Post-traumatic injury is a common cause of thumb arthritis. You may be able to remember some past event when you injured that thumb. But an injury isn’t needed to develop OA of the CMC. One in every three women is affected by this problem after menopause.
You may want to see an orthopedic surgeon for a definite diagnosis. An X-ray may help identify what’s going on in the thumb. Treatment for arthritis of this joint early on can prevent worsening of the symptoms.