Osteoarthritis is a chronic and progressive disease that occurs due to the wearing down of joint cartilage and the formation of new bone at the joint surfaces and margins.
Osteoarthritis is the most common form of arthritis in dogs and cats. It has been estimated that approximately 20% of adult dogs are affected, and it has been reported that more than 60% of adult cats show radiographic evidence of the disease.
Osteoarthritis should be thought of as a disease process rather than a disease entity because it appears to be a common final pathway for the failing joint. In dogs, it almost always occurs secondary to an initiating abnormality, such as joint laxity (hypermobility) or instability, osteochondrosis (an abnormal development of the cartilage on the end of a bone in the joint), or trauma.
Classification
Osteoarthritis can be classified as primary or secondary.
In dogs, the disorder most frequently occurs secondary to an identifiable abnormality of the joint, such as a developmental disorder, joint instability, or trauma (e.g., osteochondritis dissecans - when a piece of bone and the attached cartilage breaks down and becomes loose, hip dysplasia - a genetic condition that causes abnormal development of the hip joint, or cruciate ligament rupture).
In cats, this may also be the case (e.g., hip dysplasia), but often in cats, no initiating cause can be identified.
Causes of osteoarthritis
The cause of osteoarthritis in a particular joint may be challenging to identify.
Factors to take into account include genetics, age, and systemic factors such as obesity. Genes that control the susceptibility to osteoarthritis have not yet been identified in dogs, although there have been developments in understanding the genetic basis of diseases that cause secondary osteoarthritis.
Diagnosis and Staging of Osteoarthritis
In dogs, osteoarthritis is often secondary to another joint abnormality (e.g. instability, laxity or fracture). Idiopathic (or spontaneous) osteoarthritis is diagnosed when attempts to identify an initiating cause have failed.
Osteoarthritis often is not a diagnosis of sufficient accuracy in canine orthopedics because the disease is usually secondary and is the result of some other primary joint abnormality (e.g., instability, laxity, fracture). Idiopathic osteoarthritis is diagnosed when all attempts to identify an initiating cause have failed.
Different methods may be used to assist diagnosis, including orthopaedic exam, radiograph, CT or MRI and synovial fluid analysis (the thick, viscous liquid that lubricates and protects your pet’s joints).
Signs of arthritis in dogs
Signs of disease include:
- Reluctance to exercise
- Inactivity stiffness
- Lameness
- Inability to jump (up or down)
- Behavioural changes, such as aggression
These signs can vary from very mild and intermittent to severe and persistent, depending on multiple factors, including:
- Breed
- Your pet’s usual demeanor
- The stage of the disease
- The joint affected
Most signs will gradually worsen, although this can happen at a varying rate, sometimes interspersed with periods of remission and flare-ups of the disease.
Signs of arthritis in cats
Cats with osteoarthritis may show very few signs to their owners, but may typically exhibit:
- A reduction in activity
- Reluctance to jump
- A reduction in maximum jump height
- An unkempt appearance
- Aggression
Management of Osteoarthritis
Management of osteoarthritis is most often conservative and uses different methods of treatment. A vast majority of cases are managed with NSAIDs (non-steroidal anti-inflammatory drugs), combined with nutritional recommendations, weight control and exercise management.
Medical Management of Osteoarthritis
Drugs for the treatment of osteoarthritis can be classified as symptom- or structure-modifying agents. The former category includes medications designed to treat the pain associated with osteoarthritis, and the latter category includes medications designed to slow, stop, or reverse the changes that occur in the affected joint(s). Many symptom-modifying medications are available for use in canine osteoarthritis, and a restricted number are available for feline osteoarthritis.
Nutritional Management of Osteoarthritis. Nutritional supplements can be delivered in two forms: nutraceutical or functional food.
A nutraceutical is effectively any substance that is a food or a part of a food that provides medical or health benefits, including the prevention and treatment of disease.
Examples of nutraceuticals include the chondroitin sulfate, glucosamine sulfate, and glucosamine hydrochloride; essential fatty acids, particularly n-3 polyunsaturated fatty acids; and antioxidant sugars (vitamin C). These supplements may also be incorporated into functional foods to be delivered as complete diets for dogs and cats.
Mesenchymal Stem Cell Therapies for Osteoarthritis. In the past decade or so, there has been a surge of interest in the use of mesenchymal stem cells to repair damaged connective tissue. This discipline, known as regenerative medicine, aims to develop biologic, cell-based therapies to repair or replace injured or eroded tissues such as cartilage.
Surgical Management of Osteoarthritis.
Although most dogs and cats with osteoarthritis are managed using a combination of medical and other conservative measures, those living with severe effects of osteoarthritis may need surgery.
Joint debridement and micropick surgery. Used in the treatment of moderate osteoarthritis. The aim of such surgeries is to stimulate fibrocartilage repair mechanisms.
Joint replacement. Often, the ideal surgical treatment for osteoarthritis would be joint replacement with a prosthetic joint, but this option is available only for a limited number of patients. Total hip arthroplasty is now a common procedure in specialist practices with reportedly very good success rates.
The elbow joint is a more complex joint than the hip joint, and at the current time, functional improvement following total elbow replacement is not absolute. Nevertheless, for carefully selected candidates, total elbow replacement may be a suitable option.
Total knee replacement for dogs is another innovation. The numbers of patients receiving this procedure so far are relatively small.
Arthrodesis and salvage procedures. For some joints with severe pain that haven’t responded well to medical management, arthrodesis (joint fusion) may be considered. This option is best suited to low motion joints but can be performed on most joints with variable effects on functional performance. Dogs tolerate arthrodesis of the shoulder joint, carpus, and tarsus reasonably well. However, arthrodesis of the elbow or stifle joint (comparable to a human knee) is typically not tolerated as well.
For a hip joint where pain is severe in pets that cannot receive a total hip arthroplasty, whether this be on clinical or economic grounds,
For the intractably painful hip joint that cannot receive a total hip arthroplasty on clinical or economic grounds, excision arthroplasty may be considered. This is a surgical procedure that involves removing joint surfaces to allow for motion and function.