Facet joints are pairs of small joints that are situated at each vertebral level of the spine. A facet joint may also be called a zygapophysial joint or a Z-joint. Medial branch nerves are small nerves that feed out from the facet joints in the spine and carry pain signals from the facet joints to the brain. Each facet joint is connected to two medial nerves.
The medial nerves are uniquely located in each segment of the spine:
A medial branch nerve block is a procedure in which an anesthetic is injected near small medial nerves connected to a specific facet joint. Typically several levels of the spine are injected in one procedure. If the patient experiences marked pain relief immediately after the injection, then the facet joint is determined to be the source of the patient's pain. The procedure is primarily diagnostic, meaning that if the patient has the appropriate duration of pain relief after the medial branch nerve block, then he or she may be a candidate for a subsequent procedure - called a medial branch radiofrequency neurotomy (or ablation) - for longer term pain relief.
As with many spinal injections, medial branch nerve block procedures are best performed under fluoroscopy (live X-ray) for guidance in properly targeting the nerves, placing the needle, and avoiding injury.
The medial branch injection procedure includes the following steps:
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 in the recovery area for 20 to 30 minutes. The physician will then ask the patient to perform some movements or activities that would usually provoke the pain. This assessment is done in order to determine if the medial branch nerve block has reduced the patient's pain.
Potential risks and/or complications that may occur from a medial branch injection include:
Depending on the amount of pain relief the patient has during the first 4 to 6 hours after the injection, the patient may be a candidate for a radiofrequency neurotomy (radiofrequency ablation) procedure to try and provide longer term pain relief. Generally, a patient must report at least 80% improvement in their pain during the first 4 to 6 hours after the injection to be considered a candidate for radiofrequency neurotomy.
In cases where a medial branch nerve block has confirmed that a patient's pain originates from a facet joint, a radiofrequency neurotomy can be considered for longer term pain relief. A radiofrequency neurotomy is a type of injection procedure in which a heat lesion is created on the nerve that transmits the pain signal to the brain. The goal of a radiofrequency neurotomy is to interrupt the pain signal to the brain, while preserving other functions, such as normal sensation and muscle strength.