Joint Replacement:
An Inside Look

Turn on the TV and there is golf legend Jack Nicklaus extolling the virtues of his hip replacement. Still competing on the links, Nicklaus is among the growing number of people in the United States each year who have a hip joint replaced. So is rock star Eddie Van Halen, who was 43 when he had his hip replaced in 1999, the same year as Nicklaus.

Cases like these are laying to rest the stereotype that only the aged and the inactive receive hip replacements. The same holds true for those who have knee joints replaced.

The American Academy of Orthopaedic Surgeons (AAOS) calls total hip replacement an orthopedic success story, "enabling hundreds of thousands of people to live fuller, more active lives." In 2001, about 165,000 hip joints were replaced in U.S. hospitals, according to the National Center for Health Statistics. The same year, 326,000 knees were replaced. Total knee replacement is "highly successful in relieving pain and restoring joint function," says the AAOS. And a hip or knee replacement lasts at least 20 years in about 80 percent of those who get them.

But despite their success, hip and knee joint replacements still have drawbacks. There may be complications. They don't always last a lifetime and when they fail, surgery may be needed.

As artificial joints and surgical techniques to implant them continue to evolve, the medical community and patients hold out hope for joint replacements that cause fewer problems, last longer, and move more like a healthy natural joint.

What is Joint Replacement?

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 hip or 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 Food and Drug Administration.

Why Joint Replacement?

The most common reason for having a hip or 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, is not limited to older people. Although it most commonly affects people over age 45, 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 hip or knee joint replacement. This chronic inflammation of the joint lining causes pain, stiffness, and swelling. The inflamed lining can invade and damage bone and cartilage. Rheumatoid arthritis generally starts in middle age, but can also affect children and young adults.

Loss of bone caused by poor blood supply (avascular necrosis), which led to Van Halen's hip replacement, and bone tumors may be other reasons for joint replacement.

Hip Replacement Surgery

The hip joint is a ball and socket, allowing a wide range of motion. The ball of the joint, the top of the thighbone (femoral head), moves within the hollow socket (acetabulum) of the pelvis. A layer of cartilage allows the ball to glide smoothly inside the socket.

In total hip replacement, the surgeon cuts away the ball part of the joint, replacing it with a ball attached to a stem that is wedged into a hollowed-out space in the thighbone. Damaged cartilage and bone are removed from the socket and a cup-like component is inserted into the socket.

Hip replacements may be cemented or uncemented. If cemented, the hip parts are held in place with a fast-curing "bone cement" made from a type of polymer. If uncemented, the joint components are specially made to either press into the bone for a tight fit (press-fit) or to allow new bone to grow into the porous surface of the implant, holding it in place (biological fixation).

Hip Resurfacing

An alternative to total hip replacement is an operation called hip resurfacing. Unlike the prostheses used in total hip replacement, which are made to replace the femoral head, resurfacing prosthesis designs allow the head to be preserved and reshaped. The resurfaced bone is then capped with a metal prosthesis. Like total hip replacement, the socket is fitted with a prosthesis.

In the United States, hip resurfacing is being conducted only in FDA-approved clinical studies. It is necessary for each manufacturer of a hip resurfacing device to collect clinical data on its resurfacing design. The data collected in these studies will be used to demonstrate whether each hip resurfacing design is safe and effective for market approval in the United States. Presently, no manufacturer has obtained FDA approval to market its hip resurfacing design.

Not everyone is a candidate for resurfacing; the femoral head may be too damaged to hold the resurfacing component. "Good bone stock is required," says Michael Mont, M.D., director of the Center for Joint Preservation and Reconstruction at Sinai Hospital in Baltimore.

James Puglisi considers himself fortunate to have good bone stock. Puglisi was 47 when he began limping because of a burning, aching pain in his hip that spread through his leg and into his knee and ankle. For this marathon runner and cyclist, just walking and standing became painful, and sometimes the pain was so intense that it would wake him up during the night.

Puglisi was diagnosed with osteoarthritis, brought on by an abnormally formed hip joint. He was advised by his orthopedic surgeon to wait as long as possible before getting a total hip replacement because it might wear out with his active lifestyle and require one or more revisions.

Revision surgery, which replaces both artificial parts and damaged bone, is more difficult than first-time surgery, says NIAMS. The outcome is generally not as good because bone is not as strong as when first operated on and the supporting ligaments may be damaged.

"But the pain was getting to the point where I needed to do something," says Puglisi.

Puglisi flew from his home in Amherst, N.Y., to Baltimore to take part in a study on hip resurfacing. Mont performed Puglisi's resurfacing operation in March 2003 and Puglisi returned home after a four-day stay at Sinai Hospital. Gradually putting more weight on his new hip, Puglisi was able to be full weight-bearing (walking without a cane or crutches) after three months. Now pain-free, the 50-year-old is back to cycling 200 miles a week and anticipates running again soon. "I'm so happy with the results," he says. "I had forgotten what it was like to have a pain-free life, and now I have it back. It feels as normal as my other hip."

Puglisi notes that different surgeons may have different recommendations. Another surgeon who saw Puglisi's X-rays told him he shouldn't run again. "But Dr. Mont was OK with it as long as I waited at least six months after surgery," says Puglisi. "He just told me I couldn't bungee jump or parachute!"

Mont advises the six-month waiting period to give a patient time to build strong muscles. He also says he doesn't "totally condone heavy sporting activities" after resurfacing. "You do it at your own risk," he says, adding that if the resurfaced hip ever fails, it can be converted to a total hip replacement.

Current hip resurfacing technology is too new to know how long the resurfaced hip will last. Puglisi has volunteered to return to Sinai Hospital for an annual checkup for the next 10 years to help clinical investigators gather long-term data on resurfaced hips.

Knee Replacement Surgery

The largest joint in the body, the knee joint is formed where the lower part of the thighbone (femur) joins the upper part of the shinbone (tibia) and the kneecap (patella). Shock-absorbing cartilage covers the surfaces where these three bones touch.

In a standard total knee replacement, the damaged areas of the thighbone, shinbone and kneecap 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.

A knee replacement usually involves three to four days in the hospital. 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.

"While a knee replacement can dramatically improve the quality of life for a person with debilitating knee pain, it is major surgery," says Gerard Engh, M.D., director of knee research at Anderson Orthopaedic Research Institute in Alexandria, Va. "We usually recommend total knee replacements and partial knee replacements after other less invasive treatments have been attempted."

But most who opt for knee joint replacement are generally happy with the results. 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 December 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.

Where the FDA Fits In

Artificial joints are medical devices, which must be cleared or approved by the FDA before they can be marketed in the United States. In addition, FDA permission is required before a company can test a new or redesigned prosthesis in human studies. The data gathered in these studies, which take place in specific hospitals, may then be used to support a company's application for marketing its prosthesis to surgeons and hospitals throughout the United States.

What does the agency look for before clearing a prosthesis for marketing? "It has to be proven safe and effective," says Barbara Zimmerman, chief of the FDA's orthopedic devices branch. "FDA assures safety and effectiveness using different means depending on the risks of a particular device and the technology that it presents."

For devices with a history of safe and effective use, frequently those using established technology, the FDA relies on a set of general controls to determine which devices can be marketed, says Zimmerman. "These general controls are augmented with special controls such as standards or standard test methods.

"For devices involving new uses or advanced technology, FDA often requires that a particular device be demonstrated to be safe and effective through clinical trials," she says.

The Risks of Replacement

Like any surgery, hip and knee joint replacement carries certain life-threatening risks, such as infection, blood clots and complications from anesthesia. Other complications include nerve damage, dislocation or breakage after surgery, and wearing out or loosening of the joint over time. After hip replacement surgery, one leg may be shorter than the other.

Infection is an ongoing risk for people with joint replacements. Not only can it occur in the hospital, but it can happen years later if bacteria travel through the bloodstream to the replacement area.

In the rare case that an infection spreads to the new joint and does not clear up with antibiotic treatment, the joint must be replaced. This usually requires two surgeries--one to remove the infected joint and another surgery later to insert the new joint. Between surgeries, the infection is treated with antibiotics.

In 2001, the FDA approved a temporary artificial hip for people with hip joint infection. The temporary hip, called Prostalac, can be inserted and left in place for about three months after the infected hip is removed. It consists of a metal stem and ball that fits into the thighbone, a plastic cup that attaches to the hipbone, and a bone cement that contains antibiotics. The antibiotics in the cement, along with oral antibiotics taken by the patient, help to treat the infection. The temporary hip allows a person some movement while healing.

The Wear Problem

The most commonly used FDA-approved joint prostheses for knees and hips 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 movements creates tiny particles of debris. After many years, these wear particles may damage the surrounding bone, loosen the prosthesis, and require another knee or hip joint replacement.

"The 'Achilles tendon' of any artificial joint over the long term is wear," says Anderson Orthopaedic's Engh. "Any time you have parts moving against each other, there has to be wear."

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 hip joint replacements is made from aluminum or zirconium 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 earlier versions, says Engh. He cautions that, although modern investigational products have shown good wear in mechanical simulations in the laboratory, it's how well they work in people over the long term that is the real test. "Very often it's best to select an implant that's been on the market for a while rather than something that's brand new," says Engh.

A few metal-on-metal and ceramic-on-ceramic hip prostheses are FDA-approved for use in the general population; others are approved only for use in carefully controlled studies. However, a large number of ceramic-on-polyethylene prostheses are available for use in the general population.

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, says A. Seth Greenwald, D.Phil., director of orthopaedic research and education at the Lutheran Hospital in Cleveland, part of the Cleveland Clinic Health System. The device's performance record and the surgeon's own experience with the device also will be considered.

Surgical Skill

Choosing the appropriate prosthesis is only one part of the equation for successful hip or knee joint replacement. "The most important factor in joint replacement success is the surgeon," says Greenwald. "The first question I'd ask the surgeon is, 'How many have you done and what are your complications?'"

Jonathan Garino, M.D., agrees. "There are a number of good devices out there," says Garino, an orthopedic surgeon with the University of Pennsylvania Health System. "But even if you have the best technology in the world, it has to be implanted correctly." It falls to the surgeon to put the device in right, but it falls to the patient to take care of the new joint, says Garino. Regular exercise is important, but high-impact activities, such as running and jumping, generally are discouraged.

The independent panel convened by the NIH in December 2003 to study total knee replacements also concluded that proper surgical technique was one of the most important factors leading to successful knee replacement. Studies have found that the more knee replacements a surgeon performs, the lower the rates of complication, according to the panel. Similarly, complication rates fall in hospitals with increasing numbers of operations performed.

Surgical Techniques

While prosthesis makers are changing designs, materials, and manufacturing methods to try to lengthen the life of artificial knees and hips, surgeons are refining techniques or developing new ones to try to improve the outcomes. Doing surgery through smaller incisions and performing less radical surgeries are among these efforts.

People are seeking minimal-incision knee and hip replacement surgery, says Engh. Instead of the traditional 6- to 12-inch-long incision used in a standard total knee replacement, some surgeons are performing the surgery through a 4- to 5-inch incision. And instead of the typical 10- to 12-inch incision in a total hip replacement, surgeons are operating through one 4-inch cut or two 2-inch cuts.

"The [minimal-incision surgery] technique minimizes trauma to muscles, tissue and tendons and has less bleeding during surgery," says Garino. Patients have less pain after surgery, enabling them to walk with full weight sooner. The hospital stay is usually reduced as well.

"There are many advantages as long as we don't compromise our ability to put the implants in correctly," says Engh, adding that minimal-incision surgery is a more difficult operation to perform. "If you assemble a model ship on a desktop, it's easier to do, but if you try to assemble it within a bottle it is technically more difficult," he says. The technical difficulty also adds to the operating time. "The longer a patient is in surgery, the higher the risk of infection," says Engh.

Not all patients are candidates for minimal-incision surgery. People who are obese, have had previous hip or knee surgery, or those with unusual anatomy may be excluded, says Garino.

Minimally invasive surgery is another option for some patients. At Sinai Hospital, Mont performs a minimally invasive total knee replacement through an incision of 4 to 6 inches, bending the joint through the opening to expose different parts of it to work on. In a standard knee replacement, the entire joint is visible through a longer incision. Mont uses cutting procedures, leg positionings, and techniques that do not involve dislocating parts of the knee as in traditional replacement.

Even as researchers and surgeons continue to offer more options in prostheses and surgical procedures, Garino says the current technology is hard to beat. A hip or knee replacement is likely to last 20 years, he says. "The average patient takes a million steps a year. I challenge you to go home and find something in your house that you use a million times a year that has lasted for 20 years with no maintenance."

What to Ask the Surgeon

Here are some questions to ask your surgeon about joint replacement: