Coping with Arthritis in Horses
Arthritis is an unwelcome diagnosis for any horse, regardless of his discipline or occupation. Whether the condition appears suddenly after trauma or gradually with worsening stiffness, it means the same thing: Chronic inflammation has led to permanent degradation of the cartilage in a horse’s joints.
And the damage is irreversible: “The reality is that you’re not going to fix the joint or cure arthritis,” says Margaret Brosnahan, DVM, of Oklahoma State University. “Your goal is to reduce the inflammation, pain and further damage.”
Dire as that sounds, however, current research is yielding new treatments and investigating management techniques that can help horses work longer and live more comfortably with arthritis. Here’s an overview of how arthritis develops, how it can be managed and the treatments available for it.
A Cascade Effect
A horse’s knees, hocks and pasterns are designed to flex, compress and extend hundreds or thousands of times each day, for years on end--all while supporting his weight and enduring concussive forces.
Joints have several components: collateral ligaments, which prevent lateral movements of the bones; synovial fluid, which fills the space between the bones and provides lubrication and nourishment to the cartilage; the joint capsule, which stabilizes the joint; the synovial membrane, which regulates the joint fluids; and the articular cartilage, the soft structural tissue that covers and cushions the ends of the bones where they meet.
The cartilage is a framework of tissue made up of collagen fibers, which give the structure its strength. The collagen is interlaced with proteoglycans--long, protein-based molecules with negative charges that trap water within the matrix. As the joint flexes, the cartilage compresses and expands, forcing water in and out of the spaces, which helps to provide a shock-absorbing effect.
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“Collagen is like the cotton in your clothes,” says David Frisbie, DVM, PhD, DACVS, of the Equine Orthopaedic Research Center at Colorado State University. “Take a wad of intricately laced cotton, put it in water, and it will soak it up like a sponge. Press down and it will expunge it out and then refill again. That’s how cartilage works. The collagen is the framework, and the proteoglycans are stuck in the collagen to keep the sponge full and the water interspersed.”
As a horse moves, the flexing and compression can produce minute damage within the joint structures that triggers mild inflammatory responses to make the repairs. Normally, the body’s own defenses control inflammation and the joint remains healthy and sound.
Sometimes, however, the inflammatory process overwhelms the body’s ability to contain it, either from a single acute injury or from many years of use. At that point, a cascade of events begins: The inflammatory enzymes break down the lubricating synovial fluid, which gets thinner. Proteoglycans are lost and the collagen fibers lose integrity, which diminishes the cartilage’s ability to retain lubricating water. This damage stimulates even more inflammation, which fills the joint capsule with fluids, leading to pressure, pain and stiffness. The buildup of inflammatory enzymes further breaks down the synovial fluid, which leads to more damage to the cartilage.
“Left unchecked, a lot more degeneration can occur because the inflammatory response keeps triggering a loss of proteoglycans and collagen. It’s a bad cycle at work,” says Frisbie. “This is how an acute injury can cause progressive damage.” Eventually, the cartilage can tear or erode away entirely, leaving the exposed ends of hardened bone to rub against each other. This is a painful, advanced case of osteoarthritis, also called degenerative joint disease.
The Challenge of Diagnosis
The key to helping a horse live comfortably with arthritis is to catch it early and get the inflammation under control to stop the cycle of damage. But in most cases, by the time a horse is lame, the arthritis is already advanced.
That’s why it’s important to investigate even minor discomfort. Some horses show early signs of arthritis in their way of going: They’ll move stiffly until they’ve warmed up, or they may be perpetually short-strided. Others may be reluctant to move only on one lead, or in one direction, or at a certain gait--signs that are especially significant if these movements were previously performed with ease. Sometimes developing arthritis causes a sour attitude or resistance to rider aids.
A veterinarian will begin the diagnostic process with a hands-on examination to look for heat and swelling in a horse’s joints, followed by a full lameness exam, including flexion tests. Nuclear0 scintigraphy can detect subtle early changes that indicate injury within the bones; X rays will show the more significant changes associated with more advanced arthritis. Arthroscopy--the insertion of a fiber-optic “camera” directly into the interior of the joint--is the best way to diagnose lesions in the cartilage.
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