themadpatter, are you a right-handed cutter? If so, there is a lot of pressure on the left ring and little finger holding the ruler in place. Do you have something on your ruler to make it non-slip (I use the Guidelines 4 Quilting gripper strips)? If you non-slip your rulers, you will not have to press so hard to keep them in place.
I have damaged joints from RA and can no longer use a regular rotary cutter because of the pressure it puts on the right index finger. The Martelli cutter is much less stressful on the hands.