Variation is important, using any physical interface repeatedly is going to cause problems. Try moving more between a mouse, trackpad, keyboard and control surface. There is no perfect interface, eventually you strain something if you use a single interface too often.

I recently bought a kensington expert mouse which has definitely reduced the pain I had. Larger hand / finger movements involved in using the trackball help prevent repetitive strains apparently. However, the more I use it the more I can feel tension building up in other parts of my hand and arm, but not as bad as it was. I think Iain is correct in saying that variation is key.

Also, a good chair will help back and shoulder pains a lot.

There's a series of mice made by Evoluent, I saw someone using one of them the other day and it looks pretty crazy. It's basically a mouse, but it's designed so you hold it 'vertically'.

Rather than me try to explain it badly, here's a link to the site: click here

The little blurb at the bottom seems to confirm better health benefits as well!

Cheers

Sorry you're suffering with this, I've been there in a major way. It's important to address dekstop ergonomics, and as you have found, it's largely a trial and error process to find a good fit for yourself.

Of equal importance though, is to take the rest of your body into account as well. Your body is a single machine, with all of its parts acting as a team. My first recommendation is that you try to work standing up. It might sound weird, but it can really do wonders. Thing is, sitting in a chair for any extended period of time is one of the worst things you can do to your body, no matter how mundane it may seem. It pretty much goes against everything that your body is designed to do.

I had every back, arm, hand and neck issue you could imagine. I tried every mouse, pen and pointer in the book. Tried numerous chairs, balls, benches etc. Only when I switched to working standing up did everything dramatically improve. And I mean dramatically. At first you'll get sore feet, some lower back aches etc, that's from the sheer weakness that has developed from years of sitting. Once you get over that short hump it becomes awesome, and I'd never go back.

Not only is it better for your spine, legs, core/abs, neck, hands, etc - it's also a major productivity enhancer. You are just way more alert and "with it" when standing up. Your brain equates sitting with rest naturally. Extra bonus: You burn an extra 300-400 calories per day by simply not sitting on your butt.

This isn't an input device recommendation, but I felt it worth mentioning as I dealt with the same issues for a long, long time.

My vote goes to trackballs. I only use trackballs in my studio, and hasn't got any problem with my elbows or shoulders in years. What causes such problems is the fact that neighter elbow-joints or shoulders are made for fine motorical movements like the hand and wrist is. It may take some time to get used to a trackball, frankly I mostly have to re-learn the alignment of the controller every time I get a new one, but all in all it actually speeds up my work something tremendously after the few days/about a week it takes to get used to the new controller :-)

At home I have a regular mouse due to the fact that good trackballs are quite costly, but there I take support by the table with the lowest part of my hand, the ball-bone at the lowest of the hand (the same bone-part used in Karate for breaking stuff with hand-tameshiwara, actually!), and only move the mouse with the fingers in movements no bigger than I can make them without actually moving the elbow at all. It's not easy to explain, in short I move the hand and fingers with the hand never leaving the table at all, but never the elbow or anything above the wrist. For it to work the mouse musn't be too big as you have to be able to cover it completely with your hand,