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Factors involved in the development of arthritis.

As mentioned previously, the two major types of arthritis are osteoarthritis (which is more common in animals) and rheumatoid arthritis (which is more common in people).

Osteoarthritis

Osteoarthritis develops because of wear and tear on the joints. The cartilage covering the joints will wear, and be replaced by fibrocartilage (this is the 'scar type' cartilage that is produced in reaction to joint cartilage damage). There may be some bony reaction around the joint, and some joint capsule thickening. This may or may not be apparent in the gait of the animal, i.e. stiffness, lameness etc.

There are several factors that contribute to these changes.

• Age: The longer an animal has been alive, the more use its joints will have had.
• Weight: The heavier an animal, the more stress on the joints. With horses, this may also apply to a heavy rider on too small a horse!
• Activity level: A fitter more active animal may put more stress on its joints. Also, animals that twist and turn a lot, i.e. sudden massive changes in the force directions in the joints, may also increase the risks.
• Genetics: A massive subject, but can broadly be broken down into the following:
• Breed: Some are more prone than others, for example heavier breeds.
• Ancestry: The chances of an animal developing arthritis increase if the parents had it.
• Osteochondrosis (OCD): A subject in itself, but briefly a problem of young dogs, mostly associated with growth and concurrent cartilage development (this is very simplified).
• Hip dysplasia: Another huge subject, briefly poor hip formation: leading to abnormal joint forces; leading to arthritis.
• Conformation: Poor confirmation leads to abnormal forces on the joints.

The list does go on.

• Diet: Obviously this has an influence on the weight, but one should bear in mind that if a young dog is fed 'too quickly', it will grow 'too quickly', leading to joint development problems. Also, the diet should be correctly balanced as far as mineral and vitamin levels go, at all stages of life. For example, too much calcium ("for developing strong teeth and bones"), may be as harmful as too little. People also tend to give cod liver oil on the assumption that this is good for joints - it is in people, but in animals the amount is very often over fed, as it saps vitamin D from the diet (one of the fat soluble vitamins) which is involved in calcium balance in the body.

• Trauma: Any damage to the joint will increase the risk of arthritis. This can range from mild sprains or strains (mild increase in the risk), to joint capsule / ligament damage, to fractures in or around the joint. Also, any surgical joint intervention will also increase the risk of arthritis.

This is by no means an exhaustive list, but probably covers the major factors.

Rheumatoid arthritis

Rheumatoid arthritis is a more complicated disease to understand, but a simpler condition to conceptualise.

It may be considered as an adverse joint reaction to the deposition in the joints of immune mediated particles, either to the joint, or precipitated elsewhere in the body. Sounds complicated, but look at it as an abnormal immune system reaction. This may be triggered by an infection elsewhere in the body, or by an auto immune reaction (i.e. an immune system reaction to one of the body's own components).

Note that osteoarthritis and rheumatoid arthritis can coexist.

Again, this is a vast subject, very closely tied to the subject of immunology, and one which is beyond the scope of these articles.

There are of course many other forms of arthritis, e.g. suppurative arthritis, septic arthritis, systemic lupus erythematosis (which is an auto immune disease), and so on.

Notice:
Chris is not, and does not claim to be, an expert or specialist in the field of arthritis. He is a practising veterinary surgeon with an interest in alternative therapies. These articles are not intended to be definitive discussions on arthritis. While he is pleased to answer any general queries you may have about arthritis and joint diseases, it may be difficult to answer any specific questions about your pet or horse. Remember, the first port of call for assesment and diagnosis of any joint problems should be your own veterinary surgeon.

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