Arthritis or inflammation of the joint is a common canine and human orthopedic problem. The term arthritis is a broad term and can be broken down into several forms and many sub-components. Examples of different forms of arthritis include infectious, immune mediated and osteoarthritis (OA).
Osteoarthritis is the most common form of arthritis in dogs and humans. Osteoarthritis involves joint capsule inflammation, joint capsule thickening, joint fluid accumulation, joint swelling, bone spur formation and most importantly, cartilage wear and tear. Hyaline cartilage covers the ends of long bones and is found in all motion joints. Hyaline cartilage is slick, with very low friction allowing joints to move smoothly. Hyaline cartilage also acts as a joint shock absorber. In cases of severe OA the hyaline cartilage can wear away exposing underlying bone. This degenerative wearing away results in what is know as “bone on bone” and is the most devastating aspect of OA. (It’s the reason so many humans end up with knee replacements.)
Primary versus Secondary Osteoarthritis
In humans two forms of OA exists; primary and secondary. Primary OA occurs over time without a specific underlying cause. Secondary arthritis, as the name implies, is secondary to some form of abnormal joint anatomy. For the most part, DOGS DO NOT DEVELOP PRIMARY OA. Almost all dogs with OA have some underlying anatomical problem resulting in secondary OA. For example, dogs with hip arthritis always have a mal-formed hip joint or hip dysplasia. Dogs with knee or stifle arthritis almost always have an ACL tear or patellar luxation. The bottom line is DOGS RARELY DEVELOP OA WITHOUT AN UNDERLYING CAUSE.