An epidural steroid injection (ESI) is a minimally invasive procedure that helps relieve neck, back, arm, and leg pain caused by inflamed spinal nerves that can be caused by spinal stenosis or disc herniation. Medications are delivered to the epidural space, which is a fat-filled area between the bone and the protective sac of the spinal nerves. Pain relief after an epidural injection may last from several days to years. The goal is to reduce pain so that you may resume normal activities.