An epidural steroid injection is the most common technique. The spinal (nerve) cord is surrounded by the dura mater, a tough fibrous covering.
Outside the dura is the epidural space, the space outside (epi-) the dura. It is here the steroid is injected directly, into the area containing the cerebrospinal fluid.
A local anaesthetic is given by injection into the skin of the back first, to numb the pain of the epidural injection itself.
The effect of epidural injections
Epidural injections reduce inflammation from common conditions such as spinal stenosis, disc herniation or degenerative disc disease. It is possible that the injection helps to remove or flush out inflammatory proteins from around the structures that may be causing pain.
Success of epidural injections
An epidural steroid injection may be successful in relieving lower back pain in about 50% of patients. The effects tend to be temporary , eg one week to a year, an epidural can provide pain relief for patients during an episode of severe back pain. This allows them a window to push forward with their exercises and progress in their rehabilitation.
The frequency of epidural injections
There is no evidence which indicates how often epidural injections should be given but a maximum of three injections per year is thought reasonable. It is not clear whether a series of three injections should be given, but if one or two injections help, the doctor may save any more in case the pain recurs.
The risks of epidural injections
There are very few risks with epidural injections. Examples are: the epidural needles by pierce the dural sac into the cerebral spinal fluid (CSF). The CSF may leak and give the patient a spinal-related headache.
Introduction of infection into the epidural space is a remote risk. The person cannot be paralysed as the spinal cord ends higher up in the spine from the injection site, it is possible to damage a nerve root. This could result in loss of muscle power or feeling in an area of the lower body.
When epidurals are not performed
Epidural injections are not be performed on patients whose pain is from a tumour or infection. Any suspicion of a non-mechanical cause indicates the need for an MRI scan to make the diagnosis more secure.