Take a good look at this picture.
Does your horse care about saddle fit? Does your horse care about the rider's balance? Who was crooked first, the rider or the horse? Who is responsible for influencing the balance of the horse?
Can a horse correct it's own crookedness?
Do all horses know how to carry a rider in balance?
Do all horses know how to balance themselves correctly?
Who's job is it to maintain and check tack?
Who needs to know their own body bio-mechanics as well as the horses? What do you do as a rider when your horse refuses to move forward? What muscles should the horse be using?
What muscles build the topline of the horse? What muscles should the horse be suppling?
Does an ill fitting saddle create a willing or sour horse?
Are you running into training issues or pain issues?
What will inevitably happen to the rest of the body if the back is unable to function correctly?
Can a horse be willing, balanced, and supple without all of the above issues being addressed?
Once you know there is an issue, is it fair to continue with the same work load without making some changes?
How long does it take to heal from these issues? What deep physical damage occurs from these issues? What emotional/mental damage occurs from these issues?
How do you find the right help to untangle the aftermath?