Dr. Moldover: ESI

Epidural Steroid Injections

The epidural space is the space between the sack containing the spinal fluid, spinal cord, and spinal nerve roots, and the bony spinal cannel. Think of a cylinder inside another cylinder: the epidural space is the space between the two cylinders. The inner layer (the dura) covers the spinal nerve roots as they leave the spine to form the sciatic and other major nerves. This membrane can be inflamed by chemicals released by a disc herniation, or can be irritated by bony overgrowth in spinal stenosis. The corticosteroid injected into the space relieve this inflammation, just like a steroid cream (hydrocortisone) relieves the inflammation of a red skin rash. There are 3 ways to perform an epidural steroid injection:

Interlaminar epidural steroid injection: This is the traditional approach in which a special needle is placed between two lamina (the bony plates covering the back of the spinal column). A small amount of air is injected during the advancement of the needle. As the needle tip enters the epidural space there is a sudden loss of resistance which tells the injectionist to stop before the needle punctures the sack of spinal fluid. This is the technique used for epidural anesthesia during childbirth or surgery. It can be performed without the x-ray guidance, but is less useful as a diagnostic tool in that case.

Transforaminal epidural steroid injection: this technique is preferred if the symptoms, physical findings, and imaging studies point to a single nerve root as the primary pain generator. A thin needle is inserted into the small cannel through which the nerve root leaves the spinal column. This allows precise identification of the pain generator, and the application of a smaller amount of steroid where it will do the most good. A C-arm is essential for this technique. If good temporary relief is obtained but the relief does not last long enough, then the nerve can be treated with pulsed radiofrequency. This can be done by performing the injection with a special insulated needle through which a radiofrequency probe can be passed. The nerve is then exposed to an intermittent (pulsed) radiofrequency current. The pulsing prevents heat from damaging the surrounding tissues. The radio waves alter the function of certain genes in the nerve cells which changes the way they transmit pain sensations. The effect lasts from 4 months to several years. One year is average.

Caudal epidural steroid injection: This is an old technique in which a needle is inserted up through the base of the spine into the space inside the sacrum (the base of the spine). Medication can be injected to cover the bottom 1 or 2 spinal segments. It is useful in cases where previous surgery, especially fusion, makes the other approaches technically difficult. X-ray guidance is again optional, but allows for manipulation of the needle to produce better flow of the medication into the desired part of the spine.