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Viscosupplementation is based on the recognition that the elastoviscosity of synovial fluid in osteoarthritic joints is considerably lower than in normal joints which is resulted from reductions in the molecular size and concentration of hyaluronan (HA) in the synovial fluid. Viscosupplementation is therefore performed by intra-articular injection of HA or its derivatives in order to restore the elastoviscosity of the synovial fluid to normal or higher level. Since the limitation in viscosupplementation with HA preparation, hylans (chemically cross-linked HA) were developed. Hylan G-F 20 (Synvisc®), the particular hylans made up of hylan A in solution and hylan B gel slurry (80:20 v/v), are considered to be the rather ideal elastoviscous material used in viscosupplementation due to tissue and blood compatibility, permeability to metabolites and macromolecules, proper elastoviscous properties, and prolonged residence time. The mechanisms whereby hylan G-F 20 and HA preparations exert their therapeutic effects in osteoarthritis are believed to be mediated via several pathways such as restoration of elastoviscous properties of the synovial fluid, anti-inflammatory effect and anti-nociceptive effects, normalization of HA synthesis, and chondroprotection. In clinical trials, three weekly intra-articular injections of hylan G-F 20 are more effective than intra-articular injections of saline or lower molecular weight HA in treatment of osteoarthritic knees. In addition, hylan G-F 20 is at least as effective as NSAIDs in treating this condition, whereas the best results are found when both hylan G-F 20 and NSAIDs are combined. There are no reports on systemic reactions attributable to hylan G-F 20 treatment, while an incidence of local reactions (transient pain and swelling) is 2.1 % per injection. Hylan G-F 20 is therefore indicated for the relief of pain in patients who have failed to respond adequately to conservative treatments and may be considered as an alternative to NSAIDs, particularly in patients at risk for complications related to NSAIDs therapy.
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