Sore hind end on horse?

If I were you I'd find a very experienced and knowledgeable massage therapist and get him or her to come out along with a different chiropractor - one who has is a DVM with separate training in chiropractic. It's either skeletal or soft tissue. No other choices. If you can find a good lameness vet - one who specializes in lameness, that would be an option, too.