You may have heard of it, but do you really know what it is? Affecting around 20% of dogs over one year old, 60% of cats over six, and 90% of dogs over twelve, osteoarthritis may well become part of your four-legged friend’s daily life one day. Which structures does it affect? How and why does it develop? How can you spot it? Find the answers to your questions.
The Structure of a Joint
A joint consists of all the soft tissues (such as ligaments and the joint capsule) and hard tissues (bone and its cartilage) that connect two or more bone ends.
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These joints largely ensure the mobility of our skeleton. They are stabilized by muscles and their tendons, ligaments, and—to a lesser extent—by their joint capsule, which contains synovial fluid. This fluid is produced by the synovial membrane and contributes to joint lubrication as well as cartilage nutrition.
Mostly composed of water and cells (called chondrocytes), all held together in a collagen and proteoglycan framework, cartilage absorbs shocks and facilitates smooth bone movement.
A Vicious Cycle
Osteoarthritis is a degeneration of joint structure. This chronic and irreversible disease progresses through painful flare-ups. It causes inflammation in the affected joint and, at an advanced stage, stiffness, muscle loss, and reduced mobility.
This condition begins with the erosion of the collagen framework, the superficial layer of cartilage. As the erosion progresses, it loses its properties, significantly affecting compression resistance. Chondrocytes, in attempting to repair the damage, produce inflammatory molecules that escape from the erosions, bathe in the synovial fluid, and accumulate in the joint. A cascading inflammation then sets in and gradually spreads, affecting the various structures of the joint. Additionally, an imbalance between cartilage and subchondral bone synthesis and degradation develops, leading to both bony outgrowths (osteophytes) and areas of erosion.
Trauma to a joint, a chronic inflammatory disease (such as that caused by excess weight or obesity), a developmental disorder in young individuals, an infectious disease, repeated stress, or simply the natural aging of the joint: the causes of osteoarthritis are numerous, yet identifying them is not always straightforward.
Symptoms Not Always Obvious
Arthrosis develops slowly and silently. Initially, the signs are subtle and inconsistent. Your four-legged friend may simply seem to have mellowed. As inflammation and damage set in, they become reluctant to chase their ball or join you on the couch. One day, they may even hesitate to go for a walk or struggle to get out of their bed—or even groom themselves.
Detecting osteoarthritis isn’t easy, then—and this is especially true for cats, which rarely show signs of joint pain, even in advanced stages.
Sources:
Radiographic Evidence of Degenerative Joint Disease in Geriatric Cats: 100 Cases: This study published in the *Journal of the American Veterinary Medical Association* aimed to determine the prevalence of radiographic signs of degenerative joint disease in cats over 12 years of age.
Understanding Osteoarthritis Pathophysiology: This literature review examines the physical, enzymatic, and molecular changes occurring in pets affected by osteoarthritis.
