I used to always get skier's thumb and it took me about 10 years to find out why.
If you're a park rider, you're not getting it because of how you put your pole straps on. You are getting it from falling on hard landings. It's reflex to put your hands out to catch yourself from falling. Then, since your pole is still in you hand, the tip of your thumb pushes against the snow while the pole acts as a fulcrum. With all that instantaneous torque on your thumb, somethin has to give. The icy landing stays icy. The metal pole stays metal. And your bone (or ligament) breaks.
To stop it from happening, you have to retrain yourself on how to fall. You got two options:
a) Keep your thumb holding onto your pole when you fall. Hence the duct tape suggestions. Or train yourself to hold on to your poles and keep a tight fist whenever you fall.
b) Let go of the poles when you fall. I think this would be a bit harder to train yourself to do. And if you do it too late...well fuck...now you got skier's thumb again.
I guess you could also stop riding park:)
Good luck man, that shit bites. But google images says you're in good company:
