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Equine Joint Disease:

Diagnosis and treatment of joint disease in horses.

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Joint Disease: Diagnosis and Treatment

Diagnosis of Joint Disease

Clinical signs of joint disease include lameness, swelling, excessive synovial fluid, pain on flexion, and heat. However, these signs alone don't tell you what joint structures are affected or how badly they are damaged.

A detailed examination is needed to determine a horse's exact problem, treatment regime, and prognosis for future athletic soundness.

"The clinical examination is always the starting point," says Mark J. Martinelli, DVM, PhD, Dipl. ACVS, Associate Surgeon (Orthopedics) at the San Luis Rey Equine Hospital in Bonsall, Calif. "Palpation of the musculoskeletal system will detect the aforementioned signs of joint disease, such as heat, swelling, and pain. The physical examination is usually followed by a lameness examination in order to identify which limb or limbs are affected. This phase may be carried out in hand, on a longe line, or even under saddle. In addition, flexion tests of joints may be carried out in an effort to localize the soreness further."

"Once a gait deficit has been identified in a specific limb, regional anesthesia is often performed to pinpoint the exact location of the lameness.
Regional anesthesia involves injecting a local anesthetic agent into a joint or surrounding nerves that supply a specific joint. If the gait deficit or lameness disappears, then the definitive location of the problem is determined. For instance, if lameness in the left forelimb disappears after injecting local anesthetic into the fetlock joint of that limb, then the fetlock joint is the location of the problem."

Next, Martinelli radiographs the affected joint. "Radiographs highlight the bone abnormalities seen with joint disease, such as osteophytes (bone spurs), sclerosis (denser than normal bone), lysis (softer than normal bone), and joint space narrowing," Martinelli continues. "These changes usually take time to develop, and therefore may not be present in the early stages of joint disease. When they are visible, however, radiographic changes clearly indicate that the joint is not normal. Conversely, nuclear scintigraphy (bone scan) is a sensitive imaging modality that will detect early changes in the bones around a joint. Because it is a metabolic imaging tool, it relies on living and changing properties of bone to produce an image. Therefore, even the most subtle bone abnormalities can be detected. Numerous studies in humans and other species have implicated hardening of the subchondral bone (bone beneath the cartilage of a joint) as the earliest stage of joint disease. If this is also true in the horse, then nuclear scintigraphy is clearly the imaging modality of choice to identify these incipient signs."

Although routinely employed in the diagnosis of joint disease, neither of these imaging modalities can help visualize the articular cartilage. "The challenge with traumatic arthritis is to determine the degree of cartilage damage," states McIlwraith. "Currently, the only way of completely assessing the cartilage in early osteoarthritis is with diagnostic arthroscopy (inserting a small instrument to visually inspect the joint). However, at CSU investigators have recently developed markers that are antibodies specifically made against breakdown products in the articular cartilage. Their usefulness in diagnosing early cartilage damage (which means early specific treatment) looks very promising."

Treatment of Joint Disease

One of the most successful approaches in treating joint disease, says Black, is with intra-articular medication - the direct administration of a drug into a joint. If done correctly, he maintains, intra-articular injection is a safe way to treat joint disease.

Black underlines the safety aspect by saying, "In a recent six-year period, 6,465 injections have been conducted at Pioneer Equine Hospital with no infections or significant joint reactions."

That doesn't mean that other approaches, such as intravenous and intramuscular injections, are not used. They can be combined with intra-articular injections.

The drugs used most often for the treatment of non-infectious joint conditions, says Black, include polysulfated glycosaminoglycans (PSGAGs), sodium hyaluronate, and corticosteroids.

Glycosaminoglycans--PSGAGs can be administered either intra-articularly or by intramuscular injection. "The most widely used PSGAG today is Adequan," Black says. He uses intra-articular injections weekly for three to five weeks. If the drug is administered intramuscularly, he gives it every three to five days for a minimum of four weeks.

The PSGAGs, says Black, can combat elements within the joint that cause inflammation. Studies have shown that PSGAGs stimulate the production of natural hyaluronic acid.

There are advantages and disadvantages to the PSGAG approach. The advantages, according to Black, include beneficial anti-inflammatory effects and chondroprotection (protecting the ends of the bones). These positive effects, Black feels, make this the drug of choice for Type 2 or 3 traumatic joints with damage to the articular cartilage.

Black says disadvantages include a risk of intra-articular reactions unless one also administers appropriate antibiotics, such as amikacin. The antibiotics would be administered at the same time via intra-articular injection. Another disadvantage of PSGAGs is cost. Maintaining a horse on the recommended therapeutic levels, Black says, can result in "significant cost to the owners." Sodium Hyaluronate - Sodium hyaluronate (also called hyaluronic acid, or HA) is the most recent class of anti-inflammatory medication to be used in the equine joint, says Black. This group of therapeutics, he says, provides significant lubrication to the synovial membrane that is responsible for dissipating more than 50% of the friction within the joint. Sodium hyaluronate counteracts metalloproteinases, prostaglandin E2 (involved in several inflammatory processes including the perception of pain), and free radicals.

"A synthetic form of sodium hyaluronate--Legend--has been developed that can be administered intravenously or intra-articularly," Black says. "When given intravenously, Legend has proven to have positive anti-inflammatory effects on the synovial membrane of the traumatized joint, and it has the advantage of offering the veterinarian a method for treating multiple joints with a single injection." Intravenous sodium hyaluronate is given weekly for three to four injections, usually followed by a decreasing number of injections for maintenance.

The intra-articular injection of sodium hyaluronate can be repeated in two to three weeks, depending on the severity of the joint inflammation. This would be followed by repeat injections as needed for maintenance of joints that have degenerative arthritis. "Many practitioners," Black says, "will begin the sodium hyaluronate series with an intra-articular injection followed by a series of two to three weekly intravenous injections. The intravenous form of HA can then be used for maintenance by administering Legend bi-weekly, monthly, or before major competitions."

"It should be recognized that HA is only effective against mild to moderate synovitis, and consequently corticosteroids are often used in conjunction with HA," says McIlwraith. The drug has been proven safe, with few side effects or injection reactions.

Corticosteroids - For some time, corticosteroids were the bad boys on the block. Many thought that injecting a joint with corticosteroids was giving the joint a death sentence. Yes, it would almost immediately reduce the inflammation, but in the long run it would have such a deleterious effect that the horse could wind up a cripple. Research at CSU has challenged that theory, and some corticosteroids have once again taken their place as part of the treatment regime for joint disease.

"Corticosteroid preparations," Black says, "are often categorized by duration of action, with the medium- or long-acting products usually favored over the short-acting due to the decreased treatment frequency. The three preparations favored at our clinic all have different duration of action and are used accordingly." "Methylprednisolone acetate (MA, a corticosteroid) has a long duration of action and tends to be used in lower motion joints, such as the distal tarsal joints or the pastern joints for degenerative joint disease or soft tissue arthropathies (joint disease)," says Black.

McIlwraith adds, "CSU research has shown that MA did have deleterious effects on the articular cartilage. This medicine should be used with caution."

"Triamcinolone acetate (TA) is a potent medium-duration steroid favored in higher motion joints at low dosages," says Black.

McIlwraith continues, "In contrast to the negative effects of MA, work at the CSU Orthopedic Research Laboratory has shown that TA not only had no negative effects, but that it promoted synthesis of essential elements of the articular cartilage. It also appears to be chondroprotective (protecting the cartilage)."

"Betamethasone phosphate is used routinely at our clinic to reduce synovitis and joint inflammation in the young, immature equine athlete," adds Black. "It, too, is a potent anti-inflammatory, but of short duration."

McIlwraith adds, "A study with betamethasone esters showed that they had no deleterious side effects."

Included in the advantage category for corticosteroids, says Black, is the fact that they are the most potent and cost-effective joint therapy available. Black doesn't shy away from the fact that there is potential danger when corticosteroids are used. One side effect of corticosteroid use outside the joint is laminitis if it is used incorrectly at improper doses, Black adds. An effective approach, Black says, involves combining corticosteroids and hyaluronic acid and administering this combination intra-articularly. The combination, he believes, provides maximum anti-inflammatory response as well as providing additional lubrication to decrease friction.

Other treatment methods include physical therapy and conditioning programs to slowly adapt the joints to stress rather than going straight from no work to heavy training. Phenylbutazone, ice, and cold water therapy are often used first on a joint problem before owners call the veterinarian.

"Nutraceuticals and other oral joint supplements are commonly used, but since they have been much less well studied than joint injections, it's hard to draw conclusions about them at this stage," says McIlwraith.

Take-Home Message

The message to horsemen is that athletic events of all kinds take a toll on a horse's joints, and it is the owner's responsibility to constantly monitor the horse's well-being. When that monitoring indicates joint trouble is brewing, a veterinarian should be consulted immediately. And if joint disease has already set in, it behoves the horse owner to allow the administration of appropriate therapy to combat the problem.
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