Does anyone know if there is a specific code for this procedure, or do I need to do some creative coding?
I would need more detail on how you performed this procedure to code accurately.
Did you inject the sacrococcygeal joint, or a non-fused remnant disk in the coccyx itself?
20550 for a ligament injection is a possibility, but it sounds like you did a sacrococcygeal joint injection, in which case you could use 20605 (intermediate size joint injection), which pays about the same. Depending on the carrier, you could try asking for more money with a 64999 (unlisted code), if you have a good staff that will follow up on this.
It does not sound like you did a muscular injection, so I would NOT use 20552. Also sounds like much more work than a 20552, and you don't want to short change yourself. From a compliance perspective, if your intention was not to do a sympathetic block, then I would not code it 64520.
The CPT Assistant Archive is a wonderful resource for coding questions and is around $300 per year. Cheaper for AMA members. You can order back issues of the newsletter as well to have documentation to send to insurance companies when they try to down code you.
http://www.ama-assn.org/
Another great resource for AMA members is to be able to ask 5 free coding questions per year. You type your question with as much detail as possible and someone from the AMA writes you back an answer within 14 days. Then you put a copy in your Compliance folder and refer to it if anyone questions your coding.