SHOULDER JOINT REPLACEMENT

Many people know someone with an artificial knee or hip joint. Less common, but just as successful in relieving joint pain, is a shoulder replacement (arthroplasty). This procedure may be recommended if arthritis or degenerative joint disease makes your shoulder stiff and painful or if the upper arm bone is fractured so badly that tissue death may result.

The shoulder is a ball-and-socket joint that enables you to raise, twist, bend, and move your arms forward, to the sides and behind you. The head of the upper arm bone (humerus) is the ball and a circular depression (glenoid) in the shoulder bone (scapula) is the socket. A soft-tissue rim (labrum) surrounds and deepens the socket. The head of the upper arm bone is coated with a smooth, durable covering (articular cartilage) and the joint has a thin, inner lining (synovium) for smooth movement. The surrounding muscles and tendons provide stability and support.

IMPLANT DESIGN AND CONSTRUCTION

Shoulder replacement surgery replaces damaged surfaces with artificial parts (prostheses). Usually, there are two components:

• The humeral component replaces the head of the upper arm bone. It is made of metal (usually cobalt/chromium-based alloys) and has a rounded ball attached to a stem that fits into the bone. This component comes in various sizes and can be a single piece or a modular unit.
• The glenoid component replaces the socket (the glenoid depression). It is made of ultrahigh density polyethelene. Some versions have a metal tray, but totally plastic versions are more common.

Depending on the damage to your shoulder, the surgeon may replace just the humeral head (a hemiarthroplasty) or both the humeral head and the glenoid (total shoulder replacement). The components come in various sizes and shapes and are held in place with either acrylic bone cement (cemented) or bone ingrowth (cementless). As in the natural joint, the surrounding muscles and tendons provide stability for the prosthesis.

Shoulder replacement surgery is highly technical and should be performed by a surgical team with experience in this procedure. Each case is individual and your surgeon will evaluate your situation carefully before making any decisions. Do not hesitate to ask what type of implant will be used in your situation and why that choice is appropriate for you.

IMPLANT INSERTION

Either regional or general anesthesia may be used during shoulder replacement surgery. Your physician or anesthesiologist will discuss the best type of anesthesia to use in your situation. The surgical incision is 3" to 4" long and is made on the front of the shoulder from the collarbone (clavicle) to the point where the shoulder muscle (deltoid) attaches to the upper arm bone. The surgeon will be very careful not to injure any of the nerves or blood vessels that cross the shoulder and will inspect the muscles to see if any are torn or damaged.

The upper arm bone is dislocated from the socket to expose the ball-like end of the upper arm. Only the portion of the bone covered by articular cartilage is removed. The center cavity of the bone is cleaned and enlarged with reamers of gradually increasing size to create a hollow that matches the shape of the implant stem. The top end of the bone is smoothed so the stem can be inserted flush with the bone surface. If the ball is a separate piece, the proper size is selected and attached.

If the socket portion of the joint is basically healthy and the surrounding muscles are intact, the surgeon may decide not to replace it. However, if the socket is damaged, the upper arm bone is moved to the back and the surgeon will implant the glenoid component. The surgeon prepares the socket surface by removing the remaining damaged cartilage. The socket bone is then gently reamed to match the implant. Protrusions on the polyethylene component are then fitted into holes drilled in the socket surface. Once a precise fit is achieved, the component is cemented into position. The arm bone, with its new prosthetic head, is replaced in the socket. The surgeon reattaches the supporting tendons and closes the incision. The 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 fluids and is usually removed on the day after surgery.

POSTOPERATIVE REHABILITATION

A careful, well-planned rehabilitation program is critical to the success of a shoulder replacement. If the surgery is scheduled for the morning, therapy can begin that afternoon, and no later than the first postoperative day. A physical therapist will initiate gentle, passive-assisted range of motion exercises. Before you leave the hospital (usually two or three days after surgery), your therapist will instruct you in how to use a pulley device to help bend and extend your arm.

Here are some do's and don'ts for when you return home:

• Do wear the sling every night for at least the first month.
• Don't use your arm to push yourself up in bed or from a chair because this requires forceful contraction of muscles.
• Do follow the program of home exercises prescribed for you. You may need to do the exercises 4 to 5 times a day for a month or more.
• Don't overdo it! If your shoulder pain was severe before the surgery, the experience of pain-free motion may lull you into thinking that you can do more than is prescribed. Early overuse of the shoulder may result in severe limitations in motion.
• Don't lift anything heavier than a cup of coffee for the first 6 weeks after surgery.
• Do ask for assistance. Your physician may be able to recommend an agency or facility if you do not have home support.
• Don't participate in contact sports or do any heavy lifting for at least 6 months.

COMPLICATIONS

Complications after shoulder replacement surgery occur less frequently than with other joint replacement surgeries. However, there are risks. Infection, intraoperative fracture of the upper arm bone or postoperative fractures, postoperative instability and loosening of the glenoid component are the most common complications. Advances in surgical techniques and prosthetic innovations are helping to reduce the occurrence of complications.

Our compliments to the American Academy of Orthopedic Surgeons for the above information relating to Should Joint Replacement. For more information, please visit the AAOS by clicking on the AAOS website.