Chronic neck pain often presents a diagnostic challenge for physicians. A Cervical Medial Branch Block (CMBB) is a specialized procedure used to identify the source of this persistent pain. This diagnostic injection targets specific nerves that transmit pain signals from small joints in the neck. By temporarily numbing these nerves, physicians can determine if the pain originates in the facet joints, guiding future treatment decisions.
Understanding the Target Nerves
The cervical spine consists of seven vertebrae, with small facet joints located between each pair. These joints provide stability and allow movement but can develop arthritis or mechanical stress, causing chronic discomfort. Pain signals from the facet joints are transmitted by tiny nerves known as the medial branch nerves, which are branches of the spinal nerves.
These medial branch nerves exclusively carry sensory information from the joints to the brain. The CMBB targets these small nerves, not the main spinal cord or the larger nerve roots controlling movement or sensation in the arms. Since each facet joint is typically innervated by medial branch nerves from two spinal levels, the injection must target the nerves at both corresponding levels for effective numbing.
The Primary Goal of the Injection
The primary purpose of the Cervical Medial Branch Block is to confirm if the facet joint is the generator of a patient’s chronic neck pain. As a diagnostic test, a local anesthetic is injected near the medial branch nerves to temporarily interrupt their ability to send pain signals. If the facet joint is the source of the pain, the temporary nerve block should result in significant pain reduction.
The clinical standard for a positive diagnostic block is defined as the patient experiencing 50% or more pain relief while the anesthetic is active. This temporary relief confirms the facet joint as the pain source. Because individual pain response varies, the procedure is often repeated on a separate occasion using a different anesthetic to confirm the results and minimize the possibility of a false positive. Isolating the source of the pain allows the physician to move forward with targeted treatment.
The Procedure and Post-Injection Care
The Cervical Medial Branch Block is performed in an outpatient setting, typically taking about 15 minutes, though patients should plan for an hour for preparation and monitoring. The patient is positioned, and the neck skin is cleaned with an antiseptic solution. A small amount of local anesthetic is first used to numb the skin.
The physician uses live imaging guidance, such as fluoroscopy or ultrasound, to ensure accurate needle placement. This imaging allows the provider to safely navigate the fine needle near the bony landmarks marking the medial branch nerves. A contrast dye may be injected before the anesthetic to confirm the correct spread of medication away from surrounding vessels and nerves. Once positioned, a small volume of anesthetic is injected around the target nerves.
Following the injection, the needle is removed, and a small bandage is placed over the site. The patient is monitored for 15 to 30 minutes before being discharged. A driver is required, as the procedure can cause temporary numbness or lightheadedness, making driving unsafe. Post-care instructions are provided, along with a pain diary instructing the patient to record the level and duration of pain relief.
Post-Injection Care Instructions
- A driver must be present for discharge.
- Avoid strenuous activity for the remainder of the day.
- Do not soak the injection site in a bath for 24 to 48 hours.
- Record the level and duration of pain relief in the provided pain diary.
Interpreting the Outcomes
The physician uses the pain diary information to interpret the results. A “positive block,” where the patient experienced significant temporary pain relief, confirms the targeted facet joint as the cause of chronic pain. This positive result often leads to the recommendation of radiofrequency ablation (RFA).
RFA is a therapeutic procedure that uses heat generated by radio waves to temporarily destroy the medial branch nerve tissue, preventing pain signals from reaching the brain. RFA can provide longer-lasting relief, typically ranging from six months to over a year, because it targets the confirmed pain source. If the CMBB results in a “negative block” (little to no pain relief), the facet joint is likely not the source of discomfort. The physician will then investigate other potential causes of neck pain, such as issues with discs, muscles, or nerve roots.