Do Injections Help Arthritic Knees? Jury Still Out
Wed Feb 13, 2:01 PM ET
By Faith Reidenbach

NEW YORK (Reuters Health) - In people with osteoarthritis, injections of a drug called hyaluronate sodium into the knee are as good as anti-inflammatory drugs at relieving pain at rest, Canadian researchers report.


For activity-related pain, the injections may be even better, they say. But in the journal where the report is published, other experts dispute the conclusions, saying they are not supported by the study results.

Osteoarthritis is a disease caused by the general "wear and tear" of aging. The cartilage in joints breaks down, leading to pain and stiffness. Part of the problem is that the concentration of a substance called hyaluronic acid declines in the fluid inside joints.

Hyaluronic acid "acts as a 'lubricant' when movements are slow," Dr. Robert Petrella and colleagues explain in the Archives of Internal Medicine (news - web sites) for February 11. It acts "as a 'shock absorber' when movements are fast."

The theory behind injecting hyaluronate sodium into a joint, which is a relatively new osteoarthritis therapy, is that the injections will restore joint levels of hyaluronic acid, resulting in pain relief and improved function. Some of the earliest research into joint injections for osteoarthritis was actually done in racehorses. A number of studies of hyaluronate injections in humans have been conducted, but none have examined their effect on activity-related pain.

To investigate, the research team randomly divided 120 patients with an average age of 67 into four groups. All patients received pills and three weekly knee injections, but some were given placebo (inactive) pills or anti-inflammatory drug-containing pills and some received placebo injections (salt water) or hyaluronate injections. In addition, patients in all groups were asked to do 10 minutes of resistance exercises at home, at least 3 days a week.

Compared with the beginning of the study, pain at rest improved in all four groups by week 4, even those getting placebo pills and placebo injections, Petrella's team found. This suggests that the exercise alone may be helpful, they conclude.

Also, all patients getting one or both active treatments reported significant improvement in overall pain, activity-related pain and disability after four weeks compared with the beginning of the study.

But only the two groups getting hyaluronate injections seemed to improve between week 4 and the end of the study at week 12. The researchers conclude that hyaluronate injections are as effective as anti-inflammatory drugs at treating arthritis pain at rest, and may even be superior to exercise alone or anti-inflammatory drugs alone for relieving pain with physical activity and boosting daily function, such as walking and stair climbing.

The other experts, Dr. David Felson of Boston University and Dr. Jennifer Anderson, point out in an editorial that while Petrella and his associates showed improvement within groups, they did not provide statistical data supporting their conclusion that hyaluronate sodium might be more effective than placebo.

"There is considerable evidence" that the reverse is true, "that hyaluronic acid is no more effective than salt water injections for the treatment of knee osteoarthritis," Felson told Reuters Health. When he and Anderson reviewed published reports from three large, well-designed published trials of hyaluronate sodium injections for knee osteoarthritis, they found no benefit of the injections over placebo.

Furthermore, when Felson and Anderson reanalyzed the new data by a method they consider more appropriate, they determined that neither hyaluronate injections nor anti-inflammatory drugs were any better than a placebo in the Canadian study. Despite the researchers' conclusion, "we find no evidence to suggest that hyaluronate sodium in this trial is more effective than placebo," they write.

However, more study may still show an effect, Petrella said.

"We were looking at a within-group difference," Petrella told Reuters Health, responding to the editorial. "To provide a between-group analysis, we would have required large numbers of patients, beyond the scope of this particular trial....We didn't have the funding to perform that type of trial.

"We need to do further long-term studies to see if that trend continues," Petrella added, referring to the trend for additional improvement in the hyaluronate injection groups after week 4. "What we think from the data, although we didn't have statistically significant results, was that there may be some differentiation between the two modalities of therapy, the NSAIDs (anti-inflammatory drugs) and the hyaluronic acid: some being related to immediate pain control and analgesia, as opposed to the other (being related to) function-related pain improvement."SOURCE: Archives of Internal Medicine