Dorsiflexion of the wrist is of of the classic causes of computer related RSI. If you rest the heel of your palm on the desk and raise your fingers to use the mouse or keyboard you are exposing your wrist to dorsiflexion, straining the wrist muscles and tendons and running the risk of developing RSI!
Ensure you use correct typing / mouse posture and this risk will be minimized.
I use a simple mouse mat with a built in gel wrist rest/guard. This works for me and prevents dorsiflexion of the wrist.
If using a computer mouse is causing problems why not check out one of the many alternatives or use the mouse less