That's exactly what Estrone should be used for! It really helps the hot ones settle too, so as long as you don't have a competition coming up and it's being used for "rehabilitation" it's a great vet-recommended option. It's great to use in conjunction with long-and-low and pole work as it really helps supplicate the weaker muscles and helps build a better topline.
Hope the OP won't mind me bumping up this fairly recent discussion re: SI issues.
Will try to summarize....My mare (mentioned earlier in this thread) has just passed the 1 year mark post SI injections. The injections worked fabulous for her, we did the rehab, started back slow and had a great summer/fall. We weren't able to ride enough this past winter, she lost condition and in a post layoff lesson seemed to have started developing problems again. They did not initially seem to be in her SI (different symptoms) so attempted acupuncture treatment, turned out to be an $1100 disaster, attempted bowen-ish/muscle release treatment (summarizing), not sure how much that has helped but now her issues are more obviously SI like. I don't lunge this horse often (not positive she is hoping behind or disuniting but she is not keen to carry at the trot and is trying to break into canter). I am currently walking her in hand and/or under saddle for approx. 20 mins without her minding too much.
Wondering of those who've had their horses done, and are seeing their symptoms returning, or those who've had to return from another period of layoff, have you had success repeating your back to work rehab problem again and strengthening the horse without further injections?
My regular chiro (who has often fixed my horse in the past) has become entirely unreliable...disinterested in being a vet any longer (??? I'm not sure) but I have little faith she will help me resolve the issue at this point. I do know what I want to do but the $1100 vet pay I'm currently paying off has me seeking alternative ideas...