Hower, hyaluronic acid isn't universally approved. In June 2013, the  American Academy of Orthopedic Surgeons (AAOS) issued a new set of recommendations for the treatment of knee OA. Based on a review of 14 studies, the organization determined hyaluronic acid did not meet the minimum clinically important improvement measures, according to David S. Jevsevar, MD, chair of the evidence-based practice committee for the AAOS.

With five brands available in the United States, it’s natural to ask which is most effective. There have been relatively few head-to-head comparisons of the various products in clinical trials. “My sense is that they all work about the same,” says Dr. Jevsevar, a view shared by many other physicians who use the treatments. Likewise, the risk of side effects is similar among the different products, the most common being pain and swelling at the injection site that fades within a few days.

Beyond the question of how well viscosupplements work lies another intriguing area of inquiry: How do they work? Hyaluronic acid may act as a lubricant and shock absorber, but “there’s more to it than that,” says Dr. Moskowitz. “Hyaluronic acid has a lot of other activities in the joint.” For example, research suggests that hyaluronic acid interfere with prostaglandins and cytokines, naturally occurring compounds that promote inflammation.

What’s more, studies indicate that injecting supplemental hyaluronic acid may coax the joint into increasing its own production of this important substance, which may in turn help to preserve cartilage. “There’s a lot of data to suggest that it can slow the disease down,” says Dr. Moskowitz, a coauthor of the Osteoarthritis Research Society International recommendations on treating hip and knee osteoarthritis. “Hyaluronic acid is not a magic pill,” says Dr. Moskowitz. “But it has a definite role in the armamentarium for treating osteoarthritis of the knee.”