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Causes and Risk Factors

Osteoarthritis, a type of degenerative joint disease, affects as many as 20 million Americans and is the number one cause of disability in the U.S. But what joints does osteoarthritis affect? And how do doctors define the types and stages of the disease?

Joint anatomy
Our bones help us stand up straight and the muscles help the bones to move. Bones connect intersections that are called “the joints”. The largest and most used of these joint include the ankles, knees, shoulders, elbows, wrists, and hips.

Together, cartilage and synovial fluid allow for smooth and painless motion in the joints. Cartilage is a material that prevents bones from rubbing against each other during motion and covers the ends of bones. In other words, healthy cartilage allows bones to glide over each other and helps absorb the shock of movement. Additionally, a small bag called the “synovium” holds fluid between the two pieces of cartilage.

What is osteoarthritis?
Osteoarthritis is the most common form of arthritis and is a joint disease that mostly affects cartilage. Unlike some other forms of arthritis, osteoarthritis affects only joints and not internal organs. Osteoarthritis causes pain, swelling and reduced motion in the joints. This common form of arthritis can occur in any joint, but osteoarthritis usually affects the hands, knees, hips or spine.

During a case of osteoarthritis, the top layer of cartilage breaks down and wears away. As a joint loses cartilage, the bones rub together. Over time, this rubbing can permanently damage the joint. Simultaneously, spurs grow out from the edge of the bone which causes pain and damage, and synovial fluid increases. Bits of bone or cartilage can also break off and float inside the joint space. Over time, the joint may lose its normal shape.

Stages of osteoarthritis
There are several stages of osteoarthritis:

  1. Bits of bone or cartilage float loosely in the joint space.
  2. Cartilage loses elasticity and is more easily damaged by injury or use.
  3. Cartilage breakdown leads to an inflamed joint lining (the synovium). Cytokines (inflammation proteins) and enzymes can damage cartilage further.
  4. Cartilage breakdown causes changes to underlying bone. The bone thickens and cysts may occur under the cartilage. Bony growths (spurs or osteophytes) develop near the end of the bone at the affected joint.

Types of osteoarthritis
Osteoarthritis typically affects only certain joints, such as the hips, hands, knees, low back and neck. However, there are two distinct types of osteoarthritis – primary and secondary.

Primary osteoarthritis - Primary osteoarthritis is associated with aging and is considered to be caused by normal “wear and tear”. There is no apparent cause for this type of osteoarthritis.

Secondary osteoarthritis - Doctors diagnose secondary osteoarthritis if there is an apparent cause for the disease. In other words, cartilage breakdown can be associated to injury, heredity, obesity or something else.

Do doctors know what causes osteoarthritis? Are you at risk of developing this degenerative disease? Click here to learn more about the risk factors and what causes arthritis now.

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