I cant quite be sure what your horse has done but my mare bashed her coronet band last year, 1st we knew was when she came up 1/10 lame after a X country event. We paid loads of money on x rays etc which turned up nothing but after a few months off our farrier noticed a slight split growing out of her hoof which he said was probably the cause. After consultation with our vet I was advised NOT to ride her til the split had grown past the bone in her foot as the spilt would cause a temporary weakness in the hoof whilst growing out. I used Cornucresant ( spelling ****!) sticky stuff on her coronet which apparently promotes good hoof growth but be warned it took nearly 9 months to grow out fully. Be advised by our farrier if you have a good one. We use Mike Lowe, Rodway heathfield and Patrick Peacock on our yard and they are top notch with advice and guidance. Good luck xx