TUESDAY, Sept. 25 (HealthDay News) -- The number of Americans getting knee replacement operations has jumped more than 100 percent over the past two decades, keeping many more older adults active and independent, a new study finds.

At about $15,000 an operation, however, the costs to Medicare and other insurers have also ballooned. But experts analyzing fees associated with the procedures say that added productivity and mobility may offset the initial outlay.

Knee replacement is cost-effective, said Dr. Matthew Hepinstall, an orthopedic surgeon at Lenox Hill Hospital in New York City. "This is a surgery that can actually pay for itself in the increased productivity of the person who goes from disability to return to work," said Hepinstall, who was not involved in the study. There are also savings in disability payments and the costs of ongoing care, he said.

The study, published in the Sept. 26 issue of the Journal of the American Medical Association, found that roughly 600,000 knee replacements are done on Medicare enrollees -- patients 65 and older participating in the government's health insurance -- each year in the United States. The total cost of all these knees is $9 billion, the researchers say.

In the 20 years between 1991 and 2010, first-time knee replacements jumped 162 percent, the study found. Revisions (replacement of an artificial knee) increased about 106 percent in that time period.

Lead researcher Dr. Peter Cram, an associate professor of medicine at the University of Iowa Carver College of Medicine in Iowa City, credits the burgeoning baby boom generation and better success rates with the procedure's popularity.

"We are doing more procedures as the population ages," Cram said. In addition, a higher proportion of that aging population wants the surgery, he said.

With many years of practice, the operation is very safe and the rate of complications remains low, Cram added. For people with severe knee damage, a knee replacement can relieve pain and restore movement.

To examine the effects of knee replacements on health costs, Cram's team collected data on almost 3.6 million Medicare patients who had a knee replacement or a revision of an initial knee replacement in the previous 20 years.

The investigators found initial knee replacements rose 76 percent and revisions increased 99 percent. While success rates were consistent over the period, the number of hospital readmissions within 30 days inched up from 4.2 percent to 5 percent in initial knee replacement patients and from about 6 percent to almost 9 percent among revision patients. That rise in readmissions is largely related to shorter initial hospital stays today, Cram said. After an initial knee replacement, patients now leave the hospital in 3.5 days versus 7.9 days in the mid-1990s, the study found.

Wound infections were one reason for readmissions, but the authors weren't certain of the cause.

Cram said knee replacements last 15 to 20 years, which means many patients may live long enough to need a second operation. However, the newer implants may last longer than the earlier models, he said.

"Implants we are implanting today are different than the one we used 10 to 15 years ago," Cram said. "Hopefully, they're newer and better, but we don't really know that."

Recovery from a knee replacement takes about three months and requires patients to undergo physical therapy. Results depend on the surgery itself and the patient's willingness to work on moving the knee, said Hepinstall.

The study also found that more obese and diabetic patients get new knees nowadays, and more patients are getting outpatient rehabilitation than two decades ago.

The authors cautioned that the study findings might not apply to younger populations or other elderly groups, noting they looked only at fee-for-service Medicare enrollees -- who make up 60 percent of new-knee recipients -- and not managed care Medicare enrollees.

More information

For more information on knee replacement, visit the American Academy of Orthopaedic Surgeons  .

FRIDAY, April 6 (HealthDay News) -- Overuse injuries account for more than one-quarter of all injuries suffered by U.S. collegiate athletes, a new study has found.

Women -- especially those who played field hockey, soccer, softball and volleyball -- accounted for the majority of the overuse injuries (62 percent).

For this study, researchers analyzed three years of data from male and female collegiate athletes participating in 16 team sports at the University of Iowa.

During the study period, 319 male athletes sustained 705 injuries and 254 female athletes suffered 612 injuries. Overall, 288 athletes reported more than one injury. Of all the injuries suffered by the athletes, 29 percent were overuse injuries and 71 percent were acute injuries.

Overuse injuries tend to occur gradually and are caused by repeated small injuries, without a single, identifiable event. Acute injuries -- typically suffered by athletes playing high-speed and full-contact sports such as football or hockey -- have specific and identifiable causes.

The most common overuse injuries were general stress (27 percent), inflammation (21 percent) and tendinitis (16 percent).

Overuse injuries were most common among athletes in low-contact sports that involve long training sessions or in which athletes repeat the same movement numerous times, such as long-distance running, rowing and swimming. Four women's sports in particular -- field hockey, soccer, softball and volleyball -- had the highest rates of overuse injuries.

The study appears in the April issue of the Journal of Athletic Training.

"Overuse injuries may present not only physical challenges, but also psychological ones that could significantly affect an athlete's recovery and performance," study co-author Tracey Covassin said in a journal news release.

"Understanding the frequency, rate and severity of overuse injuries is an important first step for designing effective injury-prevention programs, intervention strategies and treatment protocols to prevent and rehabilitate athletes with these types of injuries," Covassin said.

More information

The American Academy of Orthopaedic Surgeons has more about common sports injuries and conditions  .

(HealthDay News) -- Rheumatoid arthritis is triggered by an overactive immune system that attacks the body's own joints, causing flares of pain and stiffness.

The American College of Rheumatology says about 13 million Americans have the disease. The ACR recommends regular exercise, except during painful flares.

Here's more of its expert advice:

• When joints are painful or you feel tired, stick to gentle range-of-motion exercises to help keep the joints flexible.
• When you are feeling well, focus on muscle-strengthening and low-impact cardiovascular exercises.
• Work with a physical or occupational therapist to determine which exercises and intensity are best for you.
• Feelings of anxiety, depression or isolation are common. Your health care provider can help you work through these feelings, which tend to subside when you're feeling better.