Those that have experienced SI soreness and problems, what were the symptoms? I have a gelding that I suspect has some SI soreness. Within the last week he has been reluctant to pick up the right lead, he jumps and pops up when trying to pick it up, kicks his hind end out to the left and most of the time picks up the left lead. He recently kicked straight out when asking for a lope, then seemed to pick up the right lead with no problems (I'm thinking the kick was him self adjusting?). He has always swished his tail under saddle, been very stiff through his shoulders and has a hard time striding out and moving forward in small circles. He has also been kicking his right hind out behind him when standing, like he is stretching it out. He has been seen by a performance horse vet recently and was 100% sound, and has had body work/chiro done. Saddle fit is good and he moves out and looks good when not under saddle and doesn't seem to be sore in his back. I am thinking this is a new issue, but I have never dealt with SI problems so I'm not sure what to look for. I have scheduled an appointment with my vet to rule out kissing spine or other issues, and have a chiro appointment scheduled. Are there exercises or stretches to help relieve sorness in the SI?

Sooo you just described my mare to a T. Reluctant to lope to the right, she took the left lead behind or hopped around. Kicked out once. When she'd finally get the lead correct, it wasn't as relaxed and forward as going to the left. Her body felt stiff but she'd bend and be beautiful to the left. Chiro couldn't find anything, not really sore anywhere, and she passed 3 lameness exams with flying colors.  Lunging she moved fine, picked up the right lead with no hesitation. Thought ok, she's being a colt and testing me, I think by then she had about 90 days on her, but it was spread out between her 2-4 year old years so nothing cosistent. And then one day I asked her to lope to the right and she jsut brake checked me and started backing up. The more I tried forward the harder she'd back or she'd rear. So I let her back up thinking ok, she'll stop in a second. 17 minutes later, of backing in full circles about 10 feet in diameter she finally stopped. And she was shaking so bad I think she only stopped bc she physically couldn't keep going. I knew it wasn't colt **** at that point. I actually have a friend with a Flir camera, so we checked and there was a white spot at the base of her withers. She had been tight there when she'd get a massage, but not painful to the touch for it. So I took her to Wisconsin equine, where she passed another lamenss exam but he said lets xray that spot on the thermal and there was the kissing spine. Did mesotherapy on that, there was no change. So we discussed a vet that was closer to me that specializes in it, and started going there. Injected back, SI, hocks, stifles and she was ok. Still never 100% but injections got me by for 4 months. Finally just did the surgery because it was far cheaper than continuing to inject. But after surgery had to inject everything again besides the back, just to nix compensatory soreness.

It's possible you might be looking at a similar thing. My mare rode fine for awhile and then 1 day it was a disaster. Vet said she probably gritted for the back and then once other things started hurting behind is when she started to act out. So I would defintely rule it out. 

This sounds very similar! I rode him last night, and each time after I asked him to stop he was reluctant to walk forward and would back a few steps before finally going forward. I haven't had him long and I don't have a lot of history on him so I'm still trying to figure him out. He's definitly one to let me know when something is hurting so I don't think it's behavioral at this point. Did the KS surgery fix the issues? I'm hoping it's not KS, but wouldn't be surpised if it was. 

Still doing the post surgery rehab, she was done in February. Was riding ok at walk & trot in May/June. Had her re-injected in the back end like I said above, at her post op checkup. Then got on her for a day & was nice and then she got stupid and hurt her stifle so I just got back on her at a walk last week. So we will see. Before I injected her I was long trotting her for 1-2 laps of the arena each way, and a couple times she voluntarily broke into a lope both directions. So that was enough to tell me I made a good choice with surgery. I had to inject every 4 months and it was $600-1000 each time, depending on what all we were injecting. Surgery was $1500, so financially it was just a lot more sensible 

Usually a sign of sore hocks. And whst he's doing sounds like sore hocks. Sore hocks are usually not going to show in a flexion test.

This part sounds like he might have a mild tie up or PSSM issue. I'd check blood for elevated muscle enzymes.