Each of a horse’s joints is comprised of two ends covered by articular cartilage and encased within a joint capsule. The capsule’s inner layer is called the synovial lining; this secretes synovial fluid, which prevents friction between the joint structures.1 The outside layer of the capsule is fibrous, which helps to stabilize the joint. The articular cartilage contains collagen, proteoglycans, and water. Proteoglycans are molecules that help maintain the elasticity of connective tissue and are made up of chains of glycosaminoglycans, a type of carbohydrate that give cartilage its stiff structure. Synovial fluid contains two things that give it lubricating qualities: hyaluronic acid (a glycosaminoglycan that is also present in cartilage), and a protein called lubricin.

A number of factors, such as overall health, activity level, medications and diet have an impact on joint health and the levels of synovial fluid in horses’ joints. 

Arthritis in the Horse: Acute and Chronic

Arthritis can develop in horses as the result of interference with normal structure and function. Damage to the cartilage and/or the bone through injury or infection results in roughening of the smooth surfaces. Movement of the roughened bone ends and/or damaged cartilage results in inflammation, that produces mediator chemicals that damage the synovial fluid, all of which causes swelling of the joint, pain and restriction of movement.2 This response is known as acute arthritis. Injury to the joint capsule and its ligaments can also trigger inflammation resulting in thickening of the capsule, reducing its elasticity and thinning of the joint fluid, thus reducing its ability to lubricate.

If untreated, new bone will be formed in response to surface damage. This new bone is rough and is not covered with protective cartilage.1 The new growth interferes with joint movement and causes pain. These long-term effects are called chronic arthritis.

Joint inflammation increases the amount of fluid in the joint, which can cause visible bulging of the joint capsule. Not all joint swellings are due to arthritis. Minor joint injury can cause joint swelling, but in cases of arthritis, there will be pain when the affected joint is flexed. The horse may also evidence lameness or stiffness. In acute arthritis, the swollen joint may appear warm to the touch.1,2

Degenerative joint disease (DJD) can result in the same changes in the long term, but it is usually not associated with pain or inflammation in its early stages. In DJD, joint structures respond to trauma by gradually changing shape and elasticity. Many horses with DJD continue to move soundly, while the progression in others leads to lameness.2

Sodium Hyaluronate for Joint Health in the Horse 

Sodium hyaluronate (hyaluronate sodium) is a mucopolysaccharide that is useful in the treatment of synovitis not associated with severe degenerative joint disease. It may be helpful to treat secondary synovitis in conditions where full thickness cartilage loss exists.3 Sodium hyaluronate is found normally in the connective tissues and synovial fluids of equines and many other animals. Because this compound is normally found in the horse's body, it does not create immune reaction when horses are treated with it.

Sodium hyaluronate can help in maintaining the joint health of horses. It also acts to inhibit inflammatory responses and improves the lubrication of the joint fluid. It is used both intravenously (injection directly into a vein) and intraarticularly (injection directly into a joint space).2,3 Most sodium hyaluronate products are approved for use in the fetlock and carpal (knee) joints, though they are also used in other joints (extra-label). Clinical trials have shown 90% or higher positive responses in horses treated with sodium hyaluronate, either intravenously or intra-articularly, for joint arthritis.

Some patients may develop local reactions manifested by heat, swelling, and/or effusion. Effects generally subside within 24-48 hours; some animals may require up to 96 hours for resolution. No treatment for this effect is recommended. Sodium hyaluronate is not recommended for horses with an infectious cause of joint inflammation, nor should it be injected into a joint with an associated fracture.2

Where to buy Sodium Hyaluronate

Sodium hyaluronate is available in the U.S. through pharmaceutical manufacturers and through veterinary custom compounding companies. SODIUM HYALURONATE 12.5 MG/ML by NexGen Pharmaceuticals is indicated for the treatment of synovitis and for the maintenance of joint health in the horse.

Please consult your veterinarian prior to beginning any treatment regimen.

FOR RX ONLY: A valid prescription from a licensed veterinarian is required for dispensing this medication.

1thehorse.com.

2vcahospitals.com.

3Plumb’s Veterinary Drugs.