The FDA has approved the use of hyaluronates for intra-articular injections to treat osteoarthritis in the knee. Hyaluronates are also approved for intradermal use to correct moderate-to-severe facial wrinkles and folds and in ophthalmic surgeries.
Hyaluronates are considered treatments or therapies and are not classified as drugs. To take advantage of the exploding epidemic of arthritis, Pharmaceutical manufacturers have developed treatments that inject a form of hyaluronan into the knee joint. The form of the compound varies between hyaluronic acid, its salt sodium hyaluronate, or a hylan polymer. The source of the hyaluronan also varies and may be of avian, bovine or human derivation.
All of these treatment for arthritis consists of a series of from three to five injections directly into the articular cartilage of the knee. The procedure is known as viscosupplementation and takes place over several weeks. The injection of a local anesthetic, such as lidocaine, precedes the actual injections.

Viscosupplementation is the name given for the injection of a gel-like substance (hyaluronates) into the joint to improve the viscous properties of synovial fluid. Hyaluronate injections are often referred to as joint fluid therapy or joint fluid prosthesis.  
These intra-articular injections deliver hyaluronan or hyaluronate to the site of inflammation and cartilage degradation. The purpose of hyaluronates is to restore the cushioning and lubricating properties of the joint.
These treatments are now limited only to treat knee arthritis. Their manufacturers expect approval for other large joints (hips and shoulder) in the future. These injections are expensive (up to $500), which are covered by insurance in patients who have failed to respond to conservative therapy and simple analgesics. Pain relief is believed to last from five months to a year.  

Hayalgan  was the first viscosupplement approved by the FDA in 1997. Hyalgan is is a solution of sodium hyaluronate and is injected directly into the knee joint once a week, one week apart, for a total of five injections over nine weeks.  

Synvisc was approved by the FDA in August of 1997. Sinvisc is manufactured by Genzyme and is chemically known as Hylan GF 20. Synvisc injections are typically given once a week, 7 days apart, over a 15-day period, for a total of three injections.
In the first session the diseased osteoarthritic synovial fluid is typically removed from the knee before the first injection.

Supartz was the first hyaluronan therapy developed. It was introduced in Japan in 1987 but was not approved by the FDA until January of 2001. Supartz is manufactured by Smith and Nephew. It is a solution of sodium hyaluronate and is injected once a week for 5 weeks. Supartz is the most prescribed joint fluid therapy on the market with over one hundred million injections sold worldwide.

Orthovisc is the latest hyaluronan therapy approved by the FDA. It is manufactured by Anika Therapeutics and was approved in February 2004. Orthovisc is a solution of high molecular weight hyaluronan and is injected once a week for four weeks. Orthovisc is structurally similar to human synovial fluid, the substance that lubricates joints.