No injection. Epidural steroid injections are not an indicated treatment for a lumbar sprain/strain!
A Needle. Insertion of a needle between the protruding spines of the vertebrae into the epidural space (no nerves) and medicines are injected into the epidural space.
Safe procedure in. Experienced hands. They will take you into a room with a fluoroscopy machine, which is a c shaped x ray machine that they can maneuver around you. They will take some pictures, put a needle in your back, position it correctly with x ray, and then put the medication in the epidural space (assuming translaminar) if transforaminal, will be slightly to the side. Procedure will be maybe a few minutes.