An alternative medicine approach to joint pain that typically uses injections of sugar or sodium may be worth trying for knee osteoarthritis after traditional approaches fail, a recent review suggests.

Knee osteoarthritis, a leading cause of pain and disability in older adults, occurs when flexible tissue at the ends of bones wears down. While it can't be cured, physical therapy or anti-inflammatory medications are often prescribed to relieve pain and improve mobility.

Researchers examined data from 10 previous studies of what's known as prolotherapy, which is often used for chronic back pain. Prolotherapy involves injecting a solution of natural irritants like sugar or sodium next to the site where soft tissue like ligaments, tendons or muscle were injured or tore away from the bone.

Results from these studies, which had a total of 529 patients, suggest that prolotherapy may be a safe way to help ease pain from knee osteoarthritis. But the evidence on the effectiveness of prolotherapy isn't strong enough to recommend it until after other treatments fail, said senior study author Dr. Nicola Maffulli of the University of Salerno in Italy.

"There is no evidence that prolotherapy should be tried as a first line therapy," Maffulli said by email. "It should always be part of a holistic management plan, with weight reduction, activity changes, and physiotherapy."

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Ideal patients for prolotherapy might include people with mild to moderate knee osteoarthritis who don't get relief from medication or physical therapy, Maffulli added.

Across all of the studies that Maffulli and colleagues reviewed, most tested injections containing dextrose (a sugar), and two combined dextrose and sodium. A few tested dextrose solutions that also contained anesthetics like lidocaine or ropivacaine.

Participants reported improvements in pain, function and range of motion with prolotherapy and also reported high levels of satisfaction with the treatment.

But these small studies had such different designs and patient populations that it wasn't possible to do a pooled analysis of all data from all the studies to determine if there was a meaningful benefit in a larger group of people, researchers report in the British Medical Bulletin.

Eight of the 10 studies were of poor quality, researchers concluded. Most studies didn't report what's known as an effect size, or how much more pain relief people got from prolotherapy than from no treatment or from other interventions.

None of the studies reported dangerous side effects from prolotherapy, and the researchers note that the solutions injected may not cost much or be difficult to administer.

The trouble with knee osteoarthritis is that evidence is mixed for other options, too, said Dr. Regina Sit, a researcher at the Chinese University of Hong Kong who wasn't involved in the study.

"Conservative therapies such exercises, physical therapy, oral analgesic medications and complementary therapies such as acupuncture and herbal treatment have marginal effectiveness," Sit said by email.

Joint injections are a common approach for this type of pain, Sit added. Clinicians might inject corticosteroids or hyaluronic acid, which is similar to a lubricant found naturally in joints.

While it's possible prolotherapy may be safe and effective, research to date doesn't offer a clear picture of how this option stacks up against other types of injections for knee osteoarthritis, Sit said.

"Studies are needed to conclude which injection therapy should be given higher priority in routine clinical care," Sit added.