Intra-articular injections of hyaluronic acid relieved pain and produced functional improvements lasting at least 6 months in a pilot study of 75 patients with ankle osteoarthritis, reported Dr. Shu-Fen Sun of Veterans General Hospital, Kaohsiung, Taiwan, and associates.
Researchers have reported success with hyaluronic acid injections in osteoarthritic knees, so Dr. Sun and colleagues assessed the efficacy and safety of these injections in an open-label prospective clinical trial involving 41 men and 34 women with mild to moderate unilateral ankle osteoarthritis (OA). “To date there is only limited published literature on its use in the ankle,” and it is approved for clinical use only in the knee, they noted.
OA reduces the concentration of hyaluronic acid in the synovial fluid of affected joints. Intra-articular injections are thought to restore viscosity and elasticity in that fluid, as well as to normalize endogenous synthesis of hyaluronic acid and inhibit its degradation, the investigators said (Osteoarthritis Cartilage 2006;14:867-74).
Study subjects received five weekly intra-articular injections. Beneficial effects were noted within 1 week of completing the series of injections and persisted through a 6-month follow-up. On the Ankle Osteoarthritis Scale, a patient-rated measure that addresses pain and function in the affected joint, scores decreased significantly beginning at 1 week after treatment and continuing through 1-month, 3-month, and 6-month follow-up visits.
Similarly, on the physician-rated 100-point measure of the American Orthopaedic Foot and Ankle Society, which assesses pain, function, and alignment, mean scores improved from 64 at baseline to 75 at 1 week and 78 at all subsequent follow-ups.
The treatment decreased the patients' use of rescue analgesics. Acetaminophen use dropped from an average of 14 tablets per week at baseline to 3 tablets per week at 1-month, 3-month, and 6-month follow-up visits.
Ankle sagittal range of motion did not change significantly with treatment.
Given that surgical treatment of ankle OA “is often quite painful,” intra-articular hyaluronic acid injections may offer a new option to patients who have not responded to traditional pain therapies, Dr. Sun and associates said.
These findings support the idea that the treatment's mechanism of action exceeds simple replacement of viscous joint fluid. “Temporary restoration of the rheologic homeostasis may trigger normal native hyaluronic acid metabolism. Hyaluronic acid also fulfills an anti-inflammatory role by reducing white cell aggregation and activation. With this postulated disease-modifying behavior, its clinical effects may persist beyond its physical duration within the joint,” the researchers noted.