Causes of Canine Arthritis
Joint inflammation and pain, commonly called arthritis, can be classified as degenerative (non-inflammatory or traumatic) or inflammatory. While this nomenclature can be confusing, because all joint disease involves inflammation, the primary cause of degenerative joint disease is not inflammation, while the primary causes of inflammatory arthritis is. Inflammatory arthritis can be further categorized as infectious or immune-mediated (sterile) in nature.
Degenerative Joint Disease (DJD)
Degenerative joint disease, also called osteoarthritis or OA, is one of the most common types of arthritis seen in dogs. It is a noninflammatory, slowly but inevitably progressive and irreversible syndrome in which the articular joint cartilage deteriorates. Degenerative arthritis can be further classified as primary or secondary meaning it is attributable to some other predisposing injury or condition.
Primary degenerative arthritis is uncommon. Most of the time, this form of arthritis develops secondary to some other inciting event, such as acute or chronic joint trauma. Injury to a joint – especially to the articular cartilage connecting the bones of a joint - causes release of a number of chemical substances, collectively called inflammatory mediators. Inflammatory mediators break down the connective cartilage matrix more rapidly than it can be rebuilt and cause pain.
The initiating events that trigger the inflammatory cascade usually fall into one of two categories, either: 1) abnormal forces imposed on normal joints such as fractures, sprains, obesity, direct trauma, etc.; or 2) normal forces imposed on abnormal joints such as elbow or hip dysplasia, osteochondrosis dissecans (OCD), patellar luxation, ununited anchoneal process, fragmented coronoid process, cranial cruciate ligament rupture or tear, and other congenital or genetic conformational cartilage, bone or joint defects. Degeneration and gradual collapse of the joint space adversely affects the mechanical integrity of the joint and causes remodeling of bone beneath the cartilage. As the joint continues to degenerate, small painful, bony outgrowths develop, intensifying the dog’s pain.
Inflammatory Joint Disease
Inflammatory arthritis can be further categorized as either infectious or noninfectious. Joint infections can be caused by bacterial, fungal, viral or rickettsial organisms. Tick-borne diseases such as Rocky Mountain Spotted Fever, Lyme Disease and Ehrlichiosis can all cause joint pain. Septic arthritis can develop in joints that are inoculated with bacterial microorganisms through veterinary injections, bites, open or penetrating wounds or the blood stream. Fungal arthritis is uncommon in dogs.
Noninfectious arthritis is usually immune-mediated and frequently involves multiple joints. For some reason, the dog’s immune system starts making antibodies against its own joint surfaces. Immune-mediated arthritis can destroy articular cartilage and joint surfaces (erosive arthritis), leading to severe joint deformities. Rheumatoid arthritis is one type of erosive arthritis that can cause significant leg and foot deformities. Plasmacytic-lymphocytic synovitis and systemic lupus erythematosus are other immune-mediated diseases that cause erosive arthritis in dogs. Immune-mediated arthritis can also cause inflammation and discomfort without tissue destruction (nonerosive arthritis). The most common example of nonerosive arthritis in large and giant breed adult dogs is called idiopathic nondeforming arthritis. Its underlying cause is not known.
Regardless of cause, the ultimate effect of arthritis is the same: pain and loss of normal function of the affected joint.
Preventing Arthritis in Dogs
Because there are so many potential causes of canine arthritis, it is rarely possible to prevent it. Certainly, the progression of secondary degenerative arthritis may be delayed if it is identified early and if the predisposing cause is resolved. Weight management is probably the most important factor in preventing or delaying the progression of arthritis. Overweight dogs should be put on a calorie-restricted diet under a veterinarian’s strict supervision. A number of prescription and over-the-counter supplements are available to minimize arthritis pain; some of these may actually help prevent further joint damage. Owners should always provide their dogs with soft, comfortable, well-padded sleeping areas and should take reasonable measures to restrict jumping from high places and other activities that might lead to injuries. Regular, moderate, low-impact activities can strengthen the musculature surrounding at-risk joints.
Joints can be affected by environment, exercise, diet and weight. They can also be influenced by genetics.