Without procedure codes to check and see if there are any NCCI edits for billing the fluoro and ultrasound can be billed together, my thought is that these both are likely able to be billed on the same DOS.
However, I work for an insurance company and at some point, we would likely question the medical necessity of performing these joint injections with both fluoro and ultrasound when it isn't the standard practice.
What is the medical necessity of your provider using both of these imaging modalities when performing joint injections? This sounds ripe for an audit from an insurance carrier perspective if your provider is routinely billing for both these services with the joint injections.