The use of intra-articular (IA) and IV hyaluronic acid for the treatment of chronic arthritis, also called osteoarthritis or degenerative joint disease, has become common. Hyaluronate sodium is the sodium salt of hyaluronic acid (HA) which is a naturally occurring high-viscosity mucopolysaccharide. In the joint this very long molecule is found both in synovial membrane, joint fluid, and as part of the cartilage matrix. If forms a backbone to which other mucopolysaccharides, keratin and chondroitin sulfate, are attached. The main physiological actions of HA are cushioning the joint, providing lubrication for the joint surfaces to glide over each other, scavenge inflammatory molecules before they damage the cell of the cartilage surface.

Besides Legend (Bayer) a number of products are now marketed:

• Hyalovet (Fort Dodge)
• Hyvisc (Boehringer Ingelheim)
• Hylartin (Pharmacia & Upjohn)
• and others including some generic products not specifically approved for use in the horse.

This article discusses the effect of hyaluronate in joints with arthritis, evidence for efficacy in the treatment of lameness do to DJD, adverse reactions, and dosage regimens.

Hyaluronate naturally increases in joints that are arthritic and may be a response by the cells to help limit damage. HA has been shown to have the following effects in such instances:

• moderate analgesic (pain relief) effects
• decrease the production of inflammatory chemicals
• may hinder the movement of inflammatory cells