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Osteoarthritis

What Is Osteoarthritis?

Last modified: 
30/05/2013 - 12:24

Contributing Author: Guy Slowik FRCS

The word arthritis literally means "joint inflammation" - that is, a joint that is painful, warm to the touch, possibly red, swollen, and associated with a loss of function. "Osteo" is Greek for "bone".

Arthritis is not a single ailment. In fact, more than 100 different conditions can affect the joints and their adjacent bones, muscles, and tissues. They are classified into various major types of arthritis, depending on whether or not inflammation, infection or bleeding is the major component. All of these types of arthritis are completely different, with different presentations, symptoms and treatment.

Osteoarthritis (OA) is the most common form of arthritis.

It is a 'non-inflammatory' type of arthritis, which means that inflammation is not the key component. It is completely different from the less commonrheumatoid arthritis, which is an inflammatory arthritis in which the body's immune system attacks its own tissues, causing joint damage.

  • The causes and treatments of these other arthritis-related diseases differ from OA.
  • While OA sometimes may be painful, it is not always disabling, and unlike rheumatoid arthritis, is unlikely to produce severe deformity of the joints.
  • Osteoarthritis can involve a number of joints, but it is not a disease that spreads to involve other tissues or joints throughout the body.

Osteoarthritis (OA) has been called a "degenerative" condition because it is caused, in part, by wear-and-tear of a joint over time. Its impact is significant:

  • OA occurs in both men and women and usually develops after age 45.
  • More than 16 million Americans, including over 50 percent of people over 65, have some degree of osteoarthritis.
  • Older people often don't realize that they have OA if they are free of pain and other symptoms. However, x-rays often reveal some OA of the spine or fingers in elderly individuals.

Osteoarthritis develops in a joint when cartilage - the smooth shiny tissue that lines and cushions the ends of the bones inside a joint, -begins to break down. This can happen from:

  • Prolonged "wear-and-tear" as we age
  • Prior injury or damage to the joint from trauma or infection
  • Cartilage that is altered by other disease or is genetically weak.

But in most cases we simply don't know what causes it.

Unfortunately, damaged cartilage cannot heal to become normal again, though tremendous research is underway developing methods to restore damaged cartilage.

How It Progresses

Here is how OA progresses:

  • The smooth cartilage that lines and protects the bone ends begins to retain water, and changes occur in some of the chemical substances that make up the cartilage
  • Tiny cracks develop in the cartilage, which then splits further forming clefts and fissures
  • The ends of the bones begin to thicken and grow out from the joint margin. These small bone growths are called osteophytes or "spurs". Actually, these spurs are nature's way of trying to help the damaged joint by allowing the load through the joint to be redistributed. But these bony outgrowths often interfere with the mechanism of joint movement.
  • Cysts, which are small cavities, develop in the bone just beneath the damaged cartilage
  • Fragments of damaged cartilage or bone may break off and float around freely in the joint as 'loose bodies' and may cause additional problems.
  • As the cartilage becomes more damaged, the joint space becomes narrower and narrower.
  • The damage to cartilage within a joint can irritate and inflame the inner lining of the joint called the synovial membrane and cause it to produce excess fluid. It normally produces a lubricant called synovial fluid, which helps to lessen friction in the joint.

    The fluid may then build up within the joint and lead to detectable swelling.

When the cushioning system of the joint is lost, the bones may grind painfully against each other. The joint can begin to stiffen, and movement is impaired.

Some people are fortunate in that despite having these rather severe osteoarthritis changes in a joint, they experience very little, or no pain at all.

Osteoarthritis typically strikes the:

  • Weight-bearing joints (knees, hips, back, feet)
  • Hands
  • Spine

The knee is the most commonly affected joint.

If osteoarthritis develops in the hips or knees, it often occurs in only one joint but may affect any number of joints.

If the hands are affected, a few finger joints may become arthritic at the same time.

  • Bony lumps that arise in the middle finger joints are called Bouchard's nodes.
  • Lumps that arise in the last finger joints are called Heberden's nodes. Heberden's nodes occur most often in women, who are also prone to experience osteoarthritis of the hands in general, as well as the knees.

Nice To Know:

Q: What is the difference between osteoarthritis (OA) and rheumatoid arthritis (RA)?

A: The principle features of the two conditions are not the same, and their treatment is very different. In OA, the cartilage in the joint becomes damaged and, ultimately, the joint degenerates. The joint is not primarily inflamed, although inflammation may occur as a late result.

On the other hand, in RA, there is initial inflammation of the lining of the joint. This produces a soft, tender swelling in contrast to the bony enlargement of OA. Cartilage damage occurs later as a result of this inflammation. The pain of OA is often least troublesome in the morning but may gradually worsen during the day. With RA, the pain and stiffness usually is worst on waking, but gradually improves during the day.

Rheumatoid arthritis is not just a disease of the joints, it is a systemic disease, meaning it affects the whole body. Abnormalities occur in the blood vessels, circulating cells and proteins, as well as connective tissue. Not surprisingly, RA is associated with more generalized disturbances - such as anemia (low red blood cell count) - which are proportional to the activity of the arthritis. Usually more than one joint is involved in RA, with the hands almost always affected.

Facts About Osteoarthritis

  • Osteoarthritis is an inevitable part of aging and can affect any joint.
  • Osteoarthritis is the oldest discovered health problem having been found in dinosaur joints and Egyptian mummies.
  • Osteoarthritis is the most widespread form of arthritis, affecting about 27 million people throughout the United States.
  • Of the 50 million people in the United States with arthritis, two-thirds are under the age of 65 years, and 300,000 are children.
  • The Arthritis Foundation estimates that some 67 million Americans will have arthritis by the year 2030, as age catches up with the baby boomers.
  • Arthritis causes more people to limit their activities than does heart disease, cancer, or diabetes.
  • Exciting research to replace damaged cartilage shows much promise.
 
 
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From Andrew Maynard - Chair of the University of Michigan Department of Environmental Health Sciences, with help from David Faulkner - 2013 Master of Public Health graduate.