March 6 (HealthDay News) -- A single injection of hyaluronic acid is no more effective than a placebo in treating hip osteoarthritis (OA), a new French study finds.

Hyaluronic acid (HA), a substance found in normal joint fluid, is used to restore the elasticity of synovial fluid, which lubricates and protects joints. The use of HA injections to treat knee OA is approved by the U.S. Food and Drug Administration, but there's little evidence to support its use in treating hip OA.

This study included 85 patients with hip OA who were randomly selected to receive either a single injection of HA or a placebo. When the patients were assessed for pain, stiffness and disability three months later, the researchers found no difference between HA and placebo.

The study was published in the March issue of Arthritis & Rheumatism.

"The absence of any difference between treatment arms likely reflects the lack of clinical effect of one single intra-articular injection of HA for hip OA," wrote the researchers at the Henri-Mondor Hospital in Paris. The findings are similar to a recent review of other trials of HA injection in patients with hip OA.

A single injection of HA may not have much effect on knee OA, because it may be rapidly cleared from the synovial fluid compartment, the French team said.

"Future studies are warranted to confirm our results and to evaluate the effects of repeated HA injections in hip OA," they concluded.

SOURCE: Wiley-Blackwell, news release, March 3, 2009