I just saw almost this exact same discussion in another thread and I also said to bill 20610 but I was completely overruled by the other coders. This is the answer that was given:
Per CPT 2012, if a SI joint injection is done without any guidance, then 20552 should be used instead. The reason for this is that based on studies that have been done on epidural injections and SI joint injections, there are certain sites that have been deemed impossible, or near impossible to target accurately without guidance (which is why 77003 is included in the facet, transforaminal epidural, and SI codes). Therefore if guidance is not used, then the thinking is the doctor is not actually performing an SI injection (because you can't hit the joint without visualization), so it must be an injection of the surrounding tissue (i.e. muscles/trigger points).
