Diagnosis for croup pain and muscle spasms in a horse's back? My horse is just now coming back into work & I can barely brush him on is croup he hurts so bad. We've had 2 massages.

He shows no lameness in his walk, trot or canter, but he tucks his tail when i brush him or directly touch his croup muscles like he expects it to hurt. But solid strokes he isn't phased, even with a massaging ball. I'm wondering now if he's doing it from a learned behavior because maybe it used to hurt but doesn't anymore or if he really is in pain. I just don't know what to think anymore.
Yes, he loves the stretches. I've been stretching him every time I take him out. I got him three months ago and whenever I purchased him he'd just been brought back into work. He passed all of his vetting but was noticed to be sensitive on his croup but they said just to stretch him but since then it's gotten worse. My massage therapist says his muscles need rehab which is what we're doing but I was curious of the chances of it being an SI joint problem. Just not sure what else to research or if anyone else has had experience with this. He's been acting like a bully on the ground when put on a lunge line and yesterday he didn't even want to walk forward when I rode him and he bucked for the first time at the trot when I asked him to work but he wasn't nearly as sore as he has been so now I can't tell if it's behavior or pain. I've tried to give him the benefit of the doubt but his attitude continues to get worse while his back stays the same.
What did your massage therapist say? Will he willingly perform back stretches?(the kind done from the ground with a carrot)? What caused him to be out of work?
Well my question is advice on what it could be-- not advice on what to do. I would like to research possible causes before I spend $300 on an X-Ray and then it actually turns out to be a muscle problem or viseversa.
Make sure you get a vet out!! For now give him bute or bute-less it’s like Advil for hores
I've done research on SI joints and he's had two massages so far and he's not lame at all, just sensitive and sore. But I figured the pain has to be coming from somewhere I just don't know where
i think you should get a vet as soon as you can! it can be a big injury
get a vet out asap
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