Joint replacement

Great advances have been made in joint replacement in the United States sincethe first hip was replaced in 1969. Improvements have been made in the materials and the surgical techniques used to install artificial joints.

Custom joints can be made using a mold that duplicates the original with a very high degree of accuracy.

The most common joints to be replaced are hips and knees. There is ongoing work on elbow and shoulder replacement, but some joint problems are still treated by surgically removing the joint in question or by reassembling the jointfrom smaller parts.

Seventy percent of replacements are performed because arthritis has caused the joint to stiffen and become painful to the point where normal daily activities are no longer possible. Joint replacement is appropriate if the joint doesn't respond to conservative treatment such as medication, weight loss, restricting activity and canes.

Patients with rheumatoid arthritis or other connective tissue diseases may also be candidates for joint replacement, but the results are usually not as good. Elderly people who fall and break a hip often undergo hip replacement when the probability of successful bone healing is low.

More than 170,000 hip replacements are performed in the United States each year. Since the lifetime of the artificial joint is limited, the best candidates for joint replacement are over age 60. In fact, joint replacements are performed successfully on an older-than-average group of patients. People with diseases that interfere with blood clotting are not good candidates, nor wouldanyone with any heart, kidney or lung problems that would make it risky to undergo general anesthesia.

Joint replacements are performed under general or regional anesthesia in a hospital by an orthopedic surgeon. Some medical centers specialize in joint replacement, and these centers generally have a higher success rate than less specialized facilities. The specific techniques of joint replacement vary depending on the joint involved.

In a hip replacement, the surgeon makes an incision along the top of the thigh bone and pulls it away from the socket of the hip bone. Next, the doctor inserts an artificial socket made of metal coated with plastic to reduce friction. After cutting the top of the thigh bone, the doctor fits a piece of artificial thigh made of metal into the lower thigh bone on one end and the new socket on the other. The artificial hip can either be held in place by a synthetic cement or by natural bone in-growth.

While the cement is good at locking the prosthesis to the remaining bone, bubbles left in the cement after it cures may act as weak spots, causing cracksto develop. This promotes loosening of the prosthesis later in life. If moresurgery is needed, all the cement must be removed before surgery can be performed.

On the other hand, an artificial hip fixed by natural bone in-growth requiresmore precise surgical techniques to assure maximum contact between the remaining natural bone and the prosthesis. The prosthesis is made so that it contains small pores that encourage the natural bone to grow into it. Growth begins 6 to 12 weeks after surgery. The short-term outcome with non-cemented hipsis less satisfactory (patients report more thigh pain) but the long-term outlook is better with this technique. In both methods, hospital stays last from four to eight days.

In a knee replacement, the doctor makes a cut to expose the knee joint and then loosens the ligaments surrounding the knee. Next, the surgeon cuts the shin and thigh bone, and removes the knee. The artificial knee is cemented intoplace on the remaining stubs of those bones, the excess cement is removed andthe knee is closed. Hospital stays range from three to six days.

In both types of surgery, preventing infection is very important. Antibioticsare given intravenously and continued in pill form after the surgery. Fluidand blood loss can be great, and sometimes blood transfusions are needed. Many patients choose to donate their own blood for transfusion during the surgery. This prevents any blood incompatibility problems or the transmission of bloodbourne diseases.

Immediately after the operation the patient will be catheterized and monitored for infection. Antibiotics are continued and pain medication is prescribed.Physical therapy begins (first passive exercises, then active ones) as soon as possible using a walker, cane, or crutches for additional support.

The immediate risks during and after surgery include infection, the development of blood clots that may block the arteries, and loss of too much blood. Infection caused by the operation can occur as long as a year later and can bedifficult to treat. Some doctors add antibiotics directly to the cement usedto fix the replacement joint in place. Blood-thinning medication is usually given to reduce the risk of clots. Loosening of the joint is the most common cause of failure in hip joints that are not infected. This may require anotherjoint replacement surgery in about 12% of patients within a 15-year period following the first procedure.

Some elderly people experience short-term confusion and disorientation from the anesthesia. Although joint replacement surgery is highly successful, thereis a risk of nerve injury. Dislocation or fracture of the hip joint is alsoa possibility.

More than 90% of patients receiving hip replacements have no more relief andmuch better joint function. The success rate is slightly lower in knee replacements, and drops still more for other joint replacement operations.

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