I've been using the ZeroTension Mouse for quite some time, and while it has all but eliminated my ulnar nerve strain and the pain in my wrist and elbow (by allowing me to rotate my hand to a vertical position where it should be, vs. flat like most mice require), the sheer size of the device forces me to hold my arm too far out to the side of my keyboard, and thus the pain in my shoulder has increased.
I've finally decided to give a trackball a shot.
So far, I love it. I went with the Logitech TrackMan Wheel (corded... the cordless version seemed a waste, and the wireless dongle that plugs into your computer is huge). You have to clean the ball bearings that "float" the track ball every week or so (extremely easy), but the precision is great (though I still use a tablet for drawing and extreme precision), and I love not having to move the device around (it's stationary and the ball moves).
It took about an hour to get used to (I kept trying to move the whole thing [blush]), but now it's fantastic. I love how little desk real estate is quires.
I was also a little worried about pain in my thumb joints from the constant, repetitive motion, but I've been using it for a little over three weeks, and I haven't noticed any pain there at all.
It took me a while to decide between the devices that utilize the thumb and the devices that utilize finger movement. From back in my "regular mouse" days, I remember the excruciating pain in my hand from constantly turning a scroll wheel with my middle finger. I assume the trackballs that utilize finger movement would produce a similar effect, so I went with the thumb ball. Even now, I feel the growing pain from using a scroll wheel with my middle finger again, and I have to be diligent about actually clicking the scroll wheel down like a button to activate using the ball to scroll (I wish I could disable the wheel's ability to scroll, and use it ONLY as a button, but that doesn't seem to be an option).
My one gripe is that the device still positions my hand too flat (thus creating that ulnar nerve strain again). There is some slope to the device, that places your hand a little less flat, but it's still too much.

I tried a couple of different wedges fashioned out of Sculpy, but they were pretty garish. I also tried a giant wad of Silly Putty, and while it's the best thing so far, it tends to flatten out over time. I even thought about cutting off the right edge of the TrackMan Wheel to create a new planar surface (though not enough surface), but I think the best solution is probably going to be creating a wedge out of a block of wood and then maybe trying to integrate it into the side of my keyboard somehow (after I cut the number pad off so my arm isn't stretched out so far).
All of this nonsense could be easily eliminated if Logitech simply built the thing correctly in the first place, with the ball on top and the buttons on the side. Your hand would be in a zero tension position, and all would be right with the world.
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