What is viscosupplementation?
Viscosupplementation is a therapy for moderate (not end stage) OA for which standard medical management fails. The therapy consists of injecting hyaluronan into the affected joint. It is FDA-approved only for the knee but has been used in the temporomandibular joint, shoulder, hip, and ankle. Hyaluronan (sodium hyaluronate) is a glycosaminoglycan found in the synovial fluid that allows viscous lubrication at low loads and shock absorbency at high loads. In the synovial fluid of a normal joint, there is 4 to 8 mg of hyaluronan with a molecular weight of 5 million daltons. In the synovial fluid of an osteoarthritic joint, there is less hyaluronan with a molecular weight of 2 to 3 million daltons, making it less effective for lubrication/shock absorbency.
Intraarticular hyaluronan appears to be safe and can be repeated in patients who get prolonged improvement (>18–26 weeks). Reported side effects include local injection reactions, systemic allergic reactions (especially in patients allergic to avian proteins, feathers or eggs; of note, the Euflexxa formulation is not made with bird or egg products), and “pseudoseptic” reactions (more common with Synvisc) often times resulting from CPP arthritis. Hyaluronan may have chondroprotective (stimulates proteoglycan synthesis), antiinflammatory (scavenger sink for inflammatory mediators), and antinociceptive effects, which may explain its prolonged symptomatic benefit, even though the hyaluronan can only be detected for a few days (intraarticular half-life is 17–36 hours) in the joint after the injection. There are several different formulations with varying molecular weights, composition, side-effect profiles, and frequency of injections. None are superior to another. If a knee effusion is present, the synovial fluid should be drained before injection of hyaluronan in order to get best results.
