Medial Branch Block

For convenience purposes, the spine can be divided into an anterior (front) section and a posterior (back) section, that work together to maintain proper function. The anterior section contains the vertebral bodies and the intervertebral discs and is the primary load-bearing part of the spine. The posterior portion, which contains the zygapophyseal (Z or facet) joints, lamina, and the transverse and spinous processes, controls the motions of the spine and provides for all musculotendonous insertions on the spine. In the lower back, the usual location of injury is the intervertebral disc which is usually injured by bending forward while twisting to pick something up, often with an outstretched arm. The posterior section of the spine accounts for about 20-25% of low back pain and over half of chronic neck pain and can be injured through repeated bending, a hyper-extension (bending back too far) injury such as “whiplash”, or through “wear and tear” of the facet joints, a problem which can happen with age.

The facet joints are small joints in the back of the spine that form a connection between each vertebrae. Each vertebrae is a part of four facet joints, two on the upper or superior surface, and two on the lower or inferior surface. These joints are diarthroidal which means that there are only two surfaces rubbing together, like the hip joint and the finger joints. The inner surface of each joint contains articular cartilage which can be injured though a single, high-velocity injury, or more commonly, slowly be injured over time, a “wear and tear” problem known as osteoarthritis. These joints, as with most joints are surrounded by a soft tissue capsule that holds the fluid in the joint. As the joint capsule becomes swollen from fluid collecting in the joint, which is typical with osteoarthritis, the joint capsule begins to produce discomfort and frequent muscle spasms. As well, the injury to the cartilage in the joint and often the underlying bone also directly produces discomfort. The capsule, cartilage, and facet bone are all innervated from nerves arising from the medial branches of the dorsal rami. These nerves transmit pain upward, through multiple connections, to the brain, causing us to sense pain.

What Is The Purpose Of Medial Branch Blocks?

Medial branch blocks are a purely diagnostic procedure. These injections are normally used to confirm that the pain impulses are traveling through a particular set of medial branch nerves (each Z-joint is innervated by two medial branch nerves). If pain can be eliminated by blocking these nerves, the patient may benefit from radiofrequency ablation of the same nerves to produce a more permanent reduction in pain.

How Are These Injections Administered?

With some of these procedures, you may be asked to stop medications that thin your blood. However, current medical advice for most of these procedures, is that the risk of stopping these medications is worse than the risk of having a bleeding complication from the procedure. If you are on medications that thin your blood, such as aspirin, warfarin, heparin, enoxoparin, ticlopidine, clopidogrel, diabigatran, dipyridamole, prasugrel, or any other blood thinning agents such as anti-inflammatory agents, please let your physician know at least one week prior to the procedure. Do not take your regular pain medications for six hours before or after the procedure. You should continue to take your routine medications (such as high blood pressure and diabetes medications) before the procedure. If you are on antibiotics please notify your physician, he may wait to do the procedure. If you have an active infection or fever we will not do the procedure.

These procedures (with the exception of radiofrequency neurotomy) typically do not require sedation. When receiving IV sedation you should not eat or drink anything (except your routine medications) for four hours prior to the procedure; this again, lowers the chance of having complications. You are expected to have a ride to and from the procedure. The procedure usually takes about fifteen minutes though you may be at the facility for as long as 45min. Once you arrive to the facility, if having sedation, a nurse will place an IV in your arm. After this has been done and the doctor is ready, you will be taken to the room and positioned on the table.

A spinal needle will be advanced to the appropriate location using bones as landmarks. Your physician will use fluoroscopy (a live x-ray) and other technical aids to ensure that the needle is in the right place.

For medial branch blocks, the physician will place the needle adjacent to the nerve based on bony landmarks that can be visualized with the fluoroscopy unit. He will then inject a small amount of contrast to confirm that the needle tip is not in a blood vessel. If the needle is in the appropriate position, he will inject a small amount of solution to “block” the nerve. You will be expected to keep a pain diary following the procedure to record pain each hour and note how long the block lasts. Remember, this is a diagnostic test and not a permanent treatment for pain.

What Are The Risks Of These Procedures?

With any operation or injection procedure there are risks. In the case of these procedures, the risks are small. These procedures are performed on the posterior spine and are thus away from the neuroaxis (spinal cord, etc). This dramatically reduces the risk of serious problems.

With medial branch blocks there are no specific side-effects or complications, only the general ones listed below.


As with any injection through the skin, it is possible for bacteria to gain entry causing an infection. Your physician will use a sterile technique and the risk of infection with these procedures is very small.

Sometimes a patient's blood pressure falls at the time of the injection. If so, the doctor will use the venous canula inserted before the epidural procedure commenced so that intravenous fluids or medication, if necessary, can rapidly control the blood pressure.

How Long Does It Take?

These procedures take 10 minutes to one hour depending on the procedure and number of levels involved. On occasion radiofrequency ablation can take longer if the nerves are difficult to localize. The patient will usually be in the recovery room for 5-10 minutes after the procedure.

Repetitions

Medial branch blocks may be repeated with a different local anesthetic to absolutely confirm that blocking the medial branch nerves will be effective. Repeating this procedure is at the doctor’s discretion.
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IF YOU HAVE ANY QUESTIONS ABOUT THE PROCEDURE OR ANY OF THE INFORMATION YOU HAVE JUST READ, PLEASE ASK THE STAFF OR YOUR DOCTOR.