Most types of arthritis are caused by the breakdown of cartilage and synovium (a pocket of fluid between cartilage) within joints. Rheumatoid arthritis and juvenile rheumatoid arthritis are both caused when the body's immune system attacks the tissues that line the joints, which can destroy the joint's cartilage and bone over time. Osteoarthritis is caused by wear and tear of joints, or excessive stress or injury to joints. Post-traumatic arthritis is caused by sudden trauma to a joint, usually as a result of an accident or injury.
Risk factors for arthritis can vary depending on the type, but in general, certain things may increase your risk. Genetics may play a role in the development of certain types of arthritis, so if your family members have arthritis, you're more likely to develop it. Women are more likely than men to develop many types of arthritis. Also, any kind of excessive stress or injury to the joints may increase the risk of developing arthritis, so people who are overweight or who play sports are often at a higher risk. Age also plays a role in the development of some types of arthritis, so being over the age of 40 may increase your risk.
Most arthritis is caused by use and the slow gradual compromise of the joint tissues due to chronic inflammation. This type of arthritis is termed osteoarthritis and generally occurs at an older age. There are other causes of arthirits including autoimmune arthritis like rheumatoid arthritis, septic arthrits from infections, and gout arthritis to name a few that can happen earlier in a patient's life.
The causes of arthritis are not clear, but your genes may be a factor. A healthy weight and exercise can help minimize arthritis pain.
The causes of primary arthritis are not as well understood. In contrast to secondary arthritis, primary arthritis occurs without any directly identifiable cause. Primary arthritis tends to occur after the age of 45, and it becomes more common with advancing age. Arthritis tends to run in families, and most experts believe that it may have a genetic component. It seems reasonable that primary arthritis results from some combination of repetitive microtrauma to the joint, impaired or suboptimal biomechanics, and other unidentified factors, such as a potential genetic predisposition or environmental factors.

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The Arthritis Handbook: Improve Your Health and Manage the Pain of Osteoarthritis (A DiaMedica Guide to Optimum Wellness)
Degenerative or osteoarthritis of the hip, which is the most common form, is usually caused by wear and tear from overuse or trauma to the hip joint.
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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.