I've been having more and more trouble grasping and pinching small objects with my right hand. It seems like my thumb just doesn't move like it should. And there's a round bump around the base of the thumb like the bone is getting bigger. What could be causing these symptoms?
You may be describing the classic symptoms of osteoarthritis (OA) of the carpometacarpal (CMC) joint of the thumb. This is the most common place in the hand to be affected by arthritis.

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.