I don't know that I am on the bandwagon yet, but it is very common for them to do them here for hind end lameness. They seem to do them when horses are NQR and the lameness can't be attibuted to something else. They seem to be moving in the direction of maintenance injections like hocks.
That said, when my mare was rehabbing from suspensory surgery, she reached a plateau and was still lame/sore, and the vet found that she was VERY sore in the SI area. Had the joints injected on both sides, with immediate improvement, and a few months later redid the left one. This was in late 2010/early 2011, and she has not needed SI joint injections since then.
It's a tricky procedure and really should be done with live ultrasound as it's difficult to get the needles in the right place. The cost was about the same as hock injections.
Thanks for your responses so far. My horse is out on lease and will be until April. He has been with them since July 2011 and is at a very reputable barn so I would think/hope the vet is good. The leasee has contacted me about this and has offered to pay for the procedure with my consent. I thought that a sacrum injection sounded weird - must be the SI!
So, do you think the SI procedure may be too risky? Maybe I could ok the hocks and hold on the SI.
I really appreciate your input. Even though my horse is on lease he is still my baby!
Both can be routine for high performance horses or horses that just have general wear and tear or injury (especially in the case of the SI injections). They are not risky in general, most good equine vets will have done plenty of them. If a vet is recommending this and the person leasing your horse is willing to pay then why not if it could potentially help your horse to stay sounder longer? It is not as common to inject the SI but certainly no more risky than any other injection....have seen it done a number of times. It's honestly not a big deal and can make a huge difference to your horse.