Osteoarthritis

A combination of cartilage support and pain management can help reduce joint pain and get your dog active again.

Osteoarthritis is one of the most common ailments in ageing domestic animals. The term refers to a progressive degenerative condition with slow erosion of joint cartilage. In later stages, the surrounding bone reacts to the erosion by producing excessive bone growth, further restricting joint movement and function.

Causes

Osteoarthritis often occurs without an obvious cause, but is more common with age. It is due ultimately to the limited ability of cartilage to regenerate and maintain itself in the face of the cumulative effects of ageing, wear and tear (which is more severe with increased weight), and genetic predisposition (for example, hip dysplasia in dogs).

Sometimes degeneration can be due to an accident which has damaged a previously normal joint.

Signs

Often, the earliest sign of a potential problem is a reluctance to perform certain tasks or specific movements that were previously completed with ease. Initially, a dog owner may notice their dog doesn’t keep up when going for a walk or gets up more carefully after lying down, shifting its weight from leg to leg while rising.

With further joint damage, increased lameness and stiffness may be present for several days following periods of sustained activity or overexertion. As the degenerative changes in joints become more severe, stiffness becomes more apparent after rest periods (such as when an old dog is reluctant to move for a while on waking up). Pets often ‘warm’ out of this stiffness, but cold, damp weather almost always aggravates it.

In later stages, stiffness, lameness and pain are fairly constant and can cause abnormal behaviour. Dogs will often be irritable and reclusive, and may snap when touched or approached. Often, normal behaviour returns when pain is controlled.

The science of osteoarthritis

The body’s reaction to joint injury or strain is inflammation. Unfortunately, the inflammatory process itself can have damaging effects. Inflammatory cells, the body’s defender cells, contain chemicals which kill bacteria, but they can also break down the body’s own cells. The release of inflammatory cells inside a joint results in damage to the components of the joints.

Inside a healthy joint, the bone ends are covered by articular cartilage, which is bathed in viscous joint fluid. This articular cartilage provides a smooth surface to allow for frictionless gliding of the bone ends over each other.

The cartilage is very resilient and acts like the sole of a running shoe, being able to compress and spring back with each step. A tight, mesh network of long-chain molecules called proteoglycans, one of which is chondroitin sulfate, creates this resilience. The viscosity of the joint fluid makes it an effective shock absorber and lubricant; this is due to the presence of hyaluronic acid, another long-chain proteoglycan molecule.

When inflammation of the joint occurs, inflammatory cells enter the joint and release enzymes that break down proteoglycans. That is, both the hyaluronic acid in the joint fluid and chondroitin in the cartilage are damaged.

The loss of hyaluronic acid causes the joint fluid to become thin and watery, so that it can no longer function as a lubricant. Loss of chondroitin from cartilage causes the tightly meshed network to break down, and the cartilage swells and loses its resilience.

With the loss of these two proteoglycans, the joint can no longer function properly and normal exercise causes further joint damage.

Treatment

Any treatment of osteoarthritis has two main aims, reduction of pain and returning the joint, as much as possible, to normal function.

Some things that owners can do to assist osteoarthritic dogs include:

• Reducing the dog’s weight. Increased weight puts more pressure on the joints and increases damage.
• Walking the dog. This keeps joints active and muscles toned. Swimming is also good and is not weight-bearing, so will minimise further damage.
• Avoiding overactivity, including twisting (eg chasing a frisbee or ball) jumping, running and rough play; it will invariably be followed by increased pain.

Medications

Anti-inflammatory drugs

Products that reduce inflammation play a vital role in controlling the pain of osteoarthritis. Care must be taken when using these drugs, as overuse can cause damage to other organs.

They are also useful for those bad days which can often follow a day of overactivity, and to help in the initial stage of treatment while waiting for other measures to become effective.

Chondroprotective drugs

To be considered chondroprotective (or ‘cartilage protecting’) agents, drugs must both stimulate cartilage repair and inhibit ongoing cartilage degeneration. Use of these drugs aims to restore the joint cartilage, fluid and associated tissues to as close to normal as possible.

Chondroprotective agents should not totally replace traditional anti-inflammatory agents, but can be incorporated into preventative or therapeutic treatments to improve healing response and reduce the pain and discomfort caused by osteoarthritis.

There are a number of different cartilage protecting drugs available, including pentosan polysulfate (which is available from vets as Pentosan 100 or Cartrophen Injection) or the oral supplements glucosamine and chondroitin.

Manganese and Vitamin C

Manganese is an essential co-factor in the manufacture of glycosaminoglycans, which, along with protein, create proteoglycans. Vitamin C is essential for the synthesis of collagen (which makes up two-thirds of an adult’s articular cartilage) and is also an anti-oxidant. Both are essential for the production of normal cartilage. Deficiency in either will inhibit cartilage production or repair.

Article courtesy of Dr Finola McConaghy, Technical Services Manager, Nature Vet. Visit: www.naturevet.com.au

Thanks also to Dr Grant Poolman of Bowral Veterinary Hospital for assistance with this article. Visit: www.bowralvethospital.com.au