What Is A Lumbar Medial Branch Block?

A lumbar medial branch block is a diagnostic procedure used to discern the etiology of chronic back pain related to the lumbar area of the spinal column. It involves injection of a local anesthetic near or around the medial branch nerves of the lumbar spine. The nerves exist in pairs on the posterior portion of the spinal column. The only function of these small nerves is to carry pain signals from the area of the facet joint toward the brain. Facet joints are found between the backbones, also known as vertebrae. These joints stabilize and allow for motion in the spine.

Whenever a facet joint is irritated, inflamed, or damaged, it may lead to pain involving the buttocks, abdomen, low back, groin, or lower extremities. If a lumbar medial branch block does not decrease pain levels, the facet joint is most likely not the origin of back pain. If a lumbar medial branch block produces a dramatic decrease in pain levels, the facet joint is most likely the reason for the back pain. Hence, the block is indicated for diagnostic purposes, as opposed to therapeutic purposes, with regard to chronic low back pain.

How Is A Lumbar Medial Branch Block Performed?

A lumbar medial branch block is usually performed at an ambulatory surgical center, which can be freestanding or located within a hospital. After the patient signs informed consent forms, the procedure can go forward. On the day of the procedure, the patient lies in a supine position on a table. The lower back is cleansed with an antiseptic solution. Landmarks are palpated and the injection is marked with a felt tipped surgical pen.

The outlined area of injection is infiltrated with a local anesthetic to provide loss of sensation. Full sedation is not routinely used during a lumbar medial branch block. A thin procedure needle is then inserted and advanced to an area near or around the medial branch nerves. To enhance accuracy of needle placement, the procedure can be done with X-ray guidance. Once needle placement is verified, contrast dye can be injected to ensure that the anesthetic will flood the correct area near or around the nerves. Once proper direction of flow is established with the contrast dye, the physician slowly injects an anesthetic and removes the needle.

Multiple levels of the lumbar spine can be injected using this technique. Some physicians mix the local anesthetic with a corticosteroid such as dexamethasone or betamethasone to prolong the action of the local anesthetic. Most patients report immediate relief of pain. If this is the case, facet joint disease is indeed the culprit. Any pain relief attributed to the injection is short-lived, and for this reason the patient will be referred for another procedure termed radiofrequency ablation (RFA). This procedure has the possibility to provide sustained pain relief in the case of back pain secondary to disease of the facet joints.

A lumbar medial branch block can be administered in 15 to 30 minutes. The procedure can be performed in the ambulatory surgery wing of a hospital or clinic. The vital signs and pain scores of the patient are monitored for at least 30 minutes post injection in a recovery area. Following the recovery from the procedure, the patient has to be transported home by another adult. Activity should be restricted for the balance of the day. Patients in the following situations should not receive a lumbar medial branch block:

  • Active infection
  • Treatment with a blood thinner
  • Allergies to any of the medications being injected

A lumbar medial branch block is a low risk procedure. The following complications, though rare, may be encountered:

  • Tenderness at the site of injection
  • Infection
  • Worsening of pain symptoms
  • Allergic reaction to medication injected
  • High blood sugar, if a steroid is used
  • Kidney failure
  • Nerve damage
  • Anesthetic toxicity
  • Bleeding
  • Headaches
  • Dysfunction of the bowel or bladder
  • Sexual dysfunction
  • Paralysis
  • Intravascular injection of local anesthetis

Conditions Related To Lumbar Medial Branch Blocks

A lumbar medial branch block may be diagnostic in patients with the following diagnoses of the lumbar spine:

Most patients who receive lumbar medial branch blocks have failed more conservative therapy including anti-inflammatories, analgesics, opioids, gabapentin, physical therapy (PT), or chiropractic manipulation.


Lumbar medial branch blocks can be used to diagnose persistent low back pain secondary to disease of the facet joints. Medial branch nerves carry pain information from the spinal column to the brain. A lumbar medial branch block has the potential to pinpoint the exact facet joint that is transmitting pain signals.

Patients with a favorable response to the block should give serious consideration to a therapeutic procedure called radiofrequency ablation (RFA).  It involves disruption of pain transmission by the medial branch nerves using a special heat probe. The procedure can provide pain relief anywhere from six months to one year. Both lumbar medial branch block and RFA are relatively safe.


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