The cause of osteoarthritis is not fully known. One theory is that some people are genetically predisposed to developing the disease, but this has not yet been proven.

Factors that may contribute to the development of osteoarthritis include:

• obesity, which puts added strain on joints,
• jobs, or activities, that involve repetitive movements of a particular joint, or
• previous damage to the joint, such as from a sports injury.

Rheumatoid arthritis is caused by a fault in the immune system that makes the body to attack its own tissues. This may be inherited genetically (passed on from a family member).