This may help someone out there. I had chronic tennis elbow for years, tried a huge array of options to fix it and failed... until: I found a _vertical_ mouse.
Wish there was more competition in ergonomic input devices. Was just searching for a new mouse and couldn't find a vertical mouse with acceptable reviews.
Ended up forgoing the vert. mouse altogether and buying a Logitech MX Master to replace my Logitech G500 (which I've used for many years and is now discontinued) and I'm pretty happy with it so far. I'm even pleased with its gaming performance (probably not OK for highly competitive or pro gamers, but np for me). Mouse was visibly sluggish over Bluetooth but works great over Logitech RF.
Although the MX Master is not billed as an ergonomic device, it fits my hand better than the G500 and I already feel some relief of the slight pain in my right wrist.
I've used a Kinesis Advantage keyboard for about 3 years (and the MS Ergo 4000 for several years before that, in response to pain that developed before I even turned 20) and it's been a godsend. Would like to find a good ergo mouse before I'm forced to.
The DXT Mouse by Kinesis is the absolute best mouse I've ever used. It's ambidextrous so you can switch back and forth to do wear-leveling. It's crazy comfortable. You may have to raise it up on a book or something though next to your keyboard due to the different way you hold it.
I switch back and forth between a DXT mouse and a trackball every couple days so that I'm not always doing the same motions.
I also use auto-click software so that I don't have to click the mouse. I use RSI Guard which has this feature.
The Microsoft Sculpt Ergonomic mouse is semi-vertical (this might depend on how you hold it) and tracks better than the Evoluent mouse I was using before, although the ergonomics are probably not as good. The build quality is also better IMO than the Anker / Sharkk vertical mice popular on Amazon.
Haven't tried the DXT mouse mentioned in the other comment.
Yup, vertical mouse solves most of my right-side issues. It can't be one of those cool-looking vertical mouses either (e.g. Anker, Evoluent). While those do help, it's not enough for me. I get the most relief from an actual joystick vertical mouse.
Not a vertical mouse, but surprisingly good. Only miss mice when playing around with graphics software. I have it in PS/2 and USB, and they did a hack job with the USB hardware, it's very low resolution. PS/2 connector gives a very smooth and nice trackball experience if anyone is tempted.
Turns out it was a micro-injury thing...