Nerve root blocks

Your doctor has requested that you have  a nerve root block to help diagnose the cause of your pain. We hope that the following information will answer some of the questions you may have about this procedure.

What is a nerve root block?

Nerve roots exit the spinal cord and divide into nerves that travel to your arms and legs. These nerve roots can become inflamed due to pressure from nearby bone spurs or  intervertebral discs. Inflammation of nerve roots may cause pain in the back, neck/arms and/or the legs. A nerve root block provides important information for your doctor and may also provide you with some relief from pain.

Why do I need to have a nerve root block?

The procedure is designed to prove which nerve is causing your pain by placing temporary numbing medicine over the nerve root of concern. If your pain improves after the injection then that nerve is the most likely cause of your pain. If your pain remains unchanged, then that nerve is probably not the cause of your pain.

What is injected around the nerve root?

The injection is a combination of local anaesthetic (a numbing agent) and steroid (an anti-inflammatory agent). The local anaesthetic works immediately and the steroid usually begins to work within two to three days but may take up to a week.

How do I prepare for a nerve root block?

You can continue to eat and drink as normal. 

If you are diabetic please inform the doctor before the examination as there is a possibility that your sugar levels will vary after the injection. It is important that you continue to monitor your levels carefully for several days and consult your GP if necessary.

You can continue taking your normal medication. If you are on any medication which thins the blood (e.g. aspirin, clopidogrel, warfarin, rivaroxaban, dabigatran, apixaban) we ask you to call the Imaging department on 0117 414 9110 as we may need to adjust your medication before undergoing this procedure. These may need to be adjusted to keep the risk of bleeding to a minimum.

The procedure uses x-rays and the amount of radiation used is small, however if you think you may be pregnant please inform the Imaging department before attending the appointment.

Afterwards your leg may feel numb or weak and you should not drive for 24 hours. You will need to arrange for someone to take you home. We advise against using public transport.

What will happen during the procedure?

  • You will arrive at Gate 18 whereby a member of the Imaging team will take you through to the fluoroscopy waiting room.
  • Following confirmation of your details and history you will be shown into the x-ray room and introduced to the staff performing the procedure. You will be cared for by a small team including a radiologist (x-ray doctor) and/or radiographer and an imaging support worker.
  • Before the examination begins the radiologist or specialist radiographer will explain what they are going to do. You will be given the opportunity to ask any questions you  may have. If you are happy to proceed you will be asked to sign a consent form.
  • You will then be asked to lie on your front on the X-ray couch. The skin will be cleaned and a small amount of local anaesthetic will be injected under the skin. This stings for a few seconds and the area then goes numb.
  • A very fine needle will be directed just next to the nerve root using the X-ray machine. Sometimes the needle can touch the nerve itself in which case you may feel a sharp pain going down your leg. This will only last for a second or two. A special dye called contrast medium is then injected around the nerve root. This shows up on the X-ray machine to confirm the needle is in the correct position. When the radiologist or specialist radiographer is satisfied with the needle position, the local anaesthetic and steroid will be injected along the nerve root.
  • Afterwards you will be asked to sit in our waiting room for 20-30 minutes so that we can ensure you are feeling well before you go home.

How long will it take?

You will be awake throughout the procedure, which lasts about 15–30 minutes.

Will it hurt?

You may feel a little pressure or discomfort, which may travel down the leg, during the injection of the local anaesthetic and steroid. This will last for only a few seconds.

Afterwards your leg may feel numb or weak for up to 24 hours. You will be asked to wait for 20 to 30 minutes before going home.  As your leg may feel numb or weak, you should not drive for 24 hours and you will need to arrange for someone to take you home. We advise against using public transport. 

Some people find that their pain feels worse for two to three days after the procedure. This is because the steroid can sometimes irritate the nerve. Do not worry if this happens, as it will settle down by itself. 

If your leg becomes numb you may need someone to stay with you overnight.

Are there any risks associated with a nerve root block?

Generally it is a very safe procedure. Potential complications are uncommon and include:

  • An increase in your pain in the first 24 hours following injection. Should this occur, take your usual or prescribed pain medication and seek advice from your pharmacist or GP if necessary.  
  • Bleeding or haematoma (a bruise under the skin) – this should settle down by itself.
  • Infection developing at the injection site. This will happen to less than 1 in 5000 people. Contact your GP if you experience any redness or tenderness at the injection site.  
  • Flushing of the face for up to 48 hours after the injection – this should settle down by itself.
  • Skin dimpling or discolouration at the site of the injection – this should settle down by itself.
  • A disruption in your mood – this should settle down by itself.
  • Occasionally a change in menstrual cycle may be experienced. This is most likely due to the steroid but contact your GP if this happens to inform them.  
  • If you are diabetic you may notice a rise in your blood sugar levels. It is therefore important you monitor your levels carefully for several days after the procedure and consult your GP if necessary.
  • The procedure uses X-rays to confirm that the needle is 
    in the correct place. The amount of X-rays used is very small however patients who are or who may be pregnant should inform the department before attending for their appointment.


We hope this information is helpful. If you have any questions either before, during or after the procedure the staff in the Imaging department will be happy to answer them.
The telephone number of the X-ray department can be found on your appointment letter.


Overview | Low back pain and sciatica in over 16s: assessment and management | Guidance | NICE [Accessed January 2024]

British Association of Spine Surgeons - Booklets [Accessed January 2024]

How to contact us:

Southmead Hospital, Bristol, BS10 5NB

0117 414 9110


If you or the individual you are caring for need support reading this information please ask a member of staff for advice.

© North Bristol NHS Trust. This edition published January 2024. Review due January 2027. NBT003237

Nerve root blocks