What is it?
The joint at the base of the thumb which allows for the swivel and pivoting motions of the thumb is referred to as the basal joint or thumb CMC (carpometacarpal) joint. Because of its design, it tends to wear out and develop arthritis early in life. Basal joint arthritis is also common in people who have osteoarthritis.
It causes pain at the base of the thumb, particularly during pinching or gripping. It also results in weakness of pinch. 
What caused it?
  • This joint appears to be particularly prone to wear and tear from normal use of the hand. Many people appear to be predisposed to arthritis in this joint, with or without arthritis in their other joints. 
What can you do to help?
  • Ice for five to fifteen minutes at a time on the area which is most swollen and tender. 
  • "Over the counter" non-steroidal anti inflammatory medication (NSAID), such as aspirin, ibuprofen, naprosyn, or ketoprofen. Check with your pharmacist regarding possible side effects and drug interactions.
  • A splint or brace which supports both the wrist and the thumb. A wrist support splint which doesn't support the thumb is not as effective as one that does.
  • Wait and watch.
What can a therapist do to help?
  • Provide a variety of hand splints to support the thumb and the wrist.
  • Help identify aggravating activities and suggest alternative postures.
  • Massage, heat, ice and other treatments aimed at making the area more comfortable.
What can a doctor do to help?
  • Confirm that this actually is the problem.
  • Prescribe stronger NSAID medication or cortisone type medication.
  • Prescribe hand therapy and/or a custom prescription splint.
  • Give a cortisone shot into the joint.
  • Perform surgery to reconstruct the joint. 
There are many different operations that may be done for this condition, but a common approach is perform a total joint reconstruction, which involves three main steps. 

First, the trapezium bone at the base of the thumb is removed. This bone has joint connections to three other bones - and any of these may develop arthritis.

The second step in the surgery involves making a connection between the adjacent sides of the base of the thumb and index finger - to maintain the thumb position. This connection is usually made with a tendon graft and can be done in several different ways. 

The third step is to make a cushion to pad the space between the bones where the trapezium bone used to be. This cushion is usually also made from a tendon graft so that the base of the thumb rests on a pillow of your own body tissue, rather than on the rough surface of an arthritic bone. 

Some surgeons then hold the bones in place with a temporary steel pin.

Recovery takes about three months. Therapy recommendations vary,  but a rough guide is - splint continuously except for bathing 4 to 6 weeks, then progressive mobilization and strengthening exercises for another 4 to 6 weeks to recover of strength and dexterity. Most, but not all patients do this second phase supervised in therapy. Anticipate no two handed sports or heavy two handed lifting for 10 - 12 weeks after surgery. Most strength recovery occurs in the first few months, but can continue to improve for a year or more. 
How successful is treatment?
  • Many people with mild symptoms will improve with a limited period of anti-inflammatory medication and avoiding painful activities.
  • A cortisone shot into the sore area helps most people - at least temporarily. When temporary, relief usually lasts about two months. One or two shots provide permanent relief for less than half of people with this problem.
  • Surgery helps over four out of five people with this problem, but as many as one out of five will have a new problem after surgery, such as numbness on the back of the hand or tenderness of the scar. Surgery is generally helpful in relieving pain, but two problems are not usually improved following surgery:
    • When the problem has caused the thumb to draw into the palm (thumb adduction contracture), surgery does not usually bring it back out, especially if the next joint further out on the thumb has stretched out and bent backward (thumb carpometacarpal hyperextension deformity)
    • Pinch strength may not improve adequately, although pain associated with pinch usually does.
    • The appearance of the base of the thumb may change with surgery.
What happens if you have no treatment?
  • It depends on how much it is bothering you - it really is a quality of life issue. This is not a problem which can spread to other parts of your body. Many people have thumb pain which subsides after a few years, when the arthritis and irritation in this joint "burns out".
  • However, there probably is a limited period of time during which surgery can give the best result. After a period of years, the thumb weakness and the loss of motion of the thumb may not be reversible even with surgery.
  • The main reason to do surgery is to relieve pain and, when possible, prevent the progressive weakness and deformity which may occur. Some people will have a mild problem which flares up from time to time, and treat it themselves or ignore it, others will have a severe problem which prevents them from doing many things with their hand, and feel that they have no choice but to have surgery.
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