Is there any advice or best practices for the design of a desktop mouse and keyboard interface for people who suffer from arthritis, or has any research been done in this field?
You could also think of alternative interfaces, like gesture recognition as implemented by Leap Motion, Kinect and Qualcomm amongst others.
This type of sensors use infrared light and other frequencies to determine the position of the users hands and the position of their fingers.
Based on the information retrieved by those devices you could define gestures that are easy to perform, without any strenuous finger positions so that the user doesn't have to exert himself.
This combined with a good user interface and maybe even speech recognition (List of Speech Recognition Software) would give you a path completely independet of the current Mouse-Keyboard restriction.
So my sugestion:
Using a roller ball rather than a mouse seems to help people with arthritis.
For research, it might be worth picking up the phone to these people (UK):
Helen Hamlyn Centre for Design
Googling "Assistive Technology" will also find some useful information.
1. Assume everyone has arthritis (because eventually, if we're lucky and we live long enough, we all will).
2. Avoid Fitts' Law violations and make it easy for the user to acquire the target.