Sadly I can't interpret x-rays but you might have better luck if you post this in the "Horse Health" section of this forum. Meanwhile what did your vet say? Only other recommendation I can make aside from that is it sounds like you may need to go to your nearest vet school for a lameness evaluation. My experience has been that it's not neccesarily much more expensive than having your vet look at them---it's just the inconvenience of getting there. Meanwhile you'll have access to top notch vets and advanced diagnostic techniques (granted, those may get expensive!).