FRIDAY, March 12 (HealthDay News) -- Patients who get a total knee replacement are usually advised to avoid high-impact sports to preserve their new body part. But a new study suggests sport participation is not only safe -- it may even help people gain better knee function.

''Initially, we though high-impact sports were terrible for the prosthesis," said Dr. Sebastien Parratte, a research collaborator at the Mayo Clinic in Rochester, Minn., and an assistant professor at the Aix-Marseille University Center for Arthritis Surgery at Hospital Sainte-Marguerite in Marseille, France.

"Our eight-year results have shown it is not the case," he said.

He is the lead author of the study, scheduled for presentation Friday at the annual meeting of the American Academy of Orthopaedic Surgeons in New Orleans.

More than a half million total knee replacements are performed annually in the United States, according to the American Academy of Orthopaedic Surgeons. Parratte and his colleagues conducted the study knowing that patients routinely ignore their doctor's advice to take it easy after receiving a knee replacement. In fact, about one of six patients engage in high-impact activities post-implantation, experts say.

Parratte's team followed 535 patients in all. A total of 218 underwent knee replacement and then performed heavy manual labor or engaged in a non-recommended sport, such as high-impact aerobics, football, soccer, baseball, jogging or power lifting. The control group of 317 patients had knee replacement but did not engage in sports that were not recommended.

The researchers evaluated the patients clinically and with X-rays. About eight years after surgery, they found no significant radiological differences and no significant differences in the implant durability between groups.

In fact, the sport group had slightly higher knee function scores than the control group.

A first comparison found that the control group had a 20 percent higher need to repeat the operation because of mechanical failure of the knee (from wear, fracture or loosening) compared to the sport group. But when they took into account other health problems such as obesity or diabetes, the sport group had a 10 percent higher risk of mechanical failure compared to the control group, but the difference wasn't statistically significant.

''The control group was more likely to have high blood pressure, obesity and diabetes," Parratte added.

He said he doesn't know why the sport group's knees held up better.

Still, the study findings are no reason to tell patients with knee replacements to exercise in a high-impact way, said Dr. Christian Christensen, an orthopedic surgeon and head of adult reconstruction at the Lexington Clinic in Lexington, Ky.

"I think it's a good study and certainly a worthwhile one," he said. "Would it encourage me to tell my patients to play football? No way."

More research is needed to evaluate what's happening, he said. It's possible that the people with the best results may be the ones engaging in high-impact sports. "People with the knees that feel great, who have excellent results,'' are perhaps the ones who can engage in the high-impact sports without ill effect, he said.

Another possibility, he said, is that the follow-up may just not be long enough, that ill effects may show up later. Christensen said he'll continue to tell his knee-replacement patients to avoid high-impact sports. "Implants aren't meant to tolerate high-impact sports," he said.

Dr. Benjamin Bengs, another expert, called the new study findings promising. It shows these devices are long-lasting, can lead to lifelong pain relief and excellent functioning and activity in patients, said Bengs, an orthopedic surgeon at Santa Monica-University of California Medical Center and Orthopaedic Hospital.

But more time and study are needed before we completely release people to all high-impact activities, he said.

''One study is not enough to change the recommendations," Parratte agreed. He plans to study the topic further.

More information

To learn more about total knee replacement, visit the American Academy of Orthopaedic Surgeons  .

THURSDAY, March 11 (HealthDay News) -- Long-term use of oral drugs prescribed to keep osteoporosis at bay may be associated with unusual fractures of the thigh bone, two new studies suggest.

The research is not the first to link the drugs, known as bisphosphonates, with unusual fractures. Other research has found pros and cons, with the drugs reducing breast cancer risk but increasing the risk of painful jaw problems.

"Bisphosphonates are a good first start," said study co-author, Dr. Melvin Rosenwasser, a professor of orthopedic surgery at Columbia University College of Physicians and Surgeons in New York City. "Used beyond a certain point, yet to be determined, they may actually be bad."

The research is scheduled for presentation Thursday at the American Academy of Orthopaedic Surgeons' annual meeting in New Orleans, but at least one expert is saying both new studies are flawed.

In his study, Rosenwasser and his colleagues focused on 112 women, all past menopause, who had osteoporosis, which weakens bones, making them more likely to break. Of them, 62 took osteoporosis drugs -- in this case, bisphosphonates -- for four years or more, and 50 took calcium and vitamin D supplements only.

The researchers took bone scans to evaluate the thigh bone structure.

"That allowed us to show changes in the buckling ratio," said Rosenwasser. "That's a fancy way of saying the propensity for the bone to break."

They found that long-term use of the drugs -- at least four years -- was associated with an increase in the buckling ratio, reflecting a higher risk for fracture.

In another study, Dr. Joseph M. Lane, chief of the metabolic bone disease service at the Hospital for Special Surgery and a professor of orthopedic surgery at Weill Cornell Medical College in New York City, and his colleagues compared bone quality in biopsies from patients who had been on bisphosphonates for several years with those not on the drugs.

They looked at bone biopsies taken from the thigh bones of 21 women, all past menopause, who had suffered fractures at the site. Nine had not taken the drugs, while 12 had, for an average of 8.5 years.

"We took bone from close to the fracture site," Lane said. The women on the bisphosphonates, they found, had "old" bone. Normally, Lane said, bone is about 20 percent new, 60 percent middle-age and 20 percent old. "This was 90 percent old bone, suggesting the body is not turning over the bone," Lane said.

When too much of the bone is old bone, Lane said, it lacks the ability to repair microdamage. "What I think is happening is, women keep doing microdamage to the bone," he said. As a result, the unusual fractures of the thigh bone can occur with simple activity, such as climbing stairs.

At least one other expert isn't so sure. Criticizing both studies, Dr. Nelson Watts, director of the University of Cincinnati Bone Health and Osteoporosis Center, said the research has "major flaws" and "major errors in interpretation."

"They're looking at too small a sample size," he said .

Watts, who has been involved in clinical trials with bisphosphonates, said the drug studies typically have thousands of subjects and "we don't see these fractures."

The link could be a chance association, said Watts, who has been a consultant for makers of osteoporosis medications. "If there is a causal association," he said, "it appears to be limited to a small subset."

Neither Rosenwasser nor Lane is suggesting that bisphosphonates be abandoned. Both agree they can help soon after a diagnosis of osteoporosis. But after a certain point, they said women may be better off going off the drug or switching to another type of osteoporosis drug.

More information

To learn more about fractures, visit the American Academy of Orthopaedic Surgeons  .

WEDNESDAY, March 10 (HealthDay News) -- Two new studies report a high rate of severe injuries -- including amputations, spinal injuries and even death -- among children who ride all-terrain vehicles.

"A spine injury is such a devastating injury for a young person," said Dr. Jeffrey R. Sawyer, an assistant professor of orthopaedics with the Campbell Clinic at the University of Tennessee, and a co-author on both papers.

The same goes for amputations, which, as a result of these types of injuries, have typically been of legs, toes and fingers.

The findings were to be presented Wednesday at the American Academy of Orthopaedic Surgeons annual meeting, in New Orleans.

"ATV [all-terrain vehicle] injuries have been significant; we've been noticing increases for a while," said Dr. Mike Gittelman, an associate professor of clinical pediatrics in the division of emergency medicine at Cincinnati Children's Hospital.

Gittelman, who was not involved with either study, said ATV-associated fatalities increased nearly 60 percent between 2000 and 2005, while non-fatal injuries rose 48 percent.

Three-wheeled ATVs have been banned (although some do still exist), but four-wheeled, multi-rider ATVs are gaining in popularity and it appears they are not necessarily any safer, the researchers said.

The first set of authors reviewed emergency-room records at a trauma center in California for all patients who had sustained injuries in an off-road vehicle from Jan. 1, 2005 through the end of 2007. There were about 110 patients in total.

People involved in an accident with a multi-rider ATV were more than 10 times as likely to need an amputation as people involved in an accident with a conventional single-rider ATV, the study found.

"It's night and day. If you get injured on one of these it's going to be bad," said study author Dr. Gregg Wendell Schellack, an orthopedic surgery resident at Loma Linda University Medical Center, who races motocross and dirt bikes.

The second study found that almost 4,500 U.S. children were injured in an ATV-related accident in 2006, with 7.4 percent sustaining a spine injury. That represented at least a 140 percent increase in the overall number of children injured since 1997 and a 467 percent increase in spinal injuries.

Seventy percent of these injuries occurred in children under the age of 16. Spinal injuries were more common in older girls.

A third study found severe injuries among children who had participated in motocross, a sport involving off-road, two-wheeled motorcycles.

Half of the children who had sought treatment for this type of injury at a single trauma center were hospitalized and nearly one-third needed surgery. Many had been wearing helmets and other protective gear.

The dramatic increase in the number of ATV-related injuries could be due to any number of factors, including the number of vehicles on the road: In 1985, there were about 400,000 ATVs in the United States, said Sawyer, while today there are an estimated 9.2 million.

There's also the size and power of the vehicle to be considered. In the 1970s, the typical ATV weighed about 250 pounds and was 7 horsepower. The newer vehicles weigh much more than that and can approach speeds of 100 mph, Sawyer said.

They also have a higher center of gravity, making them more prone to roll over, Schellack explained. "If it starts to roll over, your first instinct is to put your foot down to try to stabilize or brace it, but that's no match for a 1,000-pound vehicle."

And children just shouldn't be riding these vehicles, added Gittelman. "They don't possess the maturity or ability to operate these vehicles," he said. "If you're not going to let a kid drive [a car], why would you let them drive a vehicle that's just as powerful?"

More information

The American Academy of Orthopaedic Surgeons   has more on ATV safety.

SATURDAY, March 6 (HealthDay News) -- Electromagnetic pulses from a portable device can significantly reduce pain and inflammation in people suffering from osteoarthritis of the knee, a new study suggests.

Researchers gave a battery-operated device to 34 people, who used it to emit a low-intensity, pulsating, electromagnetic frequency to their knees. The participants experienced pain relief of more than 40 percent on the first day of treatment, according to the study.

The approach has no side effects, is "relatively low-cost in the long-run and the onset of pain relief is immediate," Dr. Fred Nelson, associate program director for research and director of the Osteoarthritis Center at Henry Ford Hospital, said in a hospital news release. "We look at electromagnetic pulses as a potential way to improve quality of life and independence for those who suffer from osteoarthritis of the knee."

The electromagnetic pulses are thought to reduce the level of calcium in cartilage cells and set off a process that reduces inflammation.

"We are really fine-tuning what we are doing to the cell environment with a very specific pulse sequence and frequency," Nelson said.

For the study, people wore the device around their knees for 15 minutes, twice a day for six weeks.

Nelson was scheduled to present the findings at the annual meeting of the Orthopaedic Research Society, March 6 to 9 in New Orleans. The study was funded by Ivivi Health Sciences, which developed the device.

More information

The Arthritis Foundation has more on osteoarthritis  .