Selective nerve root blocks are mostly used to diagnose the specific source of nerve root pain.
The nerve root
The nerve root is the main nerve which exits from the spinal cord through the intervertebral foramen, a position which renders it vulnerable to disc, ligament and joint changes.
Nerve root pain
Whilst nowhere near as common as low back pain, the incidence of nerve root pain (leg or arm usually) is high enough to use nerve blocks to diagnose and treat this problem.
IF a nerve root is compressed and inflamed it can produce back and/or leg pain. The cause of this problem may not show up on MRI scan so it may not clear which nerve is causing the pain. This is where a nerve block of specific nerves can help decide which nerve is at fault.
The nerve block
The nerve block is performed where it exits from the intervertebral foramen, and a steroid (an anti-inflammatory drug) and lidocaine (a painkilling agent) is usually injected. The anaesthetist uses fluoroscopy (a form of live x-ray technique) to see exactly where the medication is being delivered.
If the patient’s pain goes away after the injection, the anaesthetist can assume reasonably that the nerve root he has just blocked is responsible for the patient’s pain.
Success rates vary and are generally not clear, and as with epidurals, nerve root blocks are limited to a maximum of three a year.
Nerve block injections are technically more difficult to perform than epidural injections and best performed by experienced practitioners. As the injection is right next to the nerve root, a block can sometimes worsen a person’s leg pain.