Horse joints keep going out of alignment?

I have a 5 yr old Tb mare. She has been passed around a bit because she has a history of intense out of the blue bucking. When I got her she was fine for a few months and I rode her several times. Then all of the sudden she started rearing and bucking again. I had a trainer evaluate her and they said she needed Chiropractic work. So I had the Chiro out and sure enough almost everything was out. she went through 3 sessions, showed improvement and was cleared to go back to the trainer. But she keeps popping out. Her back went out again the moment they started working her. Then after the Chiro came out to pop her back in, the very next morning her Stifle was popping out. You could see when she walked the joint popping. The trainer said she felt that this mare has some type of joint disease and I will have to continue to have her adjusted every time I work her. That just laying down, rolling and getting up can pop her out and require a Chiro visit. They also say they feel this is why she would have the out of the blue bucking (I agree). Has anyone herd of this before? Where a horses joints just will not stay in alignment. All over the body?