Oh for goodness sakes - some "Resolve wound" junk is going to do AFA for a tendon issue... I thought blatant advertising was forbidden on this forum??
Anyways - I have seen/heard of some similar issues in horses. Most resulting in euthanasia for various reasons. The main one being infection. Looks like you've circumvented that - which is not an easy feat.
It looks almost like the fetlock needs to be supported from underneath with a foam block. If you wrap it and then duct tape a foam yoga block or something underneath... I would also get this horse on the appropriate medications to strengthen/tighten the tendons and ligaments (name is escaping me). Used mostly for foals who are too loose up front. As well I'd be keen on immobilizing the horse until this is sorted (box rest). And I do agree that a second/third opinion needs to be formed.
BUT that being said - you have to first decide the lengths you are willing to go to. I know it is difficult in the moment to make the decision to euth a happy and otherwise healthy horse but things can take a turn for the worse very quickly and if you have 5, 8, 10 thousand invested in vet bills at that point and the horse is then suffering - it is not a good feeling. I wish you the best of luck and hope a fresh opinion from another vet will help set you on your way!! I know my vet (who is also excellent) does have other vets he refers to professionally in cases that he is not 100% sure on, and with high stakes cases. I don't see why a collaborative effort cannot be a good thing in this situation.
They say money doesn't buy happiness -- well happiness doesn't buy horses!