Anatomy
Shoulder is made up of three bones, upper arm bone (humerus), shoulder blade (scapula), and 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.The muscles and tendons that surround the shoulder provide stability and support.Conditions for shoulder replacement
- Osteoarthritis (Degenerative Joint Disease)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
- Rheumatoid Arthritis : 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.”
- Post-traumatic 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.
- Rotator Cuff Tear Arthropathy 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 (Osteonecrosis): 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.
- Severe Fractures : 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 to put the pieces of bone back in place.
- Failed Previous Shoulder Replacement Surgery:-Although uncommon, some shoulder replacements fail, most often because of implant loosening, wear, infection, and dislocation. When this occurs, a second joint replacement surgery — called a revision surgery — may be necessary.
Indications for Shoulder Joint Replacement
People who benefit from surgery often have :- Severe shoulder pain that interferes with everyday activities, such as, dressing, toileting, and washing.
- Moderate to severe pain while resting. This pain may be severe enough to prevent a good night’s sleep.
- Loss of motion and/or weakness in the shoulder.
- Failure to substantially improve with other treatments such as anti-inflammatory medications, cortisone injections, or physical therapy.
- X-rays or MRI shows arthritis or other problems.
Total shoulder replacement implant
The humeral implant consists of a metal ball that replaces the head of the humerus, and a stem that is secured into the main arm bone (humerus).The humeral stem is made of titanium for maximum strength. The head is made of cobalt chrome to provide a smooth surface for movement with the glenoid component, which is made of polyethylene. The metal ball and stem are selected by the surgeon from multiple sizes to fit the contour and shape of each patient’s humerus. This two-piece construction is known as a modular implant. This modularity allows surgeons to closely replicate the natural shoulder. If the surgeon uses only the metal humeral components (humeral head and stem), the procedure is called a partial shoulder replacement. If the surgeon uses both the humeral components and the glenoid implant, the procedure is called a total shoulder replacement. Surgeons will decide which procedure to use based on the extent of damage to their patients’ shoulders.Shoulder Replacement Options
Shoulder replacement surgery is highly technical. It should be performed by a surgical team with experience in this procedure.Total Shoulder Replacement
The typical total shoulder replacement involves replacing the arthritic joint surfaces with a highly polished metal ball attached to a stem, and plastic socket.t They may be either cemented or “press fit” into the bone. If the bone is of good quality, 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 ift
- The glenoid has good cartilage
- The glenoid bone is severely deficient
- The rotator cuff tendons are irreparably torn
Shoulder Hemiarthroplasty
Depending on the condition of your shoulder, surgeon may replace only the ball. This procedure is called a hemiarthroplasty. Indications for a hemiarthroplasty include:- Arthritis that only involves the head of the humerus with a glenoid that has a healthy and intact cartilage surface
- Shoulders with severely weakened bone in the glenoid
- Some shoulders with severely torn rotator cuff tendons and arthritis the humeral head is severely fractured but the socket is normal.