A medial branch block (MBB) is a minimally invasive injection of a local anesthetic near specific nerves to locate and confirm the source of chronic back or neck pain. The primary purpose of the MBB is diagnostic, acting as a temporary test to determine if a patient’s pain originates from the small joints of the spine. A successful block provides temporary relief, which allows a physician to identify the precise anatomical structure causing the discomfort.
Targeting Facet Joint Pain
The pain investigated by an MBB often arises from the facet joints, which are small pairs of joints located between the vertebrae. These joints, also known as zygapophyseal joints, function like hinges, providing stability and guiding the spine’s movements, such as bending and twisting. Degeneration or injury to the cartilage within these joints can lead to inflammation and chronic pain.
The facet joints are innervated by tiny sensory nerves called the medial branch nerves. These nerves do not control muscle movement or skin sensation in the limbs; their sole function is to carry pain signals from the facet joints to the spinal cord and then to the brain. Because the symptoms of facet joint pain can mimic other conditions, identifying the painful joint on an imaging scan is often not enough to confirm the pain source.
The medial branch block targets these specific nerves, temporarily interrupting the transmission of pain signals. By numbing the medial branch nerves with a local anesthetic, the procedure can effectively shut off the pain message originating from the associated facet joint. If the patient experiences significant pain relief immediately following the injection, it confirms that the facet joint is the true source of their chronic discomfort.
Steps of the Injection Procedure
The medial branch block is an outpatient procedure performed under sterile conditions. The patient is positioned lying on their stomach, and the skin over the target area is cleaned with an antiseptic solution. Before the main injection, a small amount of local anesthetic is used to numb the skin, which may cause a brief stinging sensation.
The physician uses real-time X-ray guidance, called fluoroscopy, to precisely visualize the spinal anatomy and guide the injection needle. This imaging technique, often involving a specialized C-arm machine, allows the doctor to watch the needle tip as it is carefully advanced. Accurate needle placement is paramount because the medial branch nerves are very small and lie in a specific groove along the bony structures of the spine.
Using the fluoroscopic guidance, the needle is directed to the bony junction where the medial branch nerve crosses, such as the area where the transverse process meets the superior articular process. Once the needle is confirmed to be in the correct position, a small volume of local anesthetic, such as lidocaine or bupivacaine, is injected near the nerve. This local anesthetic is the substance that temporarily blocks the pain signals.
The entire injection process for a single level usually takes only a few minutes, though multiple levels are often targeted during one session. After the injection, the patient is monitored for a short period to ensure there are no immediate adverse reactions. Patients are asked to record their pain levels and any relief experienced in the hours immediately following the procedure, as this data is crucial for interpreting the results.
Interpreting the Results
The medial branch block is a diagnostic test, not a long-term treatment. Pain relief is expected to be temporary, lasting only as long as the local anesthetic remains active, typically a few hours to a day. The physician evaluates the patient’s report of pain reduction, which is recorded as a percentage compared to the pain felt before the block.
A positive result is defined as a significant reduction in pain, often 50% or more, immediately after the injection. This successful numbing confirms that the facet joint is the primary generator of the patient’s chronic pain. To increase diagnostic certainty and rule out a placebo effect, the procedure is frequently repeated using a different local anesthetic.
If two separate medial branch blocks yield a positive result, the patient is considered a suitable candidate for Radiofrequency Ablation (RFA). RFA is a treatment that uses heat generated by radio waves to create a controlled lesion on the medial branch nerve, stopping pain signals for a much longer period. The successful diagnostic block confirms the exact nerves that need to be targeted for the RFA procedure. The temporary relief from the block is a prediction of the potential long-term success of RFA, which can provide pain relief lasting between six months and over a year.