nemo1, I didn't have you figured for CIPD because of the MRI. I suspect it's those discs. Not only can the compress the nerve root, but they lessen the space in the facets--those little joints at the side of each vertebra where the pain nerves exit. Where pain management wanted you to have radiofrequency.
I wasn't thinking sciatica either, interesting that the injection was effective.
https://www.spine-health.com/conditions/sciatica/causes-piriformis-syndrome