Osteoarthritis of the thumb
The base of your thumb is where the metacarpal bone of the thumb meets the trapezium, a small carpal bone in your wrist. This joint is called the carpometacarpal joint, or CMC for short and it is commonly affected by osteoarthritis.
The CMC joint is very reliant on the ligaments surrounding the thumb joint and on the shape of the bones to stabilise the thumb when you are pinching or grasping around an object. Over time, the stability of the thumb may be affected by changes to the ligaments and bone surfaces, changing the way that the joint moves and causing problems with everyday tasks.