I developed RSI (Repetitive Strain Injury) in my index fingers due excessive mouse clicking. I might consider a trackball as many people suggested.

But how does trackball help? I can see it get 2 buttons and a ball which require some fingers to operate on. Will I RSI while I click on the buttons with other healthy fingers?

Logitech TrackMan Wheel:

I highly doubt this trackball, I assume we are still using the index and middle finger for clicking.

Logitech Marble Mouse:

I think we will use the thumb to click the left button, will I develop RSI on my thumb? And the right button, which finger should I use?

If you know other trackball which might help, please tell me which is the design that help to avoid the stress.