Clean Run Magazine - May 2007 - 62

Focus on Canine Sports Medicine Joint Protective Agents for Performance Dogs By Sherman O. Canapp, Jr., DVM, MS, Diplomate ACVS, and Debra A. Canapp, DVM, CCRT, CVA (pending) D egenerative joint disease (DJD) also known as osteoarthritis (OA), or simply arthritis is a debilitating disorder affecting a wide range of animal species and humans. Canine OA is a common cause of joint failure with stiffness, loss of mobility, and varying degrees of inflammation and pain. DJD is commonly caused by joint instability due to slack/lax ligaments; it can also result from strains, direct or indirect injury, and from faulty bone and cartilage development. Less efficient repair processes in the older animal make age a contributing factor, and the condition may be exacerbated by obesity and/or overexertion. Once joint cells are stressed or damaged, enzymes are released that fray and ulcerate joint cartilage and that attack the lubricants of the joint fluid. As a result of the damage, the joint lining and capsule become inflamed and the bone underlying the cartilage less resilient. Only when these sensitive tissues (both capsule and bone) are affected, often after significant articular cartilage damage, can we then see the clinical signs of pain, swelling, and stiffness. Articular cartilage is found in all moving joints in the dog’s body (synovial joints) and its role is to protect the bones by keeping the surfaces of the bones apart from each other, to absorb shock, and to help make movement smooth. Articular cartilage does this by providing a protective, wear-resistant surface to the end of the moving bones. Normal articular cartilage, by its rubberlike resiliency, functions to reduce pressure, and where it covers the end of a bone, its smooth surface minimizes the friction effect of shearing forces. Cartilage in the joints derives its nutrition from the movement and contact pressure of the joint. This movement and pressure helps transmit nourishment from the joint fluid to the cellular matrix of the cartilage. Articular cartilage is composed of chondrocytes and extracellular matrix. Chondrocytes are a cell type found in articular cartilage. Chondrocytres take an active part in the synthesis of and turnover of the extracellular matrix and the replacement of degraded matrix and its components. Extracellular matrix has two main components, tissue fluids and proteoglycans. Tissue fluids are mostly composed of water but also contain gases, small proteins, metabolites, and a high concentration of cations to balance the negatively charged proteoglycans (the second component of the extracellular matrix). Chondrocy tes and the mat r ix are interdependent on each other for maintenance. Chondrocytes secrete the macromolecules that make up the matrix and the matrix in turn protects the chondrocytes from mechanical damage, helping them to maintain their shape. Synthesis and degradation of matrix molecules by chondrocytes is a continuous process throughout life. The precursor lesion of osteoarthritis, namely chondromalacia, or softening of the cartilage, is observed to occur first in non-loadbearing areas of the joint. Articular cartilage injuries are common. The normal structure and function of articular cartilage can be upset relatively easily and damage to the articular cartilage often results. There are several ways in which your or your dog’s articular cartilage can be damaged. • A sudden direct blow to the cartilage (traumatic), namely a high-energy injury, such as a bad fall directly onto your knee, or an injury during sporting activities • Slow damage to the cartilage following a knee injury (post-traumatic) • Wear and tear over time (degenerative joint disease or DJD) especially when there is malalignment or instability in the joint and/or if the dog is overweight >Diagnosis The beginning stages of OA are not readily apparent, but, once the deterioration has reached the synovial membrane and/or the bone beneath joint cartilage, painful inflammation begins. The first visible sign of osteoarthritis pain may come in the form of a limp, sensitivity to touch in a certain area (for example, along the spine), a decrease in activity, stiffness (especially after rest), difficulty getting up, lying down, or climbing stairs, or an inability to jump. Evidence of OA has been found in the fossils of prehistoric dinosaurs as well as in the joints of ancient mummies. It is unfortunate, however, that despite the long existence of this disease, the facts concerning specifically how OA is formed and the factors triggering its development are still incompletely known. It has been reported that OA may affect up to 20% of the canine population over one year of age. Studies have shown that nearly 50% of musculoskeletal disorders identified over the last 10 years in 16 veterinary hospitals were due to joint disease. To date there have been no studies specifically looking at the rate of osteoarthritis found in performance dogs. Theoretically we 62 Clean Run | May 07

Clean Run Magazine - May 2007

Table of Contents for the Digital Edition of Clean Run Magazine - May 2007