Spinal Nerve Root Blocks

Pain originating from a spinal nerve root is referred to as radicular pain. This pain is typically felt in the distribution of the nerve that arises from the root as it radiates away from the spine. In the lumbar spine this is typically along the course of the sciatic nerve and therefore is referred to as sciatica. It may also follow the course of the femoral nerve (femoralgia) with a subtle difference in the distribution of pain in the upper limbs pain is felt in a typical distribution described as brachialgia and follows the specific distribution of specific nerves extending down the shoulder or arm and may extend into the hand. In many patients numbness, tingling, pins and needles may also be felt.

Commonly the pain does not follow a typical pattern and it is the surgeon’s job to try and identify the cause of this pain, which will typically be done with a combination of clinical examination, MRI scanning and possibly also diagnostic blocks.

Nerve pain is caused by either pressure on the nerve at its origin in the spine or from the inflammatory process surrounding the pathology at the nerve root origin. This may be a disc prolapse, inflamed facet joint or cysts and a number of other processes which cause inflammation. Very rarely infection and tumours may be the cause of pain but this is very uncommon. The inflammatory process can not be visualized on scans but is the part of the process that responds to steroids or anti-inflammatory medication such as ibuprofen/ Brufen or voltarol.

Nerve root blocks are performed for two main reasons. One of these is the ability to provide diagnostic information as to the cause of pain. In situations where clinical examination and scans or x-rays do not conclusively identify the source of symptoms, a block of that nerve can assist the process. The principle is that by placing local anaesthetic around the nerve, this should block any pain originating from that nerve.

This means that while the local anaesthetic is working, the pain should improve if that nerve is responsible for the symptoms. Patients are asked to record the pain response in the early post block period and specifically to remember what the early response was.

As local anaesthetic typically lasts for 30 min- 1 hour for lignocaine which is used for cervical nerve root blocks, and for 8-12 hours (marcaine) for lumbar and thoracic nerve root blocks, it is important to recall this early response which may be easy to forget 6 weeks later.

An additional benefit for the patient is the therapeutic benefit from the steroid, which is introduced at the same time as the local anaesthetic. Steroids work simply as long working anti-inflammatories.

Whereas a tablet of ibuprofen typically lasts for 8 hours and therefore needs regular doses three times a day, a steroid injection lasts for approximately 6 weeks after one dose. An additional advantage is that by applying this locally the systemic side effects are reduced and as it is only one dose, the long-term side effects are also reduced. A disadvantage is that the onset of action of a steroid is quite slow so following an injection, the benefit may not be felt immediately.

For these reasons a typical response to a nerve root injection is a short term benefit from the local anaesthetic followed by a recurrence of the pain, although commonly reduced, and then a slow drop in pain over the course of weeks from the steroid.

Procedure:

Nerve root blocks can be performed under local anaesthetic although lumbar and thoracic blocks can be performed under sedation or general anaesthetic if a patient prefers. A very small needle is passed under x-ray control and placed next to the spinal nerve root outside the spinal canal. An x-ray contrast agent is used to confirm the position as being accurate and while this is being introduced an increase in limb pain is often described. This is not severe or concerning and may be helpful as a diagnostic response.

Immediately after the procedure the local anaesthetic can cause numbness and weakness of the affected limb, which causes a temporary limp to develop in the leg. This will make driving unsafe for this 12 hour period so plans should be arranged for getting home from hospital. A follow up appointment should be made for 2 weeks following the procedure.

Risks

This is a safe procedure but specific risks are worth considering. Infection is very rare, but a bruise in the area or a small increase in pain for a few days can occur and is not itself a worrying sign. Due to the presence of the vertebral artery in the neck, a small incidence of strokes is described following cervical nerve root blocks.

This incidence is less than 1 out of every 4000 cases. You should not drive immediately after the injection as the numbness in the limb may impair the ability to drive safely, but this will only last for the day of the procedure. You can return to work the following day.

It is very unusual to have any difficulty with micturition after a nerve root block but should this occur after hours, you should go down to the local A&E department so that you may be seen by the on call spinal team.

Approximately 60-70% of patients can avoid surgery for nerve root pain by trying a nerve root block and the risks associated with this procedure are considerably less than with surgery so should be considered as an alternative where possible.

Post operative course

Immediately after the procedure numbness is usually felt in the leg or arm and this may last up to 12 hours. This will cause a limp in the leg and weakness in the arm so will make driving or work difficult during this time. It is reasonable though to plan a regular day the day after the procedure allowing as much general rest as reasonable to allow the nerve root to settle down and benefit from the procedure. It should not be necessary to take time off work, unless in a heavy manual job.

The original pain may then return although often to a lesser extent than before the procedure. The steroid action may take up to 6 weeks to have a maximal effect. It can be useful to keep a pain diary during this time so as to accurately record the effect of the procedure, as it may be difficult to remember this later down the line.

A follow-up appointment is usually arranged for 2 weeks following the procedure.