What is it?
In a normal joint, cartilage covers the ends of the bones and allows them to move smoothly and painlessly against one another. In osteoarthritis (or degenerative
arthritis), the cartilage layer wears out, resulting in direct contact between the bones. In the hand, the second most common joint to develop osteoarthritis is the
joint at the base of the thumb. The thumb basal joint, also known as the carpometacarpal (CMC) joint, is a specialized saddle-shaped joint that is formed by a
small wrist bone (trapezium) and the first of the three bones in the thumb (metacarpal). The specialized shape of this joint allows the thumb its wide range of
movement—up and down, across the palm, and the ability to pinch with the fingers (see Figure 1).
Who gets it?
Arthritis at the base of the thumb is more common in women and usually starts after age 40. The cause of this form of arthritis is unknown in most cases. Past
injuries to the joint, such as fractures or severe sprains, and generalized joint laxity may increase the chances of developing this form of arthritis at a younger age.
What are the symptoms and signs?
The most common symptom of thumb basal joint arthritis is a deep, aching pain at the base of the thumb. The pain is often worsened with activities that involve
pinch, including opening jars, turning door knobs or keys, and writing. As the disease progresses, patients may experience pain at rest and at night, and
patients often note loss of pinch and grip strength. In severe cases, progressive destruction and mal-alignment of the joint occurs and a “bump” develops at
the base of the thumb, which is caused by the thumb metacarpal moving out of position in relation to the trapezium. At this point, thumb motion becomes
limited and the space between the thumb and index finger narrows, making pinch activities difficult (see Figure 2). The next joint up may hyper-extend to
How is the diagnosis made?
The appearance of the thumb and the location of the pain are usually very helpful in identifying this