According to medical definitions, there are more than 40 conditions that manifest as joint pain. The most likely causes are joint injury, joint strain or sprain, infections, cancer and inflammatory joint disease such as the various types of arthritis. Tendonitis and bursitis can also fit into these categories.

Here, we will concentrate on the inflammatory conditions that cause joint pain, the most common form being the condition we all know as arthritis. The word comes from arthro (joint) and itis (inflammation) and inflammation is defined as the symptoms of heat, pain, redness and swelling. Sound familiar? Arthritis, however, is a much more complex and diverse condition than you might at first imagine.

The big picture

Arthritis in its many forms is Australia’s major cause of disability and chronic pain. It affects 16.7 per cent of Australians (more than 3.4 million people), of which 60.4 per cent are women. Sixty per cent are between the ages of 15 and 64 (ie of working age). Fifty-four per cent of Australians over 75 have arthritis.

According to Access Economics, the overall financial cost of arthritis to Australia per year is enormous. It totalled $11.2 billion (or 5.3 per cent of total national health expenditure) in 2004. This is equivalent to 1.4 per cent of gross domestic product. Each year, arthritis accounts for 8.5 million GP visits, 2.2 million specialist visits and 1.4 million visits to other health practitioners. Including pain and suffering, total costs amounted to $19.25 billion in 2004. By the year 2020, it’s expected that 20 per cent of the population (4.6 million people) will be afflicted.

These costs to the Australian healthcare system are greater than those of diabetes, cancer or asthma. The disability burden is similar to that of dementia and second only to depression. Musculoskeletal disease is the major cause of disability and handicap in Australia, and arthritis is the most common form.

Arthritis is a general term for many conditions, of differing causes, involving inflamed, thickened and/or painful and stiffened joints. There are at least 100 known types of arthritis, but only five of these account for 90 per cent of cases. The main ones are classified generally into three groups:

• Osteoarthritis (OA).
• The systemic inflammatory forms of arthritis such as rheumatoid arthritis (RA), systemic lupus erythematosus (SLE) and fibromyalgia, which frequently has an infective trigger. These are often autoimmune diseases.
• Gout.

Australians even have their own special form of epidemic polyarthritis — Ross River Fever (and Barmah Forest disease) — which is increasing in incidence thanks to global warming. It is spread by a virus transmitted by various mosquitoes.

OSTEOARTHRITIS

Osteoarthritis is the most common type of arthritis and is a localised disease that involves increasing deterioration of the cartilage in the joints caused by injury, repetitive use or general wear and tear. It typically runs in families and is three times more common in women than in men.

The structure of the joint is composed of hyaluronic acid, proteoglycans attached to glycosaminoglycans. In the joints, cells called chondrocytes make and maintain the integrity of the cartilage. These cells receive nutrients from the synovial fluid, which also removes waste byproducts. The synovial activity is triggered by movement, which compresses and releases the sponge-like cartilage.

Osteoarthritis is characterised by the degeneration, destruction and erosion of the cartilage in the joint, with bony outgrowths (Hebderden’s Nodes) often forming at the edges of the joints. The synovial fluid changes and the elasticity of the cartilage degenerates. The joint surfaces become irregular, flattened and poorly adjusted to each other. This causes the joint cavity between adjacent bones to narrow until eventually the cartilage disintegrates and the bones may directly scrape against one another.