Argentina's Juan Martin Del Potro recieves attention to his knee after falling at the 2013 Wimbledon Championships tennis tournament
The pill most often prescribed for knee pain - acetaminophen - may not help at all, researchers reported Monday.
The new study of what works for arthritis pain in the knee came up with some surprising results. The most common treatments often may not help much, and even a placebo injection of salt water provides more pain relief than any pill.
The findings go against what many doctors have long believed, although they didn't surprise veteran knee surgeons, who know pain relief varies greatly from one patient to another.
"All treatments except acetaminophen showed clinically significant improvement from baseline pain."
Dr. Raveendhara Bannuru and colleagues at Tufts Medical Center near Boston looked at thousands of studies on various treatments for knee pain, from acetaminophen - the active ingredient in Tylenol - to ibuprofen to steroid injections.
Finding the scientific truths is tricky. There's not much incentive for drug companies to test generic, over-the-counter drugs such as naproxen, and there's also not much reason to test an injection of a steroid against a generic treatment such as hyaluronic acid, a kind of joint lubricant.
But the team came up with 137 studies covering 33,000 people that met some high standards - they'd been blinded, meaning the doctors didn't know which treatment a patient actually got as they evaluated pain, stiffness and range of motion.
And most compared treatment to placebo - a dummy pill or dummy injection.
The results surprised them. "All treatments except acetaminophen showed clinically significant improvement from baseline pain," they wrote in their report, published in the Annals of Internal Medicine.
"Contrary to popular belief, our results showed that celecoxib (a prescription drug sold under the brand name Celebrex) was not superior to acetaminophen."
And a dummy injection of salt water worked better than any pill, although not better than injecting a steroid or lubricant.
It might be due to a super placebo effect, or it could be that injecting any fluid into the knee, called viscosupplementation, provides at least temporary relief, Bannuru and colleagues said.
Either way, it's a big issue for many people, and one that involves a whole lot of money, said Dr. Lisa Mandl of Weill Cornell Medical School in New York and Elena Losina of Brigham and Women's Hospital in Boston.
"The global viscosupplementation market is estimated to be $2.5 billion by 2017, and the market for glucosamine is estimated to be $12 billion by 2020," they wrote in an editorial.
"Almost 40 percent of the U.S. population older than 45 years has some degree of knee osteoarthritis and the estimated lifetime risk for knee (arthritis) is 14 percent," they added.
The Tufts team did not look at alternative treatments such as glucosamine and chondroitin sulfate supplements. Both the American Board of Internal Medicine and the American Academy of Orthopedic Surgeons say they don't work.
"Regardless, patients continue to demand these therapies," Mandl and Losina noted.
"When we inject something into the knee, patients are going to improve for at least four weeks."
This study may explain why. It is clearly difficult to tell which treatments work best for knee pain and relief may be highly subjective.
Dr. David Jevsevar, an orthopedic surgeon at Dartmouth Medical School and a chair of the Evidence-Based Quality and Value Committee of the American Academy of Orthopaedic Surgeons (AAOS), says it's hard to judge knee arthritis pain because it comes and goes.
"Patients with knee osteoarthritis typically don't have pain every day," Jevsevar, who was not involved in the research, told NBC News.
"They have good days and bad days. If you do nothing, 60 percent of patients are going to get better because of the ebb and flow of osteoarthritis. When we inject something into the knee, patients are going to improve for at least four weeks."
One finding that Jevsevar disagrees with was the Tufts team's assertion that hyaluronic acid provides pain relief. The AAOS specifically recommends against it.
"It's expensive," Jevsevar said. "It can cost $700 to $1,000 an injection. That is a lot of money for something that doesn't give you long-term benefit." Jevsevar believes the Tufts analysis was flawed because it set too low a bar for measuring pain relief.
Instead, Jevsevar says his organization recommends taking things slowly and going with the cheapest and least invasive treatment first. That may mean weight loss - it really does work - and ice. Exercise can help, too, if it's the right kind that doesn't strain the knee. Swimming and cycling fit that bill. Physical therapy may also help.
Next come over-the-counter treatments, including acetaminophen for many people, because it is non-toxic in recommended doses and doesn't cause stomach bleeding like other drugs, such as aspirin and ibuprofen, can. Steroid injections come next, but not unless pain pills don't do the trick.
"We believe that pharmacologic intervention is important for patients that can tolerate it," Jevsevar said. "We believe that surgery is a last resort."
At least one study has found that surgery is no better than medication and physical therapy for relieving the pain and stiffness of moderate or severe arthritis.
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