I'm doing a bit of research on this to try and help you out.
I still think contacting a few vets and farriers and barefoot trimmers are your best bet though.
I found this on this website The Lazy Horse, Club Foot & Knock-Knee Foal
Knock-Knee Foal |
"I have a foal with knock-knees," writes John Marsh of North Carolina. "Both knees are so bad that they hit together when he walks. Is it possible that keeping the hooves properly cut could help straighten the knees? I have ordered a knee brace. Have you heard any news (good or bad) about knee braces for this problem?"
Foals with severe knock-knees may be helped by trimming the outside heel and quarter of the hoof wall lower then the inside hoof wall, and squaring the toe of the hoof wall. But you can accomplish only a limited amount with trimming alone.
Other things you need to do are: exercise the foal twice daily by hand walking it for 15 to 30 minutes; massage the legs, top to bottom, for 10 minutes each leg; ice-bag the knees for 15 minutes to help with pain and swelling. You can make an ice bag by combining one cup isopropyl alcohol to three cups water in a Ziplock-type bag and freezing it overnight. The result is a nice cold ice bag that is not solid, so will form to the knee. Wrap the ice bag with terrycloth, so as not to injure the horse's skin.
Knee braces, if designed to help this problem, will probably help. I have not seen any long-term study on their use, but I would be concerned that prolonged use of braces could weaken the knees. Other options to consider with your vet are surgery, epiphysial stapling, and casting.
That was with a foal, but with your yearling, as Luv2ride mentioned it could be too late to fix it.