At the beginning I used to think not, but now I honestly think they are related. I think beowulf had some commments about it and that’s been my personal experience. If I had to guess, there are just structural issues in her conformation (likely starting at the hoof - mild NPA, low heels) that leads to the back issues which then makes her more injury prone and anxious (likely because of pain).
To be clear she is rideable (although a very difficult ride that is go-go-go) and doesn’t buck, bolt or rear but whenever I’ve started putting her into serious work she has broken down one way or another. I think if I’m ever going to pull her out of the field I’ll likely just have to accept that she’s gonna be a very difficult pleasure ride that hopefully mellows out with years.
Since I have another one that somehow went from a husband horse status to a pretty promising jumper that also happens to be just an all around fantastic animal it’s easier for me to accept that the KS mare’s career will likely never amount to anything. I have debated putting her down because selling her is just asking for a bad ending given her tough rideability, hate for trails and health issues. But, for now while we can afford it she is just in early retirement at the age of 11.
Also just wanted to add… I’d not underestimate the emotional angst you will put yourself through when your horse is NQR almost all the time. The saddle fit for starters… The difference between a fair fit to a pretty good one on my non-KS horse is barely noticeable - might move and jump a bit better and give a better bend. On that mare it is a difference between a meltdown and an OK ride. Then the back changes and you’re back at square one!
Then the hooves… I had to go barefoot because she stopped growing feet and there was nothing left to nail on. Then we put on casts but she kept pulling those off. So I scrambled to get her boots in the right size. Then the boots started rubbing. So we had to rip off the bandaid and she was hobbling around for 2 months off work until her hooves toughened up. How do you even correct angles on a horse that does not grow feet even when she’s on farrier formula and all the other good stuff? And her feet were not that bad for an OTTB. In short, complete and non stop nightmare!