Trackball
Does trackball operation involve the thumb? Possible arthritis in thumbs?
It depends on what trackball you buy. I have the Logitech M570 which is operated by the thumb and despite extensive use (several hours every day),
I feel a lot less strain than with a normal mouse and nothing in my thumb. I tried to go back to a normal mouse and I quickly felt it in my wrist.
You can however get many other trackballs that are operated by other digits.