular cartilage of the shoulder joint is imitated and acts as a sliding surface. Ultimately, however, the individual characteristics of the patient determine which material the surgeon uses. Despite their increasingly high quality, shoulder prostheses cannot match the quality of the original joint. To ensure that the artificial shoulder joint lasts as long as possible, the patient should exercise as few jerky movements as possible and refrain from certain sports such as tennis or boxing.

Medical and health benefits

The health benefit of a shoulder replacement is the replacement of the worn shoulder joint. It is used when the affected person’s pain can no longer be controlled by conservative means such as pain pills or injections. Ultimately, the decisive factor is how severely the patient suffers from shoulder pain and restricted movement. By implanting a shoulder prosthesis, it is usually possible to achieve a significant reduction in pain and increase the mobility of the shoulder. Targeted follow-up treatment is also important for this. The timing of the implantation plays an important role in the positive benefit of the prosthesis. If there is already an inflamed humeral head, reductions in the muscles or weakness in external rotational movements of the arm, at least the pain can be reduced. However, if there are adhesions to the joint capsule and the muscles and tendons, this reduces the mobility of the shoulder. A shoulder prosthesis should therefore be used as long as the arm can still be rotated in the outer direction. In principle, a shoulder prosthesis ensures that the mobility of the shoulder is subsequently increased again, which improves the patient’s quality of life.