Hiking with Cast for Gamekeeper's / Skier's thumb

I jabbed my thumb last fall. I went to my primary doctor. He took an xray and did not find anything. 4 months later the pain was continuing and was shooting down my forearm.

I went to an orthopedist, and he referred me to a surgeon because "it was too late for it to heal on its own"...the joint is unstable and/or there is a ligament detaching from the bone.

So I have to have surgery and wear a fiberglass cast from forearm to thumb, 4 fingers free, for most of the winter.

Any ideas on how to keep my fingers from freezing off?

I had the same thing but discovered it a week after the injury. I only had to wear a cast for a month as I remember. Anyway, socks. Of varying degrees. Never found anything waterproof. But an empty bread bag between socks works for that.