Smarter hip and knee repair

New artificial joints can last longer—but are also oversold

Consumer Reports on Health: February 2009

More Americans than ever are walking around with artificial hips and knees, and aging baby boomers are leading the way. That's partly because excess weight is fraying their joints earlier. Between 2000 and 2006, knee replacements shot up by 65 percent, and a growing number of patients were under age 65, according to the National Center for Health Statistics. And the numbers may grow. Nearly one in two adults—and two-thirds of obese adults—will develop painful knee arthritis, researchers estimate.

Hip and knee replacements get high marks for relieving arthritis pain. Though the procedures can have serious complications and don't always restore perfect mobility, more than 80 percent of people said they were "very" or "completely" satisfied with their new joints, according to a Consumer Reports survey of 1,000 patients who had the surgery between 2000 and 2004. And since then, advances in pain control and rehabilitation have sped recovery.

But the increase in younger patients, who will eventually outlive their artificial joints, poses challenges. Manufacturers have responded with new implants that last longer in the laboratory than traditional ones, but none of them has been tested long enough to know how they will perform beyond 10 or 20 years in real life. Yet the implants, as well as several controversial surgical procedures, have been heavily advertised to consumers and rapidly accepted into practice. "Physicians feel that if they don't jump on this technology bandwagon, they'll be left behind the rest of the pack," says Matthew Kraay, M.D., professor of orthopaedic surgery at the Case Western Reserve University School of Medicine in Cleveland. "They don't have an opportunity to wait for the peer-reviewed result."

But early reports are trickling in. The following guide will help you weigh the pros and cons of current options in hip and knee surgery.

When it's time to replace a damaged joint

Waiting until arthritis damage is severe can make surgery harder and full recovery less likely. Check the list below to see if it's time to talk with an orthopedic surgeon about joint replacement.

Medication doesn't relieve the pain or produces unacceptable side effects.

The pain makes it hard to sleep.

You have trouble with routine movement, such as bathing, climbing stairs, or getting out of a chair.

The pain interferes with your lifestyle by, for example, making it difficult to exercise, shop, or visit friends.

Why good joints go bad

An artificial hip gets anchored into a hollowed-out portion of the thighbone.

The most common cause of hip and knee damage is osteoarthritis—the erosion of cartilage between the joints that allows adjoining bones to rub together. (Joints damaged by rheumatoid arthritis, a less common but more serious disorder, can be replaced as necessary when medical treatment has failed.) Often, you can delay or even eliminate the need for joint replacement by the judicious use of over-the-counter pain relievers, losing excess weight, and by doing regular low-impact exercises such as tai chi and water workouts. To learn what exercises help relieve arthritis pain, speak with a physical therapist or contact the Arthritis Foundation.

But when the damage is advanced, joint replacement becomes a good option. In knee replacement, surgeons remove damaged portions of the thighbone, shinbone, or kneecap and insert artificial parts, generally using cement to help keep them in place. In hip replacement, they cut off the head of the thighbone, or femur, and hollow out its shaft. Then they insert a new hip socket and a new femoral head, anchored by a stem that's wedged into the shaft, usually without cement. In either operation, the parts are usually made of metal and polyethylene,a plastic. They can last 20 years, but they wear out earlier in younger, heavier, and more active people.

The most common reason hip and knee implants fail is loosening. As metal and plastic rub together, the friction wears away the surfaces, creating tiny plastic particles around the joint. The body attempts to remove those particles but in the process removes bone as well, causing the implant to loosen. The joint then has to be replaced, a procedure known as revision surgery, which is usually less successful than the original operation because of the bone loss.

New parts for old bones

An artificial knee made of metal and polyethylene.
Photo: Journal of Orthopaedics

Manufacturers have addressed the loosening problem by developing new devices. But each has drawbacks. Joshua Jacobs, M.D., chairman of the orthopaedic surgery department at Rush University Medical Center in Chicago, says that many patients base their choice on advertising. Instead, he advises, "Find a physician who is knowledgeable about all the issues, and make a collaborative decision." The first device described below is available for knees and hips; the other two for hips only.

Metal on highly cross-linked polyethylene
Plus: This new plastic wears substantially less than conventional polyethylene.
Minus: It has a shorter track record and might be more prone to fracture.
Recommendation: Paired with metal in the hip, it offers durability with the fewest side effects, making it the best choice for most people. But because the knee puts greater demand on the joint, and thus may increase the risk of fracture, our consultants still generally recommend metal on conventional polyethylene for knee replacements.

Metal on metal
Plus: It wears less than metal on plastic, and offers a larger femoral head, reducing the chance of dislodgment.
Minus: It releases metal particles into the bloodstream that have unknown effects on the body and are particularly worrisome in women of childbearing age. Moreover, a few patients have developed allergies to the metal debris.
Recommendation: This kind of device might make sense for young men in need of hip replacement whose work involves heavy labor, which increases the risks of joint dislocation and wear.

Ceramic on ceramic
Plus: It's likely to wear out the slowest.
Minus: It poses a rare but serious risk of chipping or breaking. Moreover, up to 7 percent of patients have complained of squeaky ceramic hips.
Recommendation: This might be an option for patients who need to get many decades out of their hip, such as very young men, or women of childbearing age.

Minimally invasive surgey

Some surgeons now use a technique called minimally invasive surgery, which might limit damage to muscle and tissue. The potential advantages are faster recovery and reduced pain—but at the cost of longer operative time and a higher risk of surgical errors, including incorrect implant positioning, nerve injury, and bone fracture. The benefits of the procedure are still being debated, but marketing claims have fueled patient demand. "Many surgeons feel they need to offer it or they'll lose patients to someone else," says Mark Pagnano, M.D., an associate professor of orthopaedic surgery at the Mayo Clinic. "But the scientific evidence that this technique makes a substantial difference is lacking."

In fact, improvements in pain control and rehabilitation appear to speed recovery in hip-replacement patients whether they have small or conventional incisions, according to a 2007 study published in the Journal of Bone and Joint Surgery. Physicians note the same effect in knee patients.

Many surgeons now use "mini" cuts that are significantly smaller than traditional incisions but large enough for them to view the operating field. Our consultants support that approach because it provides most of the benefits of minimally invasive surgery without compromising safety. But they note that large-boned patients still require larger incisions, as do those who are overweight, have a joint deformity, or have had prior surgery on the joint.

Hip resurfacing

Aimed at younger patients who want to delay total hip replacement, this procedure removes only the damaged joint surfaces. The socket is replaced with a metal cup and the femoral head is shaved down and covered by a metal cap anchored by a short stem. That preserves more of the thighbone, making future revision surgery easier.

"Patients read marketing materials and want this procedure," says John Callaghan, M.D., second vice president of the American Academy of Orthopaedic Surgeons. "But the appeal of preserving bone can lead to false expectations."

Women who had resurfacing are twice as likely to need early revision than those receiving regular hip implants, chiefly due to femoral neck fractures, according to a 2008 review by the Royal College of Surgeons of England. Women might be at higher risk for such fractures because their bones are smaller and weaken at menopause.

Additional concerns include the complexity of the operation and metal-on-metal debris. Some surgeons avoid the procedure altogether, others recommend it only for younger men, and some propose it for strong-boned patients regardless of gender. But most agree that resurfacing is not advisable in patients who are likely to have weak bones—such as postmenopausal women, people over age 65, or those who score poorly on bone-density tests.

Partial knee replacement

In this procedure surgeons replace only the eroded side of the knee. Compared with total knee replacement, it offers a smaller incision, faster recovery, and superior function. Moreover, it might buy patients 10 to 15 years before they need total knee replacement.

But the operation isn't as durable or predictable as total knee replacement. In the same British study, which looked at more than 80,000 knee patients, early revision rates were twice as high for those who had partial knee replacement, especially among younger patients. Common reasons for failure include loosening and arthritis in other parts of the knee.

"Partial knees are great in the right person," Kraay says. "But only one in 20 people who need knee replacement are candidates." Patients should have arthritis in only one side of the knee, intact ligaments, and good range of motion. In addition, they can't be very heavy, nor too bowlegged or knock-kneed. Callaghan cautions that, like hip resurfacing, this operation might be overused.

Choosing a surgeon for a new hip or knee

Patients considering hip or knee surgery are often reluctant to ask probing questions of the surgeon, according to a July 2008 study published in the Journal of Bone and Joint Surgery. That can affect the outcome of joint-replacement surgery, which is tied to the surgeon's experience and the aftercare you receive. Below are some questions to ask a surgeon. If you're not satisfied with the response, consider getting a second opinion.

How often in the past year have you performed this operation?
Choose a surgeon who does at least 50 a year. Also ask about the kinds of joints your surgeon uses and about his or her complication rates.

Does the institution do a high volume of joint replacements?
High-volume centers should be more likely to have experienced staff as well as facilities that can minimize the risk of infection. Also ask about the institution's infection rate. Ideally, it should be 1 percent or less.

What are the plans for pain management?
Recovery is fastest in patients who receive regional anesthesia and, for postoperative relief, local anesthetics that are injected around the joint or delivered through a catheter.

What are the plans for rehabilitation?
Look for an institution that gets patients moving soon after surgery. For many people, that reduces the risk of medical complications and hastens recovery.

Latest on glucosamine and chondroitin

These arthritis supplements aren't standing up well to recent scientific scrutiny. Two 2008 studies couldn't find any clear benefits for the pills. That follows other negative findings over the past several years. However, researchers say that the supplements might help certain patients, and other studies are ongoing. If you decide to try the pills, keep a daily record of your symptoms and stop taking the supplements after three months if you see no improvement.

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