Your shoulder is made up of three bones: your upper arm bone (humerus), your shoulder blade (scapula), and your collarbone (clavicle). The shoulder is a ball-and-socket joint: The ball, or head, of your upper arm bone fits into a shallow socket in your shoulder blade. This socket is called the glenoid.
The surfaces of the bones where they touch are covered with articular cartilage, a smooth substance that protects the bones and enables them to move easily. A thin, smooth tissue called synovial membrane covers all remaining surfaces inside the shoulder joint. In a healthy shoulder, this membrane makes a small amount of fluid that lubricates the cartilage and eliminates almost any friction in your shoulder.
The muscles and tendons that surround the shoulder provide stability and support.
All of these structures allow the shoulder to rotate through a greater range of motion than any other joint in the body.
In shoulder replacement surgery, the damaged parts of the shoulder are removed and replaced with artificial components, called a prosthesis.
The treatment options are either replacement of just the head of the humerus bone (ball), or replacement of both the ball and the socket (glenoid).
Several conditions can cause shoulder pain and disability, and lead patients to consider shoulder joint replacement surgery.
This is an age-related "wear and tear" type of arthritis. It usually occurs in people 50 years of age and older, but may occur in younger people, too. The cartilage that cushions the bones of the shoulder softens and wears away. The bones then rub against one another. Over time, the shoulder joint slowly becomes stiff and painful.
Unfortunately, there is no way to prevent the development of osteoarthritis. It is a common reason people have shoulder replacement surgery.
This is a disease in which the synovial membrane that surrounds the joint becomes inflamed and thickened. This chronic inflammation can damage the cartilage and eventually cause cartilage loss, pain, and stiffness. Rheumatoid arthritis is the most common form of a group of disorders termed "inflammatory arthritis."
This can follow a serious shoulder injury. Fractures of the bones that make up the shoulder or tears of the shoulder tendons or ligaments may damage the articular cartilage over time. This causes shoulder pain and limits shoulder function.
A patient with a very large, long-standing rotator cuff tear may develop cuff tear arthropathy. In this condition, the changes in the shoulder joint due to the rotator cuff tear may lead to arthritis and destruction of the joint cartilage.
Avascular necrosis is a painful condition that occurs when the blood supply to the bone is disrupted. Because bone cells die without a blood supply, osteonecrosis can ultimately cause destruction of the shoulder joint and lead to arthritis. Chronic steroid use, deep sea diving, severe fracture of the shoulder, sickle cell disease, and heavy alcohol use are risk factors for avascular necrosis.
A severe fracture of the shoulder is another common reason people have shoulder replacements. When the head of the upper arm bone is shattered, it may be very difficult for a doctor to put the pieces of bone back in place. In addition, the blood supply to the bone pieces can be interrupted. In this case, a surgeon may recommend a shoulder replacement. Older patients with osteoporosis are most at risk for severe shoulder fractures.
Shoulder replacement surgery is highly technical. It should be performed by a surgical team with experience in this procedure.
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. If the bone is of good quality, your surgeon may choose to use a non-cemented (press-fit) humeral component. If the bone is soft, the humeral component may be implanted with bone cement. In most cases, an all-plastic glenoid (socket) component is implanted with bone cement.
Implantation of a glenoid component is not advised if:
Patients with bone-on-bone osteoarthritis and intact rotator cuff tendons are generally good candidates for conventional total shoulder replacement.
Depending on the condition of your shoulder, your surgeon may replace only the ball. This procedure is called a hemiarthroplasty. In a traditional hemiarthroplasty, the head of the humerus is replaced with a metal ball and stem, similar to the component used in a total shoulder replacement. This is called a stemmed hemiarthroplasty.
Some surgeons recommend hemiarthroplasty when the humeral head is severely fractured but the socket is normal. Other indications for a hemiarthroplasty include:
Sometimes, surgeons make the decision between a total shoulder replacement and a hemiarthroplasty in the operating room at the time of the surgery.
Studies show that patients with osteoarthritis get better pain relief from total shoulder arthroplasty than from hemiarthroplasty.
Resurfacing hemiarthroplasty involves replacing just the joint surface of the humeral head with a cap-like prosthesis without a stem. With its bone preserving advantage, it offers those with arthritis of the shoulder an alternative to the standard stemmed shoulder replacement.
Resurfacing hemiarthroplasty may be an option for you if:
For patients who are young or very active, resurfacing hemiarthroplasty avoids the risks of component wear and loosening that may occur with conventional total shoulder replacements in this patient population. Due to its more conservative nature, resurfacing hemiarthroplasty may be easier to convert to total shoulder replacement, if necessary at a later time.
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