An epidural steroid injection is an injection literally in the epidural space. "Epi-" is Latin for "outside of" and "-dura" is the "lining of the nerve root." So, an epidural steroid injection is literally an injection in the epidural space.
We use epidurals for a variety of reasons in the spine. We use them for diagnostics - sometimes we put medicine around a certain nerve root in order to determine whether or not it is the source of pain. And we often also use them for treatment - to reduce the inflammation and the swelling around nerve roots and sometimes the disc.
An epidural steroid injection in the lumbar spine can be accomplished three different ways. There are three different ways to get the medicine to the epidural space, I should say. One of the older ways is to do what is called a 1) Caudal Epidural Steroid Injection. So, here's the lower back. You can do a caudal where you come in from the very bottom of the spine and you push the medicine up. You can get to the epidural space by doing an 2) Interlaminar Epidural Steroid Injection. An interlaminar injection is where you basically come from the back of the spine - you pop through a ligamentum flavum and you put the medicine from the dorsal aspect - or from the back of the spine and allow it to flow forward. And then you can do what's called a 3) Transforaminal Epidural Steroid Injection. The transforaminal epidural steroid injection for a lot of cases is going to be the preferred method of getting the medicine in, but it does depend on the pathology that you are trying to treat and the underlying anatomy. A transforaminal epidural steroid injection is, basically, coming next to the foramen. So, you are coming from the side of the spine, and you're putting the medicine next to the nerves as it exits through the foramen. And those are the three ways to enter the lumbar epidural space.
In the cervical and thoracic spine, there are two ways of getting the medicine to the epidural space. There's the interlaminar from behind and then the transforaminal coming from the side.