Renee
Have you heard of De Quervains tenosynovitis? My OH has this ( rather frustratingly as he is the one renovating the house and doing most of the animal work). He can do most things, but there is a position (e.g. getting mobile phone out of top jacket pocket) which is agony on wrist, that and lugging up our water containers over his shoulder. Ibuprofen helps, but not if he has over worked it doing something...., Apparently the issue is a particular tendon position.
I have just got him a brace, also used for skier's thumb, which he says is helping. It stops him over using his thumb.....I only wondered as you mentioned solitaire, which is another non-load baring twisty thumb/wrist movement....Not sure if you could knit in it though....I could always ask him to try
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Jo