When my vet and I diagnosed my horse with SI pain, we did so by way of flexion tests and by blocking every joint till SI was the next joint. The only other potential problematic joint was the hip, and there was little we could do to treat that pain. I originally called for the lameness exam because my horse was not stepping under herself evenly. Her left (? it’s hard to remember now) hind leg wasn’t swinging and the stride was very short. So we guessed SI and did the injections on both sides. There was absolutely no improvement. The next step in diagnosing the problem was a bone scan, and that just wasn’t in my budget for this horse. It made me very sad, but I eventually just retired her because the only thing improving the lameness was rest.
I suppose my point is this: You’re dealing with a tricky problem that can quickly become expensive to diagnose and treat, if treatment even works. Some people sing the praises of SI injections, but I have not had success with them when treating pretty prominent lameness at the trot. Maybe my horse had hip problems and thus the SI wasn’t the problem, so injections logically didn’t work. In the end, my guess is that there was arthritis that just couldn’t be managed with the amount of work I wanted this horse to do.
