Viscosupplements are injectable products that come in three varieties of injection regimens. The exact mechanism of their action is unclear, but the therapy works by increasing the viscoelasticity of the synovial fluid, thereby reducing friction between the joints. The immediate short-term benefit appears to be mainly pain relief, more so than actual healing, although this does allow for long-term improvements in mobility and range of motion. The products are appropriate in cases where the patient has failed to respond to pharmacological or steroid therapy and there is no contraindication to injection therapy. The effectiveness of these products has mainly been established for the knee joints, and has not yet been very well established for use in other joints of the body.
Viscoelasticity is a property describing the ability to absorb shock. Fluids that have a high degree of this property provide greater resistance to sudden shocks and impacts than they do to loads that are applied gradually. In an osteoarthritic knee, the cartilage wears faster than it can repair itself. The shock-absorbing quality of hyaluronic acid products reduces this wear on the articular cartilage, allowing it to heal. The product itself does not remain in the joint space long after injection, as it lasts only hours or days. The therapeutic benefit, however, can last up to half a year, indicating that there may be some element of anti-inflammatory action or stimulation of the body’s natural ability to replenish the joint fluid. Because there is no pharmacologic action associated with the treatment, these products are classified as medical devices in the majority of circumstances. In India, however, most HA products are classified as drugs.