Medial branch nerve blocks

Pain caused by the facet nerves

Medial branch nerves are small nerves that feed out from the facet joints in the spine, and therefore carry pain signals from those joints. Facet joint injections are often used to identify a pain source; however, these injections, and other treatments that may be tried, do not always provide lasting pain relief. In such cases, it might be beneficial to confirm that the facet joint is the source of a patient’s pain so that a radiofrequency medial branch neurotomy may be considered for longer term pain relief.

A medial branch nerve block temporarily interrupts the pain signal being carried by the medial branch nerves that supply a specific facet joint. If the patient has the appropriate duration of pain relief after the medial branch nerve block, that individual may be a candidate for a neurotomy. A radiofrequency neurotomy is a type of injection procedure in which a heat lesion is created on certain nerves with the goal of interrupting the pain signals to the brain. A neurotomy should then provide pain relief lasting at least nine to fourteen months and sometimes much longer.

Anatomy of the cervical, thoracic, and lumbosacral medial branch nerves

Facet joints are pairs of small joints that are situated at each vertebral level of the spine. Each facet joint is connected to two medial nerves that carry signals (including pain signals) away from the spine to the rest of the body:

• Cervical medial branch nerves are located in a bony groove in the neck

• Thoracic medial branch nerves are located over a bone in the mid-back

• Lumbosacral medial branch nerves are found in a groove in the low back

These medial or lateral branch nerves do not control any muscles or sensation in the arms or legs so there is no danger of negatively affecting those areas. The medial branch nerves do control small muscles in the neck and mid or low back, but loss of these nerves has not proved harmful.

Medial branch nerve block procedure

As with many spinal injections, medial branch blocking procedures are best performed under fluoroscopy (live x-ray) for guidance in properly targeting and placing the needle (and for avoiding nerve injury or other injury).

On the day of the injection, patients are advised to avoid driving and doing any strenuous activities, and to get plenty of rest the night before.

The injection procedure includes the following steps:

• An IV line will be started so that adequate relaxation medicine can be given, as needed.

• The patient lies on an x-ray table, and the skin over the area to be tested is well cleansed.

• The physician treats a small area of skin with a numbing medicine (anesthetic), which may sting for a few seconds.

• The physician uses x-ray guidance (fluoroscopy) to direct a very small needle over the medial branch nerves.

• Several drops of contrast dye are then injected to confirm that the medicine only goes over these medial branch nerves.

• Following this confirmation, a small mixture of numbing medicine (anesthetic) will then be slowly injected onto each targeted nerve.

The injection itself only takes a few minutes, but the entire procedure usually takes between fifteen and thirty minutes.

After the procedure, the patient typically remains resting on the table for twenty to thirty minutes, and then is asked to move the affected area to try to provoke the usual pain. Patients may or may not obtain pain relief in the first few hours after the injection, depending upon whether or not the medial branch nerves that were injected are carrying pain signals from the spinal joints to the brain. On occasion, patients may feel numb or have a slightly weak or odd feeling in their neck or back for a few hours after the injection.

The patient will discuss with the doctor any immediate pain relief. Ideally, patients will also record the levels of pain relief during the next week in a pain diary. A pain diary is helpful to clearly inform the treating physician of the injection results and in planning future tests and/or treatment, as needed.

Medial branch nerve block results and follow-up

Patients may notice complete, partial or no pain relief during the first 6 to 12 hours after the injection (anesthetic phase). If the area is uncomfortable in the first two to three days after the injection, applying ice or a cold pack to the general area of the injection site will typically provide pain relief.

Patients may continue to take their regular medications after the procedure, with the exception of limiting pain medicine within the first four to six hours after the injection so that the diagnostic information obtained is accurate.

On the day after the procedure, patients may return to their regular activities. When the pain is improved, it is advisable to start regular exercise and activities in moderation. Even if the pain relief is significant, it is still important to gradually increase activities over one to two weeks to avoid recurrence of pain.

Depending on the amount of pain relief the patient has during the first 6 to 12 hours after the injection, the patient may be a candidate for a radiofrequency neurotomy procedure to try and provide longer term pain relief. Generally, a patient must report at least 80% improvement in their pain during the first 6 to 12 hours after the injection to be considered a candidate for radiofrequency neurotomy.

Potential risks and complications of medial branch nerve blocks

As with all invasive medical procedures, there are potential risks and complications associated with medial branch blocks. However, in general the risk is low, and complications are rare. Potential risks and or complications that may occur from a medial branch injection include:

• Allergic reaction. Usually an allergy to x-ray contrast and rarely to local anesthetic.

• Bleeding. A rare complication, bleeding is more common for patients with underlying bleeding disorders.

• Infection. Minor infections occur in less than 1% to 2% of all injections. Severe infections are rare, occurring in 0.01% to 0.1% of injections.

• Worsening of pain symptoms.

• Discomfort at the point of the injection.

• Nerve or spinal cord damage or paralysis. While very rare, damage can occur from direct trauma from the needle, or secondarily from infection, bleeding resulting in compression, or injection into an artery causing blockage.

Patients who are on a blood thinning medication (such as Coumadin^®), or have an active infection, may not be able to have this procedure, and these situations should be discussed with the treating physician. Patients should also let their doctor know of any allergies they have to medications that may be used for the procedure.

By: Ray M. Baker, MD
April 25, 2006