If you live long enough - that is, beyond 50 or 60 - chances are one or more of your joints, probably your knees or hips, will become arthritic. And if pain or stiffness begin to seriously limit your ability to enjoy life and perform routine tasks, chances are you'll consider replacing the troublesome joint.

"People with osteoarthritis are relying more and more heavily on surgery," Dr. David T. Felson, a rheumatologist and epidemiologist at Boston University School of Medicine, told me. "The rate of knee replacement is just skyrocketing, out of proportion to increases in arthritic changes seen on X-rays, and replacement surgery is contributing greatly to the rising costs of Medicare."

Between 1979 and 2002, knee replacement surgery rose 800 percent among people 65 and older. Although Dr. Felson described hip replacement as "dynamite" -- highly effective in relieving pain and restoring function -- knee replacement may be far less helpful.

"For 10 to 30 percent of patients, the improvement never comes," Dr. Felson said.

How the Trouble Starts

Osteoarthritis results from wear and tear on the joints. (Rheumatoid arthritis, on the other hand, is an autoimmune disorder.) Some 27 million Americans have life-limiting osteoarthritis, and the numbers are rising as the population gets older and fatter.

"With every step, the force exerted on weight-bearing joints is one and a half times body weight," said Dr. Glen Johnson, who reported on arthritis prevention and treatment at the annual meeting of the National Athletic Trainers' Association in June. "With jogging, the force is increased seven or eight times. Thus, the most effective way to prevent arthritis in knees and hips is to lose weight if you're overweight and to pursue non-impact activities for recreation."

While most people think of osteoarthritis as a breakdown of the cartilage that keeps bones from rubbing together, recent studies have shown it is a far more complicated disease that also involves tissues in and around joints, including bone and marrow. Inflammation can be a contributing factor, and genetics play a role. Three genes have been identified thus far that accelerate the development of arthritis in people who carry them.

Any kind of joint injury or surgery, even if performed arthroscopically, raises the risk that a joint will become arthritic. That is why so many professional and recreational athletes develop arthritis at younger ages.

Still, there are many potential remedies short of surgery to relieve arthritic pain and to preserve -- and perhaps restore -- normal joint function. Even if surgery is needed, it can be postponed for many years with treatments proven to help in well-designed clinical trials.

Artificial joints usually last 10 to 15 years. Delaying surgery is helpful because the earlier in life a joint is replaced, the more likely a subsequent replacement will be needed. And both devices and surgical techniques are constantly being improved; by delaying a joint replacement, you may end up with a simpler operation or more durable device.

Take it from someone who has been there: Joint replacement, especially of the knee, is not a walk in the park. Arduous physical therapy is essential, and recovery can be long and painful. There are limitations after recovery, too, because artificial joints are not as flexible as the ones you were born with.

What Works, What Doesn't

First things first: If you weigh more than you should, do your best to shed those extra pounds. Even a loss of 10 to 15 percent of body weight can make a big difference to weight-bearing joints.

"I can't stress enough how important body weight is," Dr. Johnson said. "With our national crisis of obesity, we'll see more and more arthritis of the knees, ankles, hips and spine."

Stephen Messier, a professor of health and exercise science at Wake Forest University, has shown in a trial among 450 men and women with osteoarthritis that a weight-loss diet combined with a well-designed exercise program can significantly reduce knee pain.

The most helpful exercises are those that strengthen the quadriceps (muscles in the front of the thighs), like leg presses, mini-squats and wall squats, and flexion and extension exercises that restore and preserve range of motion, Dr. Johnson said. Several visits to a physical therapist can help assure that you are doing the exercises correctly.

"The severity of pain is directly correlated with the degree of muscle weakness," Dr. Felson wrote in The New England Journal of Medicine. (If the knee hurts during exercise, he added, then it should be avoided.)

Wearing the right shoes with certain adjustments to the sole and heel, if needed, can help too. Get fitted in a store with expertise in evaluating feet and gait. Are your arches flat? Are you bow-legged or knock-kneed? Wedges specifically designed for you can help take stress off arthritic knees and hips.

Though most experts endorse walking for exercise for its ease, accessibility and low cost, Dr. Johnson instead recommends such non-impact activities as stationary or outdoor cycling, swimming, or working out on an elliptical or rowing machine for cardiovascular fitness. Those who choose to walk, he said, may benefit from runners' shoes designed to dissipate the force on joints.

Bracing an arthritic knee can help, too, especially with an unloader brace that shifts the stress away from the damaged part of the joint. Most patients are unlikely to wear such a brace all the time, Dr. Felson said. Still, knee braces can help arthritis sufferers continue to participate in physical activities, reduce the use of pain medication and postpone the need for surgery.

Pain relievers usually bring only temporary relief, if any. Daily dosing with acetaminophen (the ingredient in Tylenol) should be tried first, experts say, because it is significantly safer than ibuprofen and other nonsteroidal anti-inflammatory drugs, especially for older people.

Well-designed clinical studies have shown no significant relief of arthritic knee pain from supplements of glucosamine and chondroitin sulfate, taken alone or in combination, though Dr. Felson said that if people feel better taking them, he does not discourage the practice.

Nor is there good evidence of benefit from methylsulfonylmethane, SAM-e or acupuncture. Some evidence suggests that osteoporosis drugs may be helpful, though they have not yet been tested for arthritis relief in a randomized clinical trial, Dr. Felson said.

There are also hints of benefit from vitamin K, an essential nutrient found in cruciferous vegetables (broccoli, kale, cabbage and the like), which are good for health in general (unless you take blood thinners).

Doctor-administered treatments include steroid injections every three or four months to control pain and buy time, and injections of a synovial fluid replacement like Synvisc twice a year. In general, though, these are not very effective when arthritis has reached the bone-on-bone stage, Dr. Johnson said.