Arthritis is inflammation of one or more joints, which results in pain, swelling, stiffness, and limited movement. There are over 100 different types of arthritis.

See also: Joint pain

Arthritis involves the breakdown of cartilage. Cartilage normally protects the joint, allowing for smooth movement. Cartilage also absorbs shock when pressure is placed on the joint, like when you walk. Without the usual amount of cartilage, the bones rub together, causing pain, swelling (inflammation), and stiffness.

You may have joint inflammation for a variety of reasons, including:

• Broken bone
• Infection (usually caused by bacteria or viruses)
• An autoimmune disease (the body attacks itself because the immune system believes a body part is foreign)
• General "wear and tear" on joints

Often, the inflammation goes away after the injury has healed, the disease is treated, or the infection has been cleared.

With some injuries and diseases, the inflammation does not go away or destruction results in long-term pain and deformity. When this happens, you have chronic arthritis. Osteoarthritis is the most common type and is more likely to occur as you age. You may feel it in any of your joints, but most commonly in your hips, knees or fingers. Risk factors for osteoarthritis include:

• Being overweight
• Previously injuring the affected joint
• Using the affected joint in a repetitive action that puts stress on the joint (baseball players, ballet dancers, and construction workers are all at risk)

Arthritis can occur in men and women of all ages. About 37 million people in America have arthritis of some kind, which is almost 1 out of every 7 people.

Other types or cause of arthritis include:

• Rheumatoid arthritis (in adults)
• Juvenile rheumatoid arthritis (in children)
• Systemic lupus erythematosus (SLE)
• Gout
• Scleroderma
• Psoriatic arthritis
• Ankylosing spondylitis
• Reiter's syndrome (reactive arthritis)
• Adult Still's disease
• Viral arthritis
• Gonococcal arthritis
• Other bacterial infections (non-gonococcal bacterial arthritis )
• Tertiary Lyme disease (the late stage)
• Tuberculous arthritis
• Fungal infections such as blastomycosis

If you have arthritis, you may experience:

• Joint pain
• Joint swelling
• Stiffness, especially in the morning
• Warmth around a joint
• Redness of the skin around a joint
• Reduced ability to move the joint

First, your doctor will take a detailed medical history to see if arthritis or another musculoskeletal problem is the likely cause of your symptoms.

Next, a thorough physical examination may show that fluid is collecting around the joint. (This is called an "effusion.") The joint may be tender when it is gently pressed, and may be warm and red (especially in infectious arthritis and autoimmune arthritis). It may be painful or difficult to rotate the joints in some directions. This is known as "limited range-of-motion."

In some autoimmune forms of arthritis, the joints may become deformed if the disease is not treated. Such joint deformities are the hallmarks of severe, untreated rheumatoid arthritis.

Tests vary depending on the suspected cause. They often include blood tests and joint x-rays. To check for infection and other causes of arthritis (like gout caused by crystals), joint fluid is removed from the joint with a needle and examined under a microscope. See the specific types of arthritis for further information.