In 2006, a team led by Nicholas Bellamy, MD, of the University of Queensland in Brisbane, Australia, reviewed 76 studies examining the use of hyaluronic acid for treating knee osteoarthritis. The review, the largest and most comprehensive of its kind, found that pain levels in the average patient who receives these injections are reduced by 28 to 54 percent. That’s roughly what a patient might expect from taking NSAIDs, the authors concluded. Meanwhile, hyaluronic acid improved the ability to move about and perform daily activities by 9 to 32 percent.

As a patient soon learns, though, hyaluronic acid is no quick fix. According to Bellamy’s review (which was conducted on behalf of the Cochrane Collaboration, an international consortium that reviews scientific evidence for medical treatments), it takes about five weeks, on average, before a patient experiences the full benefits of hyaluronic acid. By contrast, corticosteroid injections – the other primary treatment choice when NSAIDs aren’t an option – provide significant relief within a few days. However, pain relief from corticosteroids diminishes markedly within a month or so. What’s more, overuse of corticosteroids can have a catabolic effect – that is, it could cause cartilage to break down and deteriorate further, explains Case Western Reserve University rheumatologist Roland W. Moskowitz, MD. Meanwhile, the Cochrane review found that pain-relieving benefits of hyaluronic acid persist at peak levels for about three months, on average. Dr. Moskowitz sometimes gives patients a double shot in the knee – one injection each of hyaluronic acid and corticosteroids – for quick-acting, long-lasting relief.

Variable Response

Of course, large studies like the Cochrane review reflect how the average individual responds to a therapy; as the old saying goes, your results may vary. About 30 percent of people who undergo hyaluronic acid injections become virtually pain free, and symptom relief may last up to two years, says UCLA rheumatologist Roy D. Altman, MD. Yet, another 20 percent of patients experience no benefit. Unfortunately, adds Dr. Altman, “we don’t know how to pick out those people who are going to have an outstanding response versus a modest response versus no response at all.” He and his colleagues have tried to identify ways to predict how a patient will respond to hyaluronic acid, but so far have come up empty.