Knee joint replacement

Definition

Knee joint replacement is the surgical removal of a damaged knee joint and replacing it with an artificial knee joint (prosthesis). Sometimes only a portion of the knee joint is removed and replaced.

Purpose

The most common reason for having a knee replaced is osteoarthritis , according to the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS). This degenerative joint disease, marked by the breakdown of the joint's cartilage, most commonly affects people over age 45, although younger men and women also can get this disease. Some people are born with a deformed joint or defective cartilage, which leads to osteoarthritis. Excess weight, joint fracture, ligament tears, or other injury can damage cartilage and cause osteoarthritis. Rheumatoid arthritis is another condition that may be alleviated by knee joint replacement. This chronic inflammation of the knee joint lining causes pain , stiffness, and swelling. The inflamed lining can invade and damage bone and cartilage. Rheumatoid arthritis generally starts in middle age. The risk of osteoarthritis and rheumatoid arthritis increases with age. Loss of bone caused by poor blood supply (avascular necrosis) and bone tumors are other reasons for joint replacement.

Precautions

Knee joint replacement is usually not recommended for people with:

• A current knee infection.
• Poor skin cover around the knee.
• Paralysis of the quadriceps, the muscles in the front of the thigh.
• Severe peripheral vascular disease (hardening of the arteries) or neuropathy that affects the knee.
• Severe mental problems.
• A terminal disease, such as cancer that has metastasized (spread beyond the original cancer site).
• Morbid obesity (more than 300 pounds).

Description

Joints are formed by the ends of two or more bones connected by tissue called cartilage. Healthy cartilage serves as a protective cushion, allowing smooth, low-friction movement of the joint. If the cartilage becomes damaged by disease or injury, the tissues around the joint become inflamed, causing pain. With time, the cartilage wears away, allowing the rough edges of bone to rub against each other, causing more pain. When only some of the joint is damaged, a surgeon may be able to repair or replace just the damaged parts. When the entire joint is damaged, a total joint replacement is done. To replace a total knee joint, a surgeon removes the diseased or damaged parts and inserts artificial parts, called prostheses or implants. These prostheses are considered medical devices, which are regulated by the United States Food and Drug Administration (FDA). In 2006, there were 400,000 knee joint replacement surgeries in the United States. By 2030, the number will increase to 3.5 million a year, estimates the American Academy of Orthopaedic Surgeons (AAOS). In Canada, there were 33,590 knee replacement surgeries in 2004–2005, with the highest number (12,488) occurring in the age group of 65–74. In the past, patients between 60 and 75 years of age were considered to be the best candidates for total knee replacement. Starting in the 1990s, however, the age range was broadened to include more patients older than 75, who are likely to have other health issues, and patients younger than 60, who are generally more physically active and whose implants will probably be exposed to greater mechanical stress. Total knee replacement is highly successful in relieving pain and restoring joint function , according to the AAOS. A knee replacement lasts at least 20 years in about 80 percent of those who get them, the AAOS reports. Women account for about 60% of knee joint replacement surgeries and in 2006, an artificial knee designed specifically for women became available.

The largest joint in the body, the knee joint is formed where the lower part of the thigh bone (femur) joins the upper part of the shin bone (tibia) and the knee cap (patella). Shock-absorbing cartilage covers the surfaces where these three bones touch. In a standard total knee replacement, the damaged areas of the thigh bone, shin bone, and knee cap are removed and replaced with prostheses. The ends of the remaining bones are smoothed and reshaped to accommodate the prostheses. Pieces of the artificial knee are typically held in place with bone cement. The most commonly used FDA-approved joint prostheses for knees are made of metal and plastic. The metal is usually titanium or a mixture of cobalt and chromium. The plastic is a high-density polyethylene. Although the metal in a prosthesis is highly polished and the polyethylene is intended to be wear-resistant, the daily rubbing of these surfaces against each other during normal movement creates tiny particles of debris. After many years, these particles may damage the surrounding bone, loosen the prosthesis, and require another knee joint replacement. In an effort to solve the wear problem of metal-on-polyethylene in the hip joint, manufacturers have produced hip prostheses with three other kinds of surfaces: metal-on-metal, ceramic-on-polyethylene, and ceramic-on-ceramic. Unlike the clay ceramic used in pottery, the ceramic used in knee joint replacements is made from aluminum or zirconium that is chemically combined with oxygen for strength and durability. Metal-on-metal and ceramic hip prostheses are decades old, but modern materials, designs, and manufacturing methods have improved upon the earlier versions.

The surgery is performed by an orthopedic surgeon who makes a cut over the affected knee. The knee cap (patella) is moved out of the way, and the ends of the thigh bone (femur) and shin bone (tibia) are cut to fit the prosthesis. The undersurface of the knee cap is cut to allow the surgeon to place an artificial piece. The two parts of the prosthesis are placed onto the ends of the femur, the tibia, and the undersurface of the patella using a special bone cement. Usually, metal is used on the end of the femur, and plastic is used on the tibia and patella, for the new knee surface. In some cases, a mini-incision may be used to avoid cutting the tendon on the front of the knee. This may allow for faster, less painful recovery, but it has risks because of the difficulty of the surgery and the lack of a clear view for the surgeon. A device called a foley catheter may be inserted during surgery to monitor the function of the kidneys and hydration level. This is usually removed on the second or third day after surgery.

QUESTIONS TO ASK YOUR DOCTOR

• Why am I a candidate for knee joint replacement?
• Are there other options available, including partial replacement?
• What is my expected recovery time?
• What is the latest research on knee joint replacement surgery?

Preparation

The patient should be prepared for a three- to five-day or longer hospital stay. The surgery is done in a hospital while the patient is under general anesthesia . Knee joint replacement surgery usually takes about two hours with another one to two hours in a recovery room while the anesthesia wears off. When choosing a prosthesis, the surgeon will consider many factors, including the patient's age, weight, gender, anatomy, activity level, medical history, and general health.

Aftercare

A knee replacement usually involves three to five days in the hospital. An elderly person may need to spend additional days in the hospital and may also need to spend several weeks recovering in an intermediate care facility. The recovery period depends on a patient's general health, age, and other factors, but many people can resume their normal activities four to eight weeks after surgery. After knee replacement surgery, people can sometimes begin walking a day after surgery although in elderly patients it may take several to a few days before they can begin walking. Some patients, especially elderly, may require a walker or crutches to assist their walking. Total recovery time can take from several months to a year. Physical therapy is an essential part of knee joint replacement surgery recovery. It begins within a few days after surgery and is designed to strengthen the muscles around the artificial joint and help regain motion. Physical therapy usually lasts a few weeks but may take longer, especially in elderly patients.

Complications

Complications following knee joint replacement surgery include:

• Infection—Areas in the incision or around the new joint may become infected, sometimes even years after the surgery. Minor infections are usually treated with antibiotics. Deep or severe infections may require another surgery to treat the infection or replace the joint.
• Blood clots—Clots may form if the patient's blood moves too slowly. Symptoms include pain and swelling in the knee. Treatment may include blood thinning drugs, or special stockings, exercises, or boots that make the blood move faster.
• Loosening—The new joint may become loose and cause pain. If the problem is severe, it may require another surgery.
• Dislocation—In some cases following surgery, the ball of the replacement joint can come out of its socket. In most cases, it can be corrected by wearing a knee brace. In severe cases, surgery may be needed.
• Wear—All joint replacements will incur wear over time and use. Too much wear can cause the artificial joint to become loose or wear thin. Surgery may be required to replace part or all of the artificial joint.
• Nerve and blood vessel injury—Nerves and blood vessels near the replacement joint can be damage during surgery. The damage usually heals over time but sometimes additional surgery may be required.

Results

The results of a total knee replacement are often excellent. The operation relieves pain in most patients, and most need no help walking after recovery. Most prostheses last 10 to 15 years, some as long as 20 years, before loosening and needing another surgery, according to NIAMS. Ninety percent of those who have total knee replacement report fast pain relief, improved mobility, and better quality of life, according to a panel of independent experts. The panel was convened at a conference in 2003 sponsored by the National Institutes of Health (NIH) and cosponsored by the FDA and other federal organizations. The panel concluded that, overall, total knee replacement surgery is a safe, very successful, and relatively low-risk treatment for decreasing pain and increasing mobility in people who are not helped by nonsurgical treatments. Follow-up studies showed that revision surgery was needed in 10 percent of knee replacements after 10 years, and in 20 percent after 20 years, according to the panel. As artificial knee joints and surgical techniques to implant them continue to evolve, the medical community expects researchers will develop knee joint replacements that cause fewer problems, last longer, and move more like a healthy natural joint.

KEY TERMS

Cartilage —A tough, elastic material that covers the ends of the bones where they meet to form a joint, such as the knee.

Neuropathy —A disease of the nervous system.

Orthopedic surgeon —A doctor who specializes in the treatment, including surgery, of bones, joints, and soft tissues such as ligaments, tendons, and muscles.

Osteoarthritis —A form of arthritis characterized by gradual loss of cartilage of the joints that is more common as people age.

Peripheral vascular disease —Hardening of the arteries, caused by a buildup of plaque.

Prosthesis —An artificial body part, such as a plastic and/or metal knee joint.

Rheumatoid arthritis —A disease in which the immune system is believed to attack the linings of the joints, causing inflammation.

Rheumatologist —A doctor who specializes in arthritis and related disorders.

Tendon —The flexible but strong connective tissue that attaches muscles to bones.

Caregiver concerns

The surgery is performed by an orthopedic surgeon who is assisted by an orthopedic or surgical nurse. An anesthesiologist will administer the anesthesia and monitor the process. A physical therapist will usually conduct the physical therapy along with assistants. If the knee problem was due to rheumatoid arthritis, the patient may be monitored by a rheumatologist who specializes in non-surgical treatment before and after the replacement surgery.

Resources

BOOKS

Brugioni, Daniel J., and Jeff Falkel. Total Knee Replacement and Rehabilitation: The Knee Owner's Manual Alameda, CA: Hunter House, 2004.

Fairview Health Services. Your Guide to Total Knee Replacement Minneapolis: Fairview Press, 2007.

Scott, Richard D. Revision Total Knee Arthroplasty New York: Springer, 2005.

PERIODICALS

Lucas, Brian. “Preparing Patients for Hip and Knee Replacement Surgery.” Nursing Standard (September 19, 2007): 50(8).

McNamara, Damian. “Total Knee Replacement Falls Short of Expectations.” Family Practice News(January 15, 2008): 33.

Temple, Jenny. “Care of Patients Undergoing Knee Replacement Surgery.” Nursing Standard (August 9, 2006): 48(10).

Wachter, Kerri. “What Do Patients Ask About Knee Replacement?” Internal Medicine News(April 1, 2007): 27.

Yeager, Selene. “Female-Friendly Knees.” Prevention(September 2006): 48.

ORGANIZATIONS

American Academy of Orthopaedic Surgeons, 6300 North River Road, Rosemont, IL, 60018–4262, (847) 823 7186, (800) 824-2663, (847) 823-8125, pemr@aaos.org, http://www.aaos.org.

American College of Rheumatology, 1800 Century Place, Suite 250, Atlanta, GA, 30345-4300, (404) 633-3777, (404) 633-1870, http://www.rheumatology.org.

American Physical Therapy Association, 1111 N. Fairfax St., Alexandria, VA, 22314-1488, (703) 684-2782, (800) 999-2782, (703) 684-7343, consumer@apta.org, http://www.apta.org.

Arthritis Society, 393 University Ave, Suite 1700, Toronto, ON, Canada, M5G 1E6, (416) 979-7228, (800) 321 1433, (416) 979-8366, info@arthritis.ca, http://www.arthritis.ca.

Australian Rheumatology Association, 145 Macquarie St., Sydney, NSW, Australia, 2000, 02 9256 5458, 02 9256 9692, robynm@racp.edu.au, http://www.rheumatology.org.au.

Canadian Institute of Musculoskeletal Health and Arthritis, 160 Elgin St., 9th Floor, #4809A, Ottawa, ON, Canada, K1A 0W9, (613) 957-8678, imha@cihr-irsc.gc.ca, http://www.cihr-irsc.gc.ca.

National Institute of Arthritis and Musculoskeletal and Skin Diseases, 1 AMS Circle, Bethesda, MD, 20892 3675, (301) 495-4484, (877) 226-4267, (301) 718-6366, niamsinfo@mail.nih.gov, http://www.niams.nih.gov.

Ken R. Wells