Patient Information Sheet

This procedure is performed to investigate the source of lower back pain, which may or may
not radiate into the buttock or legs. This test is to determine whether the pain arises from the
zygapophyseal joints (they are also called the facet joints) of the lumbar spine. The only way
to determine where the zygapophyseal joint hurts i.e. is the source of pain, is to anaesthetize
this temporarily.

The procedure, which is called a medial branch block is therefore a test, not a treatment, and
any pain relief therefore is only temporary – the duration of pain relief varies from patient to
patient and will also depend on the local anaesthetic used.

Before the Procedure

If you think you are pregnant or if you are pregnant you must inform the Doctor before the
procedure as the procedure does involve exposure to X-rays. However, the X-ray dose is
within recommended limits for adults but could be hazardous for a developing foetus.

You must have your usual pain on the day of the procedure. You may need to withhold your
usual medications or even aggravate you pain so that there is sufficient pain at the time of
your appointment. If there is insufficient pain please telephone Southern Cross Radiology
Phone 03 379 0770 and cancel your appointment. The procedure can be performed at a later
date when there is sufficient pain.

Could you please be accompanied by a friend or relative to drive you home after the
procedure as you may feel a little unsteady and so advise you not to drive.

The Procedure

During the procedure you will lie on an X-ray table with the painful side uppermost. You
will be awake and will be able to listen and talk during the procedure. If for any reason you
wish a procedure to stop this is possible, however this is unlikely to be required.

Before the procedure, antiseptic is applied to the skin area of the lumbar spine and a drape is
place over the area to maintain an aseptic area. The X-ray machine is then moved into
position and adjusted so there is a good X-ray of the lumbar spine.

The needle is then inserted into the lumbar area guided by the X-ray machine and during this
procedure it is important that you remain as still as possible as this will shorten the procedure
time. When the fine needle initially pierces the skin there will be a sting and then as it passes
through the muscles there may be further discomfort. When the needle is in the appropriate
position a small amount of local anaesthetic (.3 of ml) is injected around the nerve, which
may cause a slight stinging sensation. This quickly settles. Two needles are required to
anaesthetize one joint and the procedure is likely to take between 15 and 30 minutes.

After the Procedure

If the block has been successful you will note a significant difference in your pain shortly
after the procedure. If however the pain is not relieved don’t be afraid to say so and if only
part of the pain is relieved then it is important that you let us know which part has been

Please remember not to drive following the procedure – arrange for someone to drive
you home.

Risks of Procedure

Allergic reactions to local anaesthetics and to antiseptics. You must tell us before the
procedure starts if you have any allergies.

  • Rarely our patients feel faint during the procedure and if you do please tell the Doctor as the procedure can be interrupted or postponed until you are feeling better.
  • As the local anaesthetic can numb muscles this may affect your sensation of balance and this may last half an hour or rarely until the local anaesthetic has worn off. If you do develop this side effect it is best to focus on the horizon while walking and turn slowly with your eyes looking straight ahead. If you’re unsteady you should not drive a car, nor should you undertake any activity or occupation where balance is essential for safety, e.g. climbing a ladder.
  • There may be a sensation of stinging or soreness where the needles pierce the skin butthis is usually short-lived.
  • Infection where the needle pierced the skin is rare but possible – this procedure is carried out under hospital operating theatre conditions where strict sterile conditions apply – if there was redness, tenderness or any concern about infection please contact me (Dr McLaughlin) as soon as possible.
  • Occasionally following a block there is an initial worsening of pain as the local anaesthetic wears off and for this reason we recommend that you do not undertake unusual activities while the block is having an effect.



Unfortunately research has shown that a single block can be wrong in one in four times and in view of this a further block is required to confirm the initial block. The procedure therefore will be carried out on another day using a different local anaesthetic to confirm the initial block.


If it is proven that one of the zygapophyseal joints is the source of pain then treatment is
available, which will be discussed with you further.

To find the zygapophyseal joint which is the source of pain
Sometimes further diagnostic blocks are required to identify the exact zygapophyseal joint.

If you have any questions about the procedure please contact Dr Mark McLaughlin,
03 337 4839

Important Points

  • Remember this procedure is purely to identify the source of you pain and therefore is not a treatment – so that once the local anaesthetic wears off your pain will return to its usual level and location.
  • Remember this procedure is necessary to identify the source of pain – another entirely different procedure is available for treatment.