Arthrography code selection is limited to joints such as ankle, elbow, hip , knee, sacroilliac, shoulder, temporomandibular, and wrist.
76499 Unlisted diagnostic Radiographic procedure
The above code I thought you could use and compare to possibly 72275 or one of the codes for the joints that might be similiar in size.
For the injection procedure, I am not sure if 64490 would be appropriate or not. Since the new facet codes came out I have seen any articles if these codes can be reported for injection at the joint location you mentioned.