Osteroarthritis: MINI SERIES #1

Osteoarthritis (OA), otherwise known as arthritis, degenerative joint disease (DJD), or osteroarthrosis is a progressive and irreversible degenerative condition of the joints. OA can be seen in most species and increases with age. Even though dogs may never show obvious signs of OA, as many as 60% will have X-ray evidence of it in their lifetime. There radiographic changes can be seen in upwards of 90% of cats over the age of 12 years.

What makes up a healthy joint?

Joints are where 2 or more bones meet and are generally mobile allowing bones to move. A healthy joints is composed of the following:

  1. Cartilage: tissue that covers the surface of the bones in a joint. It’s kind of like a cushion and helps to reduce friction in the joint

  2. Synovial membrane: tissue that surrounds the joint to seal it into a joint capsule

  3. Synovial fluid: clear sticky fluid inside the joint

  4. Meniscus: curved part of the cartilage

  5. Ligaments: surround the joint to limit joint movement by connecting bones together

  6. Tendons: line the sides of joints and attach to muscles to bones to help control the movement within the joint

We need everything that creates a healthy joint to function properly to prevent pain/disease in that joint.

How does OA start?

We can categorize OA into two different types:

  1. Primary arthritis: part of the normal aging process of wear and tear of the joints

  2. Secondary arthritis: results from trauma, joint instability/incongruity, or immobilization of the joint

This starts with a disruption in the normal environment in the joint and damage to the healthy cartilage. Good news! The damaged cartilage releases cells (chondrocytes) that attempt to repair the defects. The problem is, it also induces an inflammatory cascade that stimulates enzymes that degrades the cartilage. Eventually, the repair system can’t keep up with the rate of cartilage degradation. So, the body tries to attempt to stabilize the joint in other ways like laying down abnormal bone growths/spurs and thickening the connective tissue in the joint. This decreases mobility. With the loss of cartilage and decreased mobility in the joint, the synovial fluid becomes thinner; more weight is put on tendons/ligaments which can cause injuries; and surrounding muscles become less supportive resulting in reduced muscle mass.

The process is quite cyclical… there is damage/wear so the joint become inflamed which releases enzymes/cells which causes the joint to be more inflamed which releases more enzymes/cells which damages other structures which causes the joint to be more inflamed and so on…

Risk factors

  • Obesity

  • Joint instability (ligament injuries, trauma, abnormal boney conformation)

  • Joint incongruity (dysplasia, trauma)

  • Overactivity (working dogs, athletic)

What are the clinical signs do pets show?

Dogs and cats actually present quite differently.

In dogs, lameness/limp is usually the very first sign they will show. It might happen only every once in a while, it might get progressively worse over time, or it might be persistent. Often, people I hear clients describe the lameness as “he/she is very stiff after resting but then it seems to get better once he/she starts moving a bit”. It also tends to get worse after periods of overexertion. We may also see signs of stiffness, swelling, or pain in a joint(s).

Cats are a little bit different in that they will often present without an obvious lameness. Instead, they may show signs of inactivity, irritability/aggression, decreased grooming, hiding, difficultly getting in/out of the litter box (defecating/urinating outside the box), etc. We may also see signs of stiffness, swelling, or pain in a joint(s).

Stay tuned for the next mini series that explains diagnosis and treatment options of OA.

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