Arthritis is a condition that irritates or destroys a joint. Although there are several types of arthritis, the one that most often affects the joint at the base of the thumb (the basal joint) is osteoarthritis (degenerative or "wear-and-tear" arthritis).

Causes
Osteoarthritis occurs when the smooth cartilage that covers the ends of the bones begins to wear away. Cartilage enables the bones to glide easily in the joint; without it, bones rub against each other, causing friction and damage to the bones and the joint.

The joint at the base of the thumb, near the wrist and at the fleshy part of the thumb, enables the thumb to swivel, pivot, and pinch so that you can grip items in your hand. Arthritis of the base of the thumb is more common in women than in men, and usually occurs after age 40. Prior fractures or other injuries to the joint may increase the likelihood of developing this condition.

Symptoms
If you have osteoarthritis of the thumb, you may feel pain with activities that involve gripping or pinching, such as turning a key, opening a door, or snapping your fingers.
There may be swelling and tenderness at the base of the thumb, or an aching discomfort after prolonged use. Loss of strength in gripping or pinching activities, limited motion, an enlarged, "out-of-joint" appearance, and the development of a bony prominence or bump over the joint are also common symptoms.

Treatment
In its early stages, arthritis at the base of the thumb will respond to nonsurgical treatments. These may include icing the joint for 5 to 15 minutes several times a day; taking an anti-inflammatory medication such as aspirin or ibuprofen to help reduce inflammation and swelling; and wearing a supportive splint to limit the movement of the thumb, allowing the joint to rest and heal. The splint may protect both the wrist and the thumb. It may be worn overnight or intermittently during the day. Because arthritis is a progressive, degenerative disease, the condition may worsen over time. The next phase in treatment involves a steroid solution injection into the joint. This will usually provide relief for several months. However, these injections cannot be repeated indefinitely.

When conservative treatment is no longer effective, surgery is an option.