Erector Spinae Plane Block for Acute Back Pain in the Emergency Department

The goal of this clinical trial is to learn if an erector spinae plane block (ESPB; a type of nerve block) works to reduce pain in adults presenting to the emergency department with low back pain. It will also learn if the ESPB reduces pain, disability, and return to work at 7 days. The main questions it aims to answer are: 1. Does the ESPB reduce short-term pain in participants with low back pain? 2. Does the ESPB reduce longer-term pain, reduce disability, and improve return to work and activities in participants with low back pain? Researchers will compare ESPB to a placebo (an injection that does not involve a nerve block) to see if ESPB works to treat low back pain. Participants will: Receive either the ESPB or a placebo injection in the emergency department Report their pain scores for up to 120 minutes Report their pain, disability, and return to work at 7 days