Arthritis of the Base of the Thumb

What is it?

The joint at the base of the thumb is known as the basilar joint (See Figure 1). It is different from other joints in the hand. All of the other joints in the hand are hinges that move in a single plane. The joint at the base of the thumb is a universal joint and moves in all directions (See Figure 1).This makes the basilar joint particularly prone to wearing out. In a normal joint, there is a cartilage layer that covers the end of each bone. Arthritis is a condition where the joint becomes inflamed and the cartilage wears out. In the thumb basal joint (or CMC joint), this is a condition that can occur from normal use and age, trauma, or from repetitive activity. The mechanism involves stretching of the ligaments that stabilize the joint so that the joint becomes unstable. After the joint becomes unstable, a shear force occurs, which can lead to relatively rapid deterioration and wearing out of the cartilage. This causes the bone to rub against each other causing the joints to be inflamed and painful. (See Figures 2 and 3 for images of normal and arthritic distances between the bones).

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 (looseness) 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 pinching, 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. They also feel a grinding, or crepitus, at the base of the thumb. In severe cases, progressive destruction and mal-alignment of the joint occurs and a “bump” develops at the base of the thumb. This is caused by the thumb metacarpal bone moving out of position in relation to the trapezium bone (See Figure 2). At this point, thumb motion becomes limited and the space between the thumb and index finger narrows, making pinch activities difficult. The next joint up (the MP joint) may hyper-extend to compensate for the lack of proper function in the basal joint below.

How is the diagnosis made?

The appearance of the thumb and the location of the pain are usually very helpful in identifying this condition. Applying longitudinal pressure along the thumb and twisting or grinding the basal joint is also helpful in reproducing symptoms. Although x-rays help confirm the diagnosis, symptom severity often does not correlate directly with the joint’s appearance on the x-ray.

What are the treatment options?

In less severe cases, conservative (non-surgical) treatment is often helpful. This consists of splinting, anti-inflammatory medication, and rest. In a limited number of cases, cortisone injections can also be helpful. Splints to stabilize the thumb can generally be provided from our office, but occasionally a patient may need to be sent to a hand therapist to be provided with a customized splint. In cases where there is advanced arthritis and significant pain, conservative treatment is often not helpful. Even some patients with relatively mild arthritis will not get pain relief from non-surgical treatment. In these cases, a variety of surgical techniques are available that can successfully reduce or eliminate pain and improve thumb position and function. Surgical reconstruction involves excision of the trapezium bone and stabilization of the base of the thumb metacarpal bone utilizing a portion of the flexor carpi radialis tendon. The remaining portion of this tendon is used as an interposition to replace the trapezium bone. This procedure is highly successful in giving pain relief and allows for maintenance of good motion of the thumb. In rare cases, patients with high physical demands will require a fusion of the basilar joint. However, in most situations, the tendon interposition described above is the best option. If the next joint in the thumb (the MP joint) is unstable, this joint may need to be stabilized or fused at the same time. The recovery from this surgery takes three months or more. There is generally a month of cast or splint immobilization followed by two months of therapy.The long-term results from this surgery are quite good, with the patients regaining better strength and having good pain relief. While this is an excellent long-term treatment for this condition, it is important to emphasize that there is substantial recovery time and you should discuss this carefully with your doctor before proceeding with the surgery.