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Arthritis of the thumb affects the carpometacarpal (CMC) joint most often. This is the joint at the base of your thumb. It allows a great deal of thumb motion in all directions. Pinching and gripping would not be possible without this joint.
Women are affected almost twice as often as men by CMC osteoarthritis (OA). There may be several reasons for this difference between the sexes. First, women have more joint laxity or looseness at this site. Hormones such as prolactin, relaxin, and estrogen are the most likely cause.
Second, there are subtle differences in the anatomy between men and women. The size and shape of the trapezium bone is different in women. The joint surface is smaller and flatter in women. The joint surfaces don't always match up in women as well as they do in men. These differences seem to predispose the joint to early degenerative changes.
Female gender combined with other risk factors may contribute to a higher rate of CMC arthritis among women. For example, trauma resulting in ligament damage and instability may lead to joint changes that increase the risk of joint arthritis.
Not all the reasons for these differences are known yet. More research is needed to help identify risk factors and possibly find ways to prevent this disabling condition for everyone.
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