You know what arthritis is, but how and why does it actually occur, and what happens inside the affected joint? Here’s a close- up look at the pathology of this common disease and how it affects dogs and cats.
We all know someone with arthritis, whether it’s a human friend or family member, or an animal companion. But if asked to describe what goes on inside an arthritic joint, many of us would be lost for words. We know it hurts, but we don’t really know why or how it happens.
Dogs and cats have an intricate skeletal system made of bones, muscles tendons and ligaments. The joints are the hinges that allow the skeleton to move and flex in amazing ways. They’re composed of cartilage over the bone ends and are stabilized by tendons and ligaments. The cartilage is a smooth but tough and protective coating for the bones underneath. It absorbs shock and reduces friction. The synovial tissue encloses the joint in a joint capsule and the synovial or joint fluid adds to the cushioning effects and provides lubrication for smooth joint action. When joints are damaged by disease or injury, inflammation results. Inflammation in the joints is known as arthritis. It may be either degenerative or inflammatory in nature. Degenerative joint disease, or osteoarthritis, is more common in dogs than inflammatory joint disease.
How does osteoarthritis develop?
With osteoarthritis, changes that occur in the cartilage cause damage in the underlying bone. The cartilage provides a cushion for the bones of the joint during movement and prevents them from rubbing or hitting each other. But if it becomes dried or chipped, the underlying layer of cartilage-producing cells is exposed. These cells lose elasticity and begin to degenerate, and the cells that make up the cartilage matrix decrease.
Enzymes are released that damage the cartilage and thin the synovial fluid, greatly reducing its lubricating properties. The bones are exposed and the articular surfaces rub together, causing further damage and interfering with the joint’s normally smooth movement. This leads to joint instability. The joint fluid increases further and the joint space is filled with thin fluid and degenerating cartilage debris. The animal’s body responds by sending white blood cells to the affected joint. These cells release enzymes that cause inflammation and swelling or effusion in the joint. This causes stiffness and pain.
Unfortunately, since the joint cartilage does not contain any nerves, considerable damage and thinning of the synovial fluid has to take place before degenerative joint disease manifests itself. The remodeling and inflammatory changes create pain and decrease the mobility of the affected joint. Muscle atrophy results from the disuse of the painful limb. Pain and discomfort result in lameness that may be more noticeable first thing in the morning or upon rising.
Osteoarthritis is a progressive disease that gets worse as more and more of the cartilage in the joint dies. When the cartilage has all degenerated, then the sensitive bone (which does have innervation) is exposed. This is an extremely painful situation and the animal will be lame by this stage.
Causes of degenerative joint disease
Osteoarthritis is the most common form of arthritis in dogs and can be divided into primary or secondary arthritis.
Primary osteoarthritis is due to an inherited predisposition towards the problem. An example would be hip dysplasia in certain lines of German shepherd. These dogs are predisposed because their inherited anatomical conformation puts excessive stress on the hip joints.
Secondary osteoarthritis results from wear and tear on the joint. This can be abnormal stress on normal joints, or normal stress on abnormal joints. Vigorous exercise, excessive jumping, injuries, accidents or stretching and tearing ligaments can lead to arthritis due to abnormal stresses on previously normal joints. Large breed dogs are more susceptible to osteoarthritis due to increased weight and stress on the joints. Dogs who are overweight, senior, working or have medical conditions such as diabetes are also at an increased risk of osteoarthritis.
Osteoarthritis or degenerative joint disease is also seen in cats. In a recent study, it was found that 90% of cats over the age of 12 had radiographic evidence of degenerative joint disease. Clinical signs of arthritis in cats can be a reluctance to use the litter box, poor grooming habits, decreased appetite, weight loss, depression, neurological signs and lameness. Many cases of arthritis are idiopathic in nature.
Focus on inflammatory arthritis Inflammatory
joint disease can be caused by infections (septic arthritis) or immune mediated disease. Diagnosis is critical for both these types of arthritis. Inflammatory arthritis is usually accompanied by systemic illness such as fever, loss of appetite and painful movement. Generally, multiple joints are involved.
Infectious joint disease can be caused by bacteria, tick borne diseases (such as Lyme disease) or fungal infections. These organisms and the body’s response to them damage the joint and the cartilage.
Immune mediated arthritis can be caused by an underlying immune deficiency or problem. It results from the body attacking itself. Rheumatoid arthritis and systemic lupus are two types of inflammatory arthritis, neither of which is very common in animals.
How it arthritis diagnosed?
Radiography of the bones and joints can confirm degenerative joint disease that had been diagnosed based on clinical signs. In cases of suspected infectious or immune arthritis, a joint fluid analysis may be needed. Special blood tests may also be needed to diagnose conditions such as tick borne arthritis and lupus.
Learning something about the pathology of arthritis and its causes will help you determine when your companion animal might be starting to suffer from the disease and is in need of a veterinary diagnosis and treatment. A little education on your part can mean a long, healthy and painfree life for your best friend!
Treatment and prevention Treatments for arthritis are varied but focus on reducing pain and improving mobility.
• Pharmaceutical treatments can include steroids, non-steroidal anti-inflammatory drugs, polyglycosaminoglycans (drugs that prevent cartilage breakdown) and painkillers.
• Surgical treatments may be necessary for some conditions.
• More natural treatments include glucosamine, Omega 3 fatty acids, dietary therapy, acupuncture, laser or magnetic therapy, herbal treatments, chiropractic, massage and physiotherapy including water therapy.
• Weight loss and exercise are extremely important for any arthritic animal.
A good healthy diet and proper exercise can help prevent arthritis or reduce its effects. Maintaining a healthy body weight and avoiding obesity are critical. Omega 3 fatty acids can help prevent the inflammation seen with degenerative joint disease. Supplements like glucosamine can also help prevent arthritis.