For most forms of arthritis, the cause is unknown. Infectious forms may be traced to a specific bacterial agent (such as gonorrhea) that invades a joint. Osteoarthritis is the result of the breakdown of cartilage, but it is not fully understood why the degeneration begins. It may be the result of a malfunction in the cartilage and the metabolism of the underlying bone. Rheumatoid arthritis (RA) is an autoimmune condition, and the causes of autoimmune conditions are not well understood.
Elements called risk factors may increase the likelihood of developing a disease or condition. However, not everyone with the disease may exhibit risk factors, and not everyone with risk factors develops the disease. Some of the risk factors associated with forms of arthritis include:
• Age. Osteoarthritis, the most common form of the disease, is more likely to develop as people get older. More than 70 percent of people over age 70 show evidence of osteoarthritis in x-ray images, according to the American College of Rheumatology. However, not all of them exhibit symptoms.
• Weight. Excess weight may increase the likelihood of developing osteoarthritis. The extra stress placed on joints may contribute to the degeneration of cartilage.
• Sex. Women are much more likely than men to develop many types of arthritis, including osteoarthritis and RA. A few arthritic conditions are more common in men, including gout and ankylosing spondylitis, which usually develops in men under age 40.
• Personal medical history, including joint injury. People who have experienced acute joint trauma or overused certain joints in sports or in their work may develop arthritis. An earlier joint injury also makes it more susceptible to developing arthritis.
• Genetics. Studies show that a genetic marker called HLA-B27 can be found in some people with certain forms of arthritis, such as ankylosing spondylitis. Many people with RA have a gene called HLA-DR4. Not every person with arthritis has these genes. People who do have the gene have a greater tendency to develop some forms of the disease. Heredity may play a role in developing other forms of arthritis as well.
• Lifestyle. In addition to obesity, other lifestyle factors may contribute to certain forms of arthritis. For instance, gout may develop when excess uric acid accumulates in the joints. Uric acid comes from food or drink high in purines, so people with excess purines in their diet (e.g., alcohol, organ meats, anchovies) are more likely to develop gout.