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What is Arthritis?

Updated: Jun 26, 2023

Arthritis is the inflammation of a joint or joints, and the most common synonyms are osteoarthrosis (a pathological process distinct from acute inflammatory process), osteoarthritis (emphasizing the inflammatory nature of the condition), and secondary joint disease (where initiating factors have been identified, such as joint instability due to abnormal conformation, ligament rupture, or intra-articular fractures). Osteoarthritis, commonly known as a degenerative joint disease, is a common condition that mostly affects older or obese cats and dogs.

Osteoarthritis is a disease of joints that affects all of the weight-bearing components of the joint:

  • Articular cartilage

  • Menisci

  • Bone

In the general dog population, osteoarthritis prevalence ranges from 20% to 60%, with greater rates noted in specific breeds including Labrador Retrievers, German Shepherds, and Golden Retrievers. Additionally, the prevalence rises with age, affecting up to 80% of dogs older than 8 years.

Compared to dogs, cats have a prevalence of about 61% with cats older than 6 years having radiographic signs of osteoarthritis.

With arthritis, the cartilage that cushions the joints gradually wears away, resulting in pain, stiffness, and restricted movement. Since osteoarthritis in pets is a sequel illness to a developmental joint problem, many companion animals show symptoms at an early age. Osteoarthritis most often occurs at the ends of the toes, neck, shoulder, elbow, back (lumbar area), knees, and hips.

The most common locations for osteoarthritis in dogs include the knee, hip, shoulder and elbow, which are shown with their homologous equivalent in humans. The average lifespan of a large-breed dog is ~12 years, with a proportionately longer time spent in old age than in a typical human lifespan.

Overall, osteoarthritis poses a serious health risk to populations of dogs and cats, and its early diagnosis and treatment are essential to enhancing the quality of life for affected animals.

What are the causes and predisposing factors of osteoarthritis in pets?


Despite the fact that osteoarthritis is associated with developmental disorders and joint trauma, the root cause is multifaceted. Commonly it is acute on chronic presentation, referred to as as an " acute flare".

A quick and severe exacerbation of symptoms or a condition is referred to as an acute flare. It can occur in a variety of medical situations, including autoimmune disorders, chronic pain syndromes, and chronic illnesses like arthritis. A patient will suffer significant pain, edema, inflammation, and other symptoms of their illness during an acute flare. This abrupt worsening of symptoms frequently takes place without prior notice and may be brought on by a number of things, including stress, physical exercise, climatic changes, or exposure to specific chemicals.
Arthritis and joints inflammation. It affects hips and elbows causing lameness and stiffness.
Arthritis and joints inflammation. It affects hips and elbows causing lameness and stiffness.

  • Apparent sudden onset lameness

  • Lameness is generally in single or multiple limbs.

  • Often following inappropriate use/trauma to already diseased joint.

  • Consider soft tissue co-morbidities being the source of “acute flare”.

Certain breeds and species are predisposed to arthritis. Primary osteoarthritis is less likely to be influenced by aging or obesity while secondary osteoarthritis is more likely to be associated with developmental joint disease and trauma. Breeds predisposed to hip dysplasia, elbow developmental disease, osteochondrosis, patellar luxation, growth plate disorders and avascular necrosis of femoral head include Rottweiler, Dogue de Bordeaux, Old English Sheepdog, Border Collie, Bull Mastiff, German Pointer, German Shepherd Dog, Golden Retriever, Labrador Retriever, Scottish Collie, English Springer Spaniel and Basset Hound.

What are the clinical signs of Arthritis?


The clinical symptoms of arthritis can include ongoing symptoms, sporadic flare-ups, and a propensity for developing joint issues early in old age.

The manifestation of the disease—a single joint in a previously traumatized animal, bilaterally symmetrical where it results from a developmental disease—is frequently explained by its secondary origin.

While there are many different indicators of arthritis in pets, some typical ones include:-

  1. limping, stiffness,

  2. trouble sitting or standing up,

  3. unwillingness to move,

  4. loss of muscle mass, and

  5. lethargy.

  6. Due to pain and discomfort, arthritis can also lead to behavioural changes like an increase in aggression or irritability.

  7. Commonly acute on chronic presentation -" acute flare".

  8. Apparent sudden onset lameness - investigation in single or multiple limbs.

  9. Soft tissue co-morbidities are sometimes the source of “acute flare”.

How does arthritis develop in pets (Pathophysiology)?


Osteoarthritis, often known as arthritis, is a degenerative disorder of the synovial joints that is defined by a number of pathological processes that result in inflammation, pain, and structural and functional changes to the whole joint. It is the main contributor to chronic pain and is now labeled as a welfare problem.

According to Marte-Pelletier (1998), osteoarthritis is characterized by articular cartilage deterioration, which leads to fibrillation, fissures, severe ulceration, and ultimately tissue destruction and loss. The clinician frequently notices the thickening of the joint capsule in radiographs (X-Rays) and the development of peri-articular osteophytes during the course of the medium and long term.

For cartilage to be able to resist compression, proteoglycan molecules found inside the collagen framework of the cartilage matrix are essential. The cartilage matrix holds water because proteoglycan molecules have a significant affinity for water, which gives the tissue its resilience to compression. Osteoarthritis frequently results in the loss of proteoglycan molecules, which weakens the cartilage's capacity to function mechanically.

Pathophysiological Classification of Arthritis
Pathophysiological Classification of Arthritis

How chronic arthritis develops
How chronic arthritis develops

Even though osteoarthritis is a degenerative condition, most of the changes are a result of ongoing inflammation in the joint. The loss of proteoglycans is mediated by enzymes produced by the chondrocytes, and the release of these enzymes in excessively high levels is correlated with the presence of inflammatory mediators including prostaglandins, nitric oxide (NO), and cytokines like interleukin 1 (IL1).

The Pathways of how chronic arthritis develops
The Pathways of how chronic arthritis develops

How is Arthritis (Osteoarthritis) Classified?


Arthritis or osteoarthritis is classified into three:-

1. Primary Osteoarthritis

Primary OA can be idiopathic, localized or generalized.

Local Osteoarthritis:

This occurs in specific areas especially the knee, hip, spine, or paws.

Generalized Osteoarthritis:

This type occurs mainly in large joints and spine, small peripheral joints and spine,

or mixed areas and spine.

2. Secondary Osteoarthritis

The most common type of arthritis is secondary osteoarthritis, which is normally related to a primary congenital or developmental joint condition in dogs, such as hip dysplasia, but arthritis can also develop secondary to infectious conditions (viral Arthritis, bacterial Arthritis, fungal Arthritis or rickettsial Arthritis). OA can also be post-traumatic, due to calcium deposition disease, inflammatory disease or avascular necrosis.

3. Immune-mediated Osteoarthritis

In dogs, immune-mediated arthritis is uncommon and is linked to systemic disorders with an inflammatory aetiology. They are frequently connected to a polyarthritic patient who is experiencing a variety of non-specific medical symptoms, such as dullness and inappetence, in addition to the effects of their defective joints on locomotion.

As a result, once identified, a generic mechanism for diagnosis can be used, with an emphasis on routine haematology and biochemistry, accurate radiography, and synovial fluid analysis. Fortunately, these patients tend to stand out from the more common osteoarthritics in terms of their presentation and history. It is advisable to use synovial fluid culture and sensitivity rather than relying on precise assays like the often-misleading rheumatoid factor.

Radiographic Classification of Osteoarthritis

Depending on which joint is being examined using medical imaging and specifically characterized by the degree of osteoarthritis, different radiographic techniques are used to categorize osteoarthritis. The choice of treatment for osteoarthritis is based on pain and impaired function, but radiography might be useful before surgery to prepare for the procedure.

Vertebral column

The Kellgren grading is the recommended one for the grading of cervical disc degeneration out of the many grading methods for the degeneration of intervertebral discs and facet joints in the cervical and lumbar vertebrae.

Kellgren grading of cervical disc degeneration

Grade I Minimal anterior osteophytosis
Grade II Definite anterior osteophytosis
Possible disc space narrowing
Some endplate sclerosis
Grade III Moderate disc space narrowing
Definite endplate sclerosis
Grade IV Severe disc space narrowing
Endplate sclerosis
Multiple large osteophytes.
X-ray showing normal cervical bones in a dog
X-ray showing normal cervical bones in a dog


The Samilson–Prieto classification is preferable for the grading of the glenohumeral (shoulder) joint osteoarthritis.

Samilson–Prieto classification

Mild Exostosis of the inferior humerus/glenoid measuring less than 3mm
Moderate Exostosis of the inferior humerus and/or glenoid measuring 3–7 mm, and
of the joint slight irregularity
Severe Exostosis of the inferior humerus and/or glenoid measuring more than 7
mm in height as well as sclerosis and narrowing of the joint space (normal
joint space is 4–5 mm).

X-ray of the stretched foreleg of a dog with ribs, shoulder scapula, upper arm humerus, elbow and forearm radius and ulna.
X-ray of the stretched foreleg of a dog showing the shoulder joint (normal shoulder scapula, and upper arm humerus).


The Kellgren-Lawrence system, sometimes known as the KL system, is the most frequently used radiographic classification method for osteoarthritis of the hip joint. It uses standard radiography.

Kellgren–Lawrence system

0 No radiographic features of osteoarthritis
1 Possible joint space narrowing (normal joint space is at least 2 mm at
the superior acetabulum) and osteophyte formation
2 Definite osteophyte formation with possible joint space narrowing
3 Multiple osteophytes, definite joint space narrowing, sclerosis and
possible bony deformity
4 Large osteophytes, marked joint space narrowing, severe sclerosis
and definite bony deformity

X-ray showing the normal hip of a dog.
X-ray showing the normal hip of a dog.

Osteoarthritis of the hip joint may also be graded by the Tönnis classification. There is no consensus on whether it is more or less reliable than the Kellgren-Lawrence system.

Tönnis classification

Grade Description
0 No osteoarthritis signs
1 Mild: increased osteosclerosis
minor joint space narrowing (normal joint space is at least 2 mm at
the superior acetabulum).
no or minor loss of head sphericity
2 Moderate: small bone cyst
moderate joint space narrowing
moderate loss of head sphericity
3 Severe: large bone cysts
severe joint space narrowing, or joint space obliteration
severe deformity of the head


The International Knee Documentation Committee (IKDC) approach is thought to have the best interobserver precision and correlation to knee arthroscopic findings for grading osteoarthritis in the knee. The Ahlbäck classification and the Merchant system are two further classification schemes for the knee joint.

International Knee Documentation Committee (IKDC) system

Grade Findings
A No joint space narrowing, defined in this system as at least 4 mm
joint space

B At least 4 mm joint space, but small osteophytes, slight sclerosis, or
femoral condyle flattening

C 2–4 mm joint space

D < 2 mm joint space

Osteoarthritis is deemed present at grade B although of minimal severity

How is Arthritis Managed and Treated?


The clinical treatment strategy is focused on maintaining joint function because it is known that the degeneration is unlikely to be reversed and that the processes are localized to the joint. In practice, this means encouraging proper exercise to maintain a healthy lifestyle without further harming the joint.

An appropriate treatment plan to manage the condition and improve the pet's quality of life is usually developed. Pets with arthritis are often treated with a regimen of medicine, diet (weight management), and exercise. Nonsteroidal anti-inflammatory drugs (NSAIDs) are frequently given to treat pain and inflammation, while glucosamine and chondroitin supplements may enhance joint health. The maintenance of joint flexibility and the alleviation of pain can also be achieved through physical therapy and low-impact exercises like swimming or gentle strolls. In immune-mediated osteoarthrtics, these animals require a package of care, focused around controlling their disease with steroids or cytotoxic drugs, but also employing elements of analgesia and physical therapy to minimize the effects of the disease where possible.

Given the complexity of the condition, it is obvious that coordinating a number of factors and adapting them as the disease progresses over the course of the patient's lifespan is necessary for effective therapy. The combination of weight management and physical activity management, which reduces the strain on the joint and increases range of motion and muscular fitness in the surrounding muscles, is without a doubt the most crucial therapy for such patients to reduce joint deterioration while moving. Controlled activity promotes both joint function and maintaining the functionality of other structures in the limb.

How is Arthritis Prevented?


There are a number of actions pet owners may take to lower the likelihood that their animals will acquire arthritis or to decrease the condition's course, but arthritis cannot be completely prevented. Listed below are a few strategies to stop pet arthritis:

  1. Maintain a healthy weight

  2. Provide proper nutrition that is balanced and rich in vitamins and minerals that help keep their joints healthy and reduce the risk of arthritis.

  3. Provide regular exercise to maintain healthy muscles and joints, and also help your pet maintain a healthy weight.

  4. Prevent joint injuries by keeping your pet away from hazards that could cause bone injuries, and use caution when exercising or playing with your pet.

  5. Provide appropriate bedding with a comfortable, supportive bed to prevent joint pain and discomfort.

  6. It is important to consider both the breed and the breeder before making a decision to purchase a pet if arthritis is a concern. Here are some factors to consider:

    1. Breed: There are some dog breeds that are more prone to arthritis than others. Breeds with short legs, like Dachshunds and Basset Hounds, as well as large breeds like Great Danes, Labrador Retrievers, and German Shepherds, are particularly prone to arthritis.

    2. Breeder: Making sure your pet is healthy and free of genetic disorders that can cause arthritis requires choosing a reputable breeder. You should seek out a breeder that is knowledgeable about their particular breed and who tests the health of the breeding dogs to make sure they are not passing on any genetic diseases. Request to see the breeding dogs' and their offspring's health records.

    3. Health history: For a thorough health history of the pet you are interested in, ask the breeder. Included here should be details on the pet's parents, siblings, and any earlier generations. Check the pet's family history for any cases of arthritis or joint issues.

    4. Evaluation: It's a good idea to have a pet examined by a veterinarian before purchasing. Any joint issues or conditions that can raise the likelihood of getting arthritis might be identified by doing this.



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