If you play hard on surgically replaced knees or hips, is there a price you will eventually pay?

When a person with an arthritic hip or knee has the joint surgically replaced, doctors provide a long list of prohibited activities. Running and other bone-jarring pastimes like soccer and basketball are out, because they can cause the implant to deteriorate far too quickly and put a patient back on the operating table to get the join replaced again. This procedure is called a "revision" and is a far more serious operation.

Patients are fully aware of the banned activities and the potential consequences. But there seem to be two kinds of joint replacement patients in this world.

Those who follow doctor's orders.

And those who don't.

Bill Unsworth, 58, follows doctor's orders. He described his approach on the GeezerJock Web site, for which he wrote "The Hip Replacement Diaries," a chronicle of his second hip replacement. Now the offensive coordinator for Saginaw Valley State University's football team, Unsworth has resigned himself to giving up certain sports. "There are some things like going skiing that I just can't do," he said.

But that doesn't mean he has abandoned exercise. The coach still swims four times a week, rides his bike regularly, and, remarkably, can bench press 225 pounds 11 times.

On the other hand, there's 71-year-old Fred Rosen, who owns Sam's Wines & Liquors in Chicago. With two surgically replaced knees, he still plays full-court basketball several times a week. With every trip down the floor and every jump shot, Rosen knows he may be speeding down the road to a revision. He says that other men with arthritic knees ask him about his artificial joints all the time. "I tell them, if you're a nut, you do what I do," Rosen said. "If you're a sensible guy, you don't."

Bo Jackson showed a wide audience what athletic feats were possible after hip replacement surgery, which he had in 1992. The next year, he hit a home run for the Chicago White Sox in his first major league at-bat after the operation.

But even an athlete like Jackson couldn't keep it up. After hitting .279 and belting 13 home runs in 1994, he needed a revision of his metallic hip. His days as a professional athlete were over. He was 31 years old.

But doctors say there is reason for optimism in the 15 years since Jackson's initial joint replacement, which is good news for the 250,000 Americans who have hip replacements and the 500,000 who have knee replacements annually.

Those figures are expected to rise with the aging of the Baby Boomers, who have abused their knees and hips with obesity at one end of the spectrum and with marathons at the other. Between 1998 and 2004, the number of hip replacements increased 46 percent. In the same time frame, the number of knee replacements jumped 80 percent, according to the American Academy of Orthopaedic Surgeons.

One reason that the number of surgeries is increasing is that the implants themselves are getting better and more precise. For example, Stryker Corp. and Zimmer Holdings, two of the world's biggest implant manufacturers, have introduced knee implants that can be formed to fit the specific shape of an individual's knee.

Additionally, new material, such as titanium or other metals coated with ceramics, reduce wear. Newer surfaces, which include "contoured" shapes and thinner profiles are giving doctors hope that some implants could last a lifetime. "They have these newer surfaces that last much longer," explained Dr. Jason Koh, an associate professor of orthopedic surgery at Northwestern Memorial Hospital in Chicago. "I kind of compare it to just how a car from 30 years ago would rust through pretty quickly. Implants today are built to last a lot longer."

Another former White Sox slugger, Albert Belle, is pushing the envelope in a new surgical technique that does not involve cutting away and replacing the bone. Belle's career was cut short by an arthritic hip that eventually made it painful for him to play even a low-stress sport like golf.

To repair Belle's hip earlier this year, his surgeon, Dr. Mitchell Sheinkop, used a technique called "hip resurfacing" that involved reshaping the head of the femur (rather than sawing through bone) and capping it with a smooth metal ball. Cyclist Floyd Landis underwent a similar procedure.

Sheinkop, director of the joint replacement program at the Neurologic & Orthopedic Institute of Chicago, said the technique allows for a quicker recovery time than total hip replacement, which involves cutting away the worn bone, inserting a metal stem in the femur and replacing the hip socket. Sheinkop believes hip-resurfacing has much potential for patients under the age of 55 who are active.

There are Masters athletes who have had joint replacements and who follow doctor's orders closely who are still competing at a high level. Barbara Dunbar, a Masters swimmer who lives in La Jolla, Calif., suffered from a congenital hip condition and by the time she was in her early 50s she was walking with the aid of forearm crutches.

She had a hip replacement at age 53. She quickly returned to swimming, a non-weight bearing exercise highly recommended for joint replacement patients. She says she is generally meticulous about following doctor's orders, down to modifying her flip turns in the pool so that she won't bend her torso past 90 degrees. But shortly after the operation, she set an age-group record in the one-hour postal swim. "I probably shouldn't have done it, but I did it anyway," she said.

Now 58, Dunbar swims five times a week. She estimates her training swims average 4,000 yards. "My legs are, surprisingly, still getting a little stronger," she says.

John Mitchell got the bad news that his right hip was decaying when he was just 36 years old. It was a shock to the one-time college swimmer from Evanston, Ill.; he thought the pain was from his Ironman training. The doctor recommended a hip replacement, and Mitchell bore the pain for six years, waiting for the Food and Drug Administration to approve a new hip procedure designed to last longer and perform better.

Now, 47, Mitchell walks with a ceramic coated titanium hip and says that only his close friends know he has an artificial joint. With three kids under five years old, he wants the hip to last, so he avoids running -- although he occasionally plays doubles tennis.

He does swim and bike regularly, and he remains a strong enough cyclist to do a charity century ride every summer. He also competes in triathlons, handling the swim and bike legs and leaving the running to his wife. He remains a strong swimmer. "When people pass me during the bike (part of a triathlon), I say to myself, 'Well at least I kicked your ass on the swim,'" he said wryly.

It seems that no matter how careful a hip replacement patient is, revision is always a looming possibility. Barbara Lefleur of Tenafly, N.J., has given up singles tennis but she still plays doubles on two artificial hips. She plays well enough that she and her partner qualified for this summer's National Senior Games in Louisville, Ky.

She doesn't play as often as she used to, but she's determined to keep playing no matter the consequences. "Some people are using their hips to walk to the corner," she said. "That's not for me. As long as I can move without pain, I'm going to move. I fully expect I'll need a revision, sooner than later."

Like Lefleur, Milo Karhu, a 68-year-old who lives in The Villages, Fla., still plays doubles, although his sport is pickleball. Despite playing with a surgically-replaced hip, he was one of the favorites in the 60-plus bracket in The Villages GeezerJock Pickleball Championships.

Karhu, a former school principal, gave up softball and racquetball after his hip replacement in 1999. He still plays doubles pickleball, a game similar to paddle tennis but using a plastic ball like a Wiffleball, almost every day. He said his doctors permitted and even encouraged this exercise. Nonetheless, Karhu underwent a revision to the hip replacement last year.

Now he's back on the court and playing as often as ever. "I feel so lucky I'm still able to do this kind of stuff," Karhu said. "If this were 20 or 30 years ago, I'd probably be in a wheelchair right now."

There are other Masters athletes who are pushing their luck by completely ignoring doctor's orders, and they know it. Rosen, who has been involved with sports all his life and played college football and basketball at the University of Denver, just can't give up basketball. "I've been warned by my surgeon that a replacement of a replacement is really serious," he said. "I'm gambling that I'll be O.K."

He can't stop playing; sports are where his friends are. "That how I am," he said. "I don't play tennis. I don't play golf. I'm at the gym every day. There are games going on, and I usually cover a guy in his 50s or 60s. We have a noncombatant clause."

If a revision comes, and the worst comes along with it, Rosen is ready to learn a new sport. "I'm already planning on playing wheelchair basketball," he said, only half joking.

George Clamp, 57, says he's finally ready to give up soccer now that he has two metal knees. Originally from Birmingham, England, Clamp has played soccer since he was six years old. He played semiprofessionally in the United Kingdom, and since coming to the States in 1982, he has played competitive soccer. He doesn't want to give it up. "Anybody who loves soccer, it's something you want to keep playing until you drop dead on the field," he said.

He planned to give up soccer after his first knee replacement six years ago. "All of a sudden the knee, after six months, is fantastic," he recalled. "Now it wasn't my plan to go back and play, but I played another five years."

But soccer injuries and his trade of laying tile have combined to damage his knees and end his soccer career. Maybe. "Never say never," he said.

Maybe Clamp should hear Barry Clemens' cautionary tale. Clemens flouted doctor's orders, playing basketball on a surgically-repaired hip for years. "I did fine for a long time, but it's created a problem somewhere else (in my body)," the 64-year-old former NBA player said.

Clemens, who is a financial planner, has always had a high threshold of pain. He played for three months on a femur with a hairline fracture when he was in the pros. Later, with his hip deteriorating, he readied himself for the pain of the pounding in Masters basketball games by swallowing handfuls of over-the-counter painkillers. "One day I took 32 Advil, just to block out the pain out for an hour, and it didn't even do that. It helped a little bit."

When he finally had his hip replacement surgery, he needed no morphine after the surgery. "I was in so much less pain after the surgery that I didn't need the painkillers," he said. "The nurse looked at me like I had four eyes." Clemens remembers the instructions for activity after the surgery. "Bike, swim, play a little golf. I said, 'O.K., I hear you,'" he said.

Feeling no pain in his hip, he gradually returned to full court basketball. He played in top notch Masters tournaments all over the world. Going up against other former NBA players, he remembers scoring 35 points in one age-group championship game on his surgically replaced hip.

Now, however, Clemens is wracked by almost unbearable back pain. He blames continuing to play on his metallic hip for this new pain. "I said, 'I'll take my chances,' but basically I should have taken their advice," he said.