You may not think much about your thumb—after all, it’s a digit and not even a finger—but it plays an important role in your everyday life. You use your thumb to grasp and pinch objects, open jars, play the guitar, dress yourself, operate tools, and perform countless other tasks.
And even if you do appreciate your thumb, you might not be aware of how the first carpometacarpal or “CMC” joint helps it do its job. The CMC joint is located where the thumb (metacarpal) bone meets the wrist (carpal) bone.
As this joint becomes worn, often due to age, it can lead to a painful condition called thumb arthritis (also known as CMC arthritis or basal joint arthritis). Arthritis refers to inflammation in a joint, causing the pain, stiffness, and swelling that makes it so difficult to perform even simple tasks. Thumb arthritis is the second most common type of arthritis in the hand.
Xuan Luo, MD, a Yale Medicine hand, shoulder, and elbow surgeon, draws from evolutionary history when he explains thumb arthritis to patients. “If you look at certain ancestors of ours, not all of them had opposable thumbs [meaning they can be placed opposite the fingers, which is what allows us to grasp objects]. This is a relatively new evolutionary invention,” Dr. Luo says. “And like any new feature on your car or computer, it’s not always tested well and tends to wear out first. As we get older, that CMC joint in particular often wears out, causing pain at the base of the thumb.”
Treatment for thumb arthritis starts conservatively with the patient wearing a soft brace. If that doesn’t work, injections at the base of the palm may work. And if there still isn’t relief, surgery is an option.