"Traumatic joint disease is the leading cause of lameness in horses--and it can happen to any horse at any time," said James Casey, DVM, MS, who runs an equine sports medicine and dentistry practice in Laurel, Md. "More than half of all equine lameness is due to noninfectious joint disease and injury. It can happen from one bad step, but it's most likely due to cyclic (repeated) trauma."
Casey discussed joint disease and lameness for a full house of 303 horse owners at the 2006 Healthy Horses Workshop, held in conjunction with the American Association of Equine Practitioners 52nd annual convention on Dec. 2 in San Antonio, Texas. His main point: Prevent joint disease rather than treating it once it has occurred.
"You don't wait until your car is completely broken down to get it fixed; you usually get oil changes and maintenance before it gets to that point," he recommended. "Think of veterinary medicine the same way."
For the racehorses he primarily treats, "We usually go through and inject joints as a preventive treatment before and during the seasons," he said. "Not every horse needs that, but if they're doing maximum performance, it helps maintain health in the joints."
Progression of Joint Disease
Casey discussed the structural and fluid components of joints before moving on to joint disease.
"Joint disease is a process. It starts with a little problem, then it snowballs," he said. "A little synovitis gets worse and leads to pain, which leads to reduced use of the limb, muscle atrophy, unequal forces (loading), more pain, etc. Predisposing factors include poor conformation and joint instability. We cause a lot of these problems ourselves with poor breeding, shoeing, footing, etc."
Inflammation is a key part of the joint disease process, Casey explained--it's a normal body function that leads to repair and wound healing. Thus, it signifies injury. White blood cells play a big role in this process. However, when the stimulus for inflammation is too strong, the inflammatory process itself causes damage to joints.
Casey described the progression of joint disease as follows:
"First, there's synovitis--the synovial membranes (which line the joint and produce synovial fluid to lubricate it) become inflamed and permeable. Then white blood cells gain access into the synovial fluid, burst, and release enzymes that break down hyaluronic acid (HA, a gel that lubricates and cushions the joint) and destroy its lubricant/barrier function. Eventually, these enzymes gain access to the articular cartilage (covering the ends of bones' joint surfaces) and the surface of the cartilage starts to fray because it can't repair as fast as it's damaged. Once the articular cartilage is impaired, it can no longer provide equitable distribution of forces or compliance. The subchondral bone that lies directly underneath the protective cartilage now can't take shock forces, and you end up with bone fractures (joint chips, or maybe bigger fractures).
"Degenerative joint disease becomes a vicious cycle," he added. "When full-thickness loss of cartilage occurs, this is permanent."
Watch for the Signs
"Once you see something (joint pathology) on a radiograph, you're a long ways down the road with this problem," Casey cautioned. "We need to try to interrupt the process earlier. Notice subtle differences in the way the horse moves and how aggressively he trains. If you see a change, call your veterinarian. He/she can perform a physical exam and also may perform a synovial fluid analysis of the affected joints. The synovial fluid's thickness and consistency is an indication of a joint's health."
He also recommended that owners watch for the cardinal signs of inflammation around joints: heat, pain, swelling, redness, and loss of function.
"Digital radiographs, infrared thermography, and MRI (magnetic resonance imaging) can all help diagnose causes of a joint problem," he went on. "One thing to keep in mind is if you've got something wrong in one place, the horse is often sore in other places, too. If he's sore in a hind limb, he might be sore in his back (from carrying himself differently to compensate for the sore area)."
Treating Joint Disease
"There is no set treatment regimen for affected horses," Casey said. "You can go a long way by maintaining proper body weight for that horse, modifying his shoeing, and/or modifying his activity level. Some horses may benefit from a dose of Bute (phenylbutazone) before and after strenuous activity. And rest is always a part of treatment; it relieves use trauma and allows inflammation time to subside and damage to heal. Ask yourself: When it comes to treating your horse, do you just want to patch him up for the pain, or heal him?
"Unfortunately, rest by itself is not enough, so we might add physical therapy, cold hydrotherapy, acupuncture, ultrasonography, shock wave therapy, hyperbaric oxygen therapy, and/or surgery to remove fragments, stabilize intra-articular (within a joint) fragments, lavage (wash out) the joint, or employ therapeutic joint injections," he said.
The goals of treating traumatic and degenerative joint disease are as follows, he said:
- Alleviate the immediate effects of inflammation, including pain and reduced function.
- Prevent the development of permanent fibrosis in the joint capsule (as a result of uncorrected inflammation), which in turn can cause decreased shock absorption in the joints.
- Prevent or minimize the development of osteoarthritis.
- Normalize the inflamed joint(s) as quickly as possible before permanent damage occurs.
Corticosteroids are a good thing when used properly; they are the most powerful anti-inflammatory in our arsenal for joint disease. They work by stabilizing the membrane and keeping white blood cells out. There are several choices of medications; some are more potent or longer-acting than others.
Potential side effects include delayed healing and decreased resistance to infection. When corticosteroids are used properly, the benefits outweigh the risks, he noted.
Non-steroidal anti-inflammatory drugs (NSAIDs) include phenylbutazone (Bute) and flunixin meglumine (Banamine). "I always give a little Bute or Banamine at the same time (when giving joint injections)," he commented. "And Surpass (diclofenac sodium, a topical NSAID) is good for certain things, but it doesn't go real deep."
Hyaluronic acid is anti-inflammatory; it inhibits a type of prostaglandin that affects joints, toxic oxygen radicals, and cell migration. It also lubricates the joint, helps restore the function of HA that has been lost due to inflammation, and improves endogenous (caused by factors inside the organisim) HA production. Use it for mild to moderate synovitis, and keep in mind that higher molecular weight is better.
Polysulfated glycosaminoglycan (PSGAG) is a small molecule that can actually infuse into the cartilage. It acts as a building block for healing joint disease. "It's referred to as a DMOAD (disease-modifying osteoarthritic drug)," Casey noted. "It inhibits enzymes from breaking cartilage and synovial fluid down further and stimulates both collagen synthesis and production of hyaluronic acid." PSGAG (Adequan) is available in two forms, intramuscular (IM) for systemic use and intra-articular for direct joint injections.
Interleukin-1 receptor antagonist protein (IRAP) blocks bad interleukin (a mediator of inflammation) and allows good interleukin to work. It's a non-pharmacological approach that uses the horse's own materials to help him heal. (See www.TheHorse.com/ViewArticle.aspx?ID=6619 for more information.)
TILDREN, or tiludronic acid is not approved for use in the United States, but your veterinarian can get permission to import this drug. It inhibits bone reabsorption. It has been effective for navicular syndrome and is similar to a drug women take to inhibit osteoporosis.
"The main thing I want you to take away from here is this: Don't let a horse break down before you fix him," said Casey. "Work on him in between times, keep him shod properly, maybe use joint injections as needed. Treat him like your car, take him in for maintenance." It might cost money to inject his joints, he said, but that's a lot cheaper than surgery later or not being able to use the horse.
The "Joint Disease and Lameness in Horses" PowerPoint presentation shown at the Healthy Horses Workshop may be viewed on Casey's Web site: www.equinehorsevet.com/jmc-faqs.htm (12.9 MB).