By Amanda Hedges, DVM, cVA, CVSMT
What is Osteoarthritis?
A healthy joint relies on the production of synovial (joint) fluid to lubricate structures, bring in nutrients and clear away cellular waste products, and to transmit forces through the leg. Healthy synovial fluid is produced by cells in the cartilage in response to movement. Some components of healthy joint fluid include hyaluronic acid (HA) and polyglycosaminoglycans (PGAGs). Inflammation due to an acute traumatic event, chronic low-grade trauma/wear and tear, or a joint infection impedes the production of healthy joint fluid. Specifically, pro-inflammatory molecules damage cartilage. In general, inflammation leads to pain, as the joint loses its ability to lubricate, bring in nutrients and remove waste, and transmit force. In response to this pain and instability, the body attempts to stabilize the joint, remodeling it to limit mobility. The joint capsule becomes thickened and bone proliferates around the joint in an attempt to immobilize the damaged area.
What are the Signs of Osteoarthritis and How Do We Diagnose It?
In its advanced stages, signs of arthritis are hard to miss. These include clear lameness and/or visible joint distortion by extensive bone proliferation. However, signs can start subtly and the horse may be able to compensate, depending on the level of performance.
These milder signs may include uneven wear on the hoof/shoe, difficulty holding up a limb for the farrier, decreased performance abilities, difficulty standing square, difficulty laying down or getting up, or behavioral changes.
When dealing with an infected joint, joint fluid is sampled and analyzed for markers of inflammation. If arthritis is secondary to “wear and tear,” diagnostic imaging (radiographs, ultrasound, CT) is the best way to confirm the diagnosis. Diagnostic nerve blocks may be used during workup to both hone in on a particular joint and to shed light on the clinical significance of the changes seen on imaging.
There are three objectives of treatment: 1) decrease inflammation, 2) prevent further damage, 3) relieve pain. It is immensely important to remember that there is no one-size-fits-all program for treating arthritis. If there was, everyone would do it and we wouldn’t have so many options! It is always critical to work with your veterinarian to determine the best plan based on your goals for your horse; making sure to discuss reasonable expectations for treatment and possible costs.
Oral supplements rely on research in horses and other species to make claims for effectiveness. Challenges of oral supplements include lack of FDA-regulated supply, mixed results from evidence-based-research, widespread anecdotal claims, and palatability. Oral supplements can be beneficial in that they can be less expensive than some treatments and are relatively easy to administer. It is important to weigh out the cost vs. possible benefit as compared to injectable joint therapies long-term. Learn more about assessing oral joint health supplements...
Diclofenac (Surpass®) is an anti-inflammatory drug formulated to penetrate the skin and provide local anti-inflammatory actions and pain relief. This drug is in the same class as oral non-steroidal anti-inflammatory drugs, so care should be used to minimize negative systemic side effects when both topical and oral products are used together. Occasionally a skin reaction can be seen, and owners should wear gloves when applying this product. Many other topical options are available on the market or through your veterinarian. As with any product, discuss the benefits and possible risks with your veterinarian.
The staple of anti-inflammatory drugs in horses is a class of drugs called non-steroidal antiinflammatory drugs (NSAIDs). Most commonly used are phenylbutazone (Bute®), flunixin meglamine (Banamine®), firocoxib (Equioxx®), and naproxen. These drugs act by halting the systemic inflammatory cascade at different points. Unfortunately, non-specific blocking of the cascade can also decrease other necessary pathways, resulting in the risk of damage to the stomach in the form of gastric ulcers, risk of damage to the intestinal lining resulting in colitis, and risk of kidney disease. Equioxx® is the most pathway-specific option and is often preferable for prolonged use (up to two weeks) but still carries some degree of risk.
Oral steroids can also decrease systemic inflammation. Unwanted side effects of prolonged steroid use in horses include immune suppression and laminitis.
Legend® and Adequan® are injectable joint support supplements both labeled for the prevention and treatment of arthritis. They may provide systemic anti-inflammatory effects. No contraindications are listed for either drug, but the risk of a site reaction applies, as with any intramuscular injection or intravenous injection.
Legend® is a synthetic hyaluronic acid (HA) that has been studied to treat carpal and fetlock arthritis secondary to non-infectious causes. It can also be used in the joint for local anti-inflammatory therapy. It can be used as a weekly intravenous injection for 3 weeks, monthly, or at your veterinarian’s discretion.
Adequan® is a synthetic polyglycosaminoglycan (PGAG) that has been studied to treat carpal and hock arthritis secondary to non-infectious causes. It is injected into the muscle every 4 days for a total of 7 injections, or at your veterinarian’s discretion.
Note that both of these products were studied in young adult healthy horses, and their effect on a horse outside of this age-range is only anecdotal. However, both are widely used in veterinary medicine.
Similar to oral steroids, long-acting injectable steroids may improve your horse’s comfort. Most common is a long-acting steroid that can provide systemic anti-inflammatory relief. Notable risks include site-reaction, immune-suppression, and risk of laminitis.
The body’s goal with producing excess bone around the joint is to decrease motion in the joint. In some cases, such as pastern or hock arthritis, we can help the body achieve this goal by fusing the joint (aka arthrodesis). Fusion can be hastened by injecting the joint with chemical irritants. Surgical procedures can also hasten joint fusion. Screws, plates, and/or cartilage drilling can all be employed to immobilize the joint. While these options may involve a greater initial cost, the chance of long-term comfort may make joint fusion a good choice for your horse.
Anti-inflammatory drugs, synthetic joint components, and biologically derived anti-inflammatory products can all be injected directly into an arthritic joint to improve comfort. Steroids such as betamethasone and triamcinolone, often in conjunction with synthetic joint fluid components such as hyaluronic acid, can be injected under standing sedation and can provide targeted relief. Methylprednisolone acetate may decrease inflammation and impair cartilage health, making it a good potential choice for joints that are easy to fuse (such as the hock joints or pastern joints). Polyacrylamide gel (PAAG) is a synthetic gel that can be injected into a joint to add physical stability to a joint, although more research is needed before equine use can be recommended.
Regenerative medicines such as interleukin-1 receptor antagonist protein (IRAP), Prostride®, stem cells, and platelet-rich plasma (PRP) may decrease inflammation and improve comfort in an arthritic joint as well. Anti-inflammatory mediators are removed and processed from the horse’s own blood, bone marrow, or fat tissue (depending on which therapy), and injected into the joint. This option may be preferable in a patient for whom steroids are not a good choice or depending on the nature of the injury. Learn more about these regenerative medicine modalities...
Risk of joint infection or joint flare is present anytime a joint is injected. These risks are decreased by the use of sedation to prevent mobility and sterile injection technique. Dose and frequency of treatment depends on response to treatment.
Acupuncture, chiropractic medicine, massage, light/laser therapy (usually Class 2 or 3), pulsed electromagnetic field (PEMF) therapy, thermal therapy, vibration floor plates, and controlled exercise programs may also improve comfort. Acupuncture creates a systemic release of endorphins and improves blood flow to painful areas. Chiropractic medicine relies on a high-velocity, low-amplitude thrust to a restricted joint (usually in the spine) to theoretically improve blood flow and nerve function. Massage can improve circulation and interrupt pain receptors. Light/laser therapy transmits energy in the form of light to cells, stimulating healing and pain relief. PEMF therapy (Assisi Loop®) pulses energy to cells via an electromagnetic current to stimulate healing and pain relief. The vibration floor plate VitaFloor® has been shown to improve topline muscle mass and improve circulation throughout the body. Learn more about equine acupuncture and chiropractic medicine...
Perhaps the tool that has the greatest potential benefit and least cost is controlled exercise. A regular low-impact exercise program, such as walking for 20 minutes daily, can improve joint health and mitigate the potential injury and inflammation that comes from weak postural muscles and stiff joints. Exercises that focus on postural strength and core stability, low-impact mobilization of joints, and mental stimulation can benefit the arthritic patient. Equine rehabilitation facilities offer exercise programs, hydro-treadmills, and swimming pools to achieve equine fitness goals. Talk to your vet for more details!
Other resources to consider:
“Equine Joint Therapies: What to Know” by Erica Larson, published by The Horse
“Lameness & Joint Medications” by Benjamin Espy, DVM, DACT and Justin Harper, DVM, MS, DACVS, LA, published by the American Association of Equine Practitioners (AAEP)
“Equine Osteoarthritis: Early Interventions” by Natalie DeFee Mendik, MA, published by The Horse
“What You Need to Know about Equine Osteoarthritis” by Stacey Oke, DVM, MSc, published by The Horse
“Alternatives for Managing Osteoarthritis in Horses: PAAG and Stanolozol” by Alexandra Beckstett, published by The Horse