Reviewed by: HU Medical Review Board | Last reviewed: September 2013.

Osteoarthritis is the most common form of arthritis, affecting 26.9 million people in the US and accounting for more disability than any other chronic disease, including heart disease, diabetes, and back or spine problems.1,2


How is osteoarthritis different from RA?

Osteoarthritis differs from RA in some important ways:

  • Difference in symptoms. The most prominent symptoms of RA are inflammation and swelling of joints. However, with osteoarthritis inflammation and swelling occur less commonly.
  • Difference in age of onset. RA usually begins in individuals between the ages of 25 and 50 years, but may also affect children. By contrast, osteoarthritis typically begins after the age of 40 years and almost never affects children.
  • Difference in affected joints. RA affects the majority of joints and particularly the knees, elbows, shoulders, wrists, and fingers. Osteoarthritis typically affects weight-bearing joints, for instance, the hips, knees, ankles, and spine.


Who is at risk for developing osteoarthritis?

Osteoarthritis is a form of arthritis that occurs with advancing age or due to injury or trauma to the joints. When osteoarthritis occurs without an apparent joint injury or trauma or without other explanation, we refer to this as primary osteoarthritis. Osteoarthritis linked to injury or trauma is called secondary osteoarthritis. Many professional athletes who have injuries during their careers typically develop secondary osteoarthritis.

There are some risk factors that increase the likelihood of developing osteoarthritis. These include age over 45 years, a history of joint injury or repeated joint stress, female gender (women are more likely to develop osteoarthritis), having a parent or parents who had osteoarthritis, and being overweight.3


Risk factors for developing osteoarthritis

Age over 45 years
As you age, cartilage and joints structures tend to degrade
Degradation is not inevitable with increased age
Female gender
Women are more likely to develop osteoarthritis, 3 times more likely than men
This may have to do with hormonal differences or the size of joints and related structures
History of joint injury or repeated stress
Accidental injury to your joints, whether sports-related or from a fall, can increase your risk for osteoarthritis
Repeated stress on your joints, such as what a baseball pitcher experiences, can increase the risk for osteoarthritis
Parental history
If your parent or parents had osteoarthritis, you may have the same genetic susceptibility for the disease
One study found that genes accounted for about half of the risk for developing hip osteoarthritis
Carrying excess weight can stress your joints and related structures and increase risk of osteoarthritis


What is the cause of osteoarthritis?

Similar to RA, the exact cause of osteoarthritis is not known. However, there is some consensus that osteoarthritis results from wear and tear on joints and related structures that occurs over time, with a failure of the body to repair this damage. Unlike RA, where inflammation caused by an autoimmune response is the primary driver of the disease, in osteoarthritis, inflammation appears to be secondary to irritation that occurs where the joint has degenerated.

As the body ages, joint cartilage can lose fluid and become brittle. This leads to the formation of cracks and deterioration of the cartilage. Cartilage serves as a kind of shock absorber inside joints, preventing the ends of bones from rubbing against one another, while absorbing impact from movement. With the deterioration of cartilage, bone and joint damage can occur, resulting in the symptoms of osteoarthritis, including pain, stiffness, and loss of movement.

To understand osteoarthritis, it helps to understand the composition of cartilage and how it works. Healthy cartilage is a truly amazing substance that is both slick and tough. It is essential for proper and painless joint function and movement. Cartilage is made up mostly of water (up to 80% of it is water).

The water in cartilage allows it to absorb and cushion the ends of bones and to lubricate the joints. Cartilage is also composed of collagen, a kind of protein that makes up our connective tissues. Collagen has a mesh-like structure. It has an elasticity that helps it absorb shock and impact during movement. On a microscopic level, the mesh-like structure of collagen is occupied by proteoglycans, a kind of protein that can soak up and release water in response to changes in pressure. The proteoglycans within cartilage allow it to mold itself to the space inside the joint and respond to changes in pressure that occur as your joints and bones move. Finally, cartilage contains cells called chondrocytes that are responsible for the repair and maintenance of cartilage. Chondrocytes work to breakdown and dispose of old collagen and proteoglycans and help produce new proteins to carry out the functions of the joints.

We don’t understand exactly why cartilage deteriorates in primary osteoarthritis, but we think that it may be due to a loss of balance between the breakdown and replacement of collagen and proteoglycans. For some reason, chondrocytes may produce too much of the chemicals (enzymes) that breakdown collagen and proteoglycans and not enough of the chemicals that replace these proteins, or the reverse, chondrocytes may overproduce the chemicals that replace collagen and proteoglycans, resulting in flooding of the joint with liquid and a net loss of chondrocytes.


What are the signs and symptoms of osteoarthritis?

Osteoarthritis typically affects the neck, lower back, hips, knees, ends of the fingers, and base of the thumbs. The signs and symptoms of osteoarthritis include:

  • Joint pain, tenderness, and swelling
  • Joint stiffness resulting in loss of movement
  • Warmth around the joint
  • Cracking, popping, or crunching sounds in joints
  • Bony lumps or growths on fingers


How is osteoarthritis treated?

Treatment for osteoarthritis includes both prescription and over-the-counter medications to relieve pain and inflammation. These include acetaminophen (Tylenol, Liquiprin, Datril) for pain relief (these drugs will not provide relief of swelling), and non-steroidal anti-inflammatory drugs (NSAIDs) (aspirin, Advil, Aleve, Motrin) for relief of pain and to reduce swelling.

Management of osteoarthritis should also include exercises to improve flexibility, endurance, and strength. Exercise is an important part of maintaining healthy joint function, so even if you have considerable pain from osteoarthritis, you should engage in some program of exercise. Before you start exercising, consult with your doctor to find out what exercises are appropriate for you.

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