A 45-year-old secretary notices the gradual onset of aching at the base of her right thumb, especially hitting the space bar while typing and gripping a pen while writing. 

A 65-year-old grandmother has recently taken up crocheting. She notices a gradual onset of pain in her thumb, which occasionally is so severe that it wakes her up at night. 

These individuals have all developed problems related to the carpometacarpal joint at the base of the thumb. This common disability can be caused by a single traumatic event, by excessive repetitive use, or by initiation of new activity. The treatment depends on which anatomic structures are injured, the extent of that injury and the amount of underlying arthritis present in the joint.

Anatomy
Acute Injury
Chronic Stress
Arthritis
Diagnosis and Treatment
 

Anatomy
The carpometacarpal joint is located at the base of the thumb and serves as an anchor to the hand. It is a rather shallow, saddle-shaped joint which allows a good deal of motion for important activities. However, this freedom of movement comes at a price. 

The joint relies heavily upon adjacent ligaments and tendons to maintain the stability that is so important for gripping and pinching. Damage to these supporting structures may result in an unstable joint, which cannot support such activities. The pain and disability are most noticeable during use. In contrast, damage to the joint surfaces may cause constant pain that worsens with activity, but also occurs at rest. This spectrum of problems can be illustrated with a few specific examples. 

Acute Injury
In younger individuals, such as the softball player, the joint surfaces are usually in good shape. "Jamming" or other injuries to the thumb usually cause ligament damage of varying degrees. If the ligament is bruised but not stretched, a period of immobilization in an appropriate brace will provide relief. If the ligament is stretched or ruptured, a period of casting may be required. In some cases, surgery may be necessary. The treatment required depends on the severity of the ligament injury. 

Chronic Stress
Damage to the ligaments surrounding the base of the thumb does not have to occur all at once. Repetitive use and stress can result in ligament stretching, leading to joint looseness and pain. The case of the secretary who used a keyboard and pen all day is a typical example. As in the first example, the treatment is dictated by the severity of the injury to the ligaments. This can only be determined by careful examination. 

Arthritis
Because the base of the thumb is stressed so much by everyday activity, it is particularly susceptible to the wear and tear arthritis that can occur in any joint. As time passes, this type of arthritis follows a predictable course, beginning with minimal joint involvement and ending in complete joint destruction. Joint inflammation produces a pain, which is made worse by activity, but also occurs at rest, as was the case with the crocheting grandmother. Occasionally, it may go unnoticed until it is triggered by a new activity. The treatment depends on the degree of destruction. If joint involvement is minimal, a program of appropriate splinting, activity modification and arthritis medication may suffice. However, if joint destruction is severe, surgery may be necessary to replace the joint. The best way to determine the health of the joint is through careful physical examination and x-rays. 

Diagnosis and Treatment
Many distinct problems can result in pain in the thumb. A careful examination is necessary in order to differentiate among the various injuries mentioned here, as well as other injuries not mentioned. An appropriate plan for treatment, based upon a thorough understanding of the underlying problem, can then be initiated.