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What is shoulder joint replacement?
Shoulder joint replacement surgery is performed to replace a shoulder joint with artificial components (prostheses) when the joint is severely damaged by such degenerative joint diseases as arthritis, or in complex cases of upper arm bone fracture.

The shoulder is a ball-and-socket joint that allows the arms to be raised, twisted, bent, and moved forward, to the side and backward. The head of the upper arm bone (humerus) is the ball, and a circular cavity (glenoid) in the shoulder blade (scapula) is the socket. A soft-tissue rim (labrum) surrounds and deepens the socket. The head of the humerus is also covered with a smooth, tough tissue (articular cartilage); and the joint, also called the acromioclavicular (AC) joint, has a thin inner lining (synovium) that facilitates movement while surrounding muscles and tendons provide stability and support.

Why is shoulder joint replacement performed?
Damage to the AC joint is usually assessed using X rays of the joint and humerus. They provide information on the state of the joint space, the position of the humeral head in relation to the glenoid, the presence of bony defects or deformity, and the quality of the bone. If glenoid wear is observed, a computed tomography (CT) scan is usually performed to evaluate the degree of bone loss.
The following conditions can damage the AC joint to such an extent requiring replacement by artificial components:
  • Osteoarthritis: This is a degenerative joint disease characterized by destruction or thinning of the articular cartilage. When non-surgical treatment is no longer effective and shoulder resection not possible, joint replacement surgery is usually indicated.
  • Rheumatoid arthritis: Shoulder replacement surgery is the most commonly performed procedure for the arthritic shoulder with severe inflammatory or rheumatoid arthritis.
  • Severe fracture of the humerus: A fracture of the upper arm bone can be so severe as to require replacement of the AC joint.
  • Osteonecrosis: This condition usually follows a three- or four-part fracture of the humeral head that disrupts the blood supply, resulting in bone death and disruption of the AC joint.
  • Charcot's arthropathy: Also called neuropathic arthropathy or arthritis, Charcot's arthropathy is a condition in which the shoulder joint is destroyed following loss of its nerve supply.

Shoulder joint replacement surgery can either replace the entire AC joint, in which case it is referred to as total shoulder joint replacement or total shoulder arthroplasty; or replace only the head of the humerus, in which case the procedure is called a hemiarthroplasty.

The two artificial components that can be implanted in the shoulder during shoulder joint replacement surgery are:
  • The humeral component. This part replaces the head of the humerus. It is usually made of cobalt or chromium-based alloys and has a rounded ball attached to a stem that can be inserted into the bone. It comes in various sizes and may consist of a single piece or a modular unit.
  • The glenoid component. This component replaces the glenoid cavity. It is made of very high-density polyethylene. Some models feature a metal tray, but the 100% polyethylene type is more common.
What should I expect during my surgery?
Shoulder joint replacement surgery is performed under general anesthesia. The surgeon makes a 34 inch incision on the front of the shoulder. The surgeon inspects the muscles to see if any are damaged. He or she then proceeds to dislocate the humerus from the socket-like glenoid cavity to expose the head of the humerus. Only the portion of the head covered with articular cartilage is removed. The center cavity of the humerus (humeral shaft) is then cleaned and enlarged with reamers of gradually increasing size to create a cavity matching the shape of the implant stem. The top end of the bone is smoothed so that the stem can be inserted flush with the bone surface.

If the glenoid cavity of the AC joint is not damaged and the surrounding muscles are intact, the surgeon does not replace it, thus performing a simple hemiarthroplasty. However, if the glenoid cavity is damaged or diseased, the surgeon moves the humerus to the back and implants the artificial glenoid component as well. The surgeon prepares the surface by removing the cartilage and equalizes the glenoid bone to match the implant. Protrusions on the polyethylene glenoid implant are then fitted into holes drilled in the bone surface. Once a precise fit is achieved, the implant is cemented into position. The humerus, with its new implanted artificial head, is replaced in the glenoid socket. The surgeon reattaches the supporting tendons and closes the incision.

What should I expect after my surgery?
Following surgery, the operated arm is placed in a sling, and a support pillow is placed under the elbow to protect the repair. A drainage tube is used to remove excess fluid and is usually removed on the day after surgery.

A careful and well-planned rehabilitation program is very important for the successful outcome of a shoulder joint replacement. It should start no later than the first postoperative day. A physical therapist usually starts the patient with gentle, passive-assisted range of motion exercises. Before the patient leaves the hospital (usually two or three days after surgery), the therapist provides instruction on the use of a pulley device to help bend and extend the operated arm.

Pain relief is expected after shoulder joint replacement because the diseased joint surfaces have been replaced with smooth gliding surfaces. Improved motion, however, is variable and depends on the following:
          • The surgeon's ability to reconstruct the shoulder's supporting tissues, namely the shoulder ligaments, capsule, and muscle attachments.
          • The patient's preoperative muscle strength.
          • The patient's motivation and compliance in participating in postoperative rehabilitation therapy


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