Overview of Ablative Nerve Block
An ablative nerve block is a simple procedure that uses high-frequency waves (300 to 500 Hz) to stop pain signals in the nerves. It’s like turning off a switch that carries the pain message to your brain. This method was first used in 1975 to help treat chronic back pain and a certain type of leg pain known as sciatica, when the cause of these conditions couldn’t be explained. Previously, the treatment was to cut a nerve in the back known as the dorsal rami via the intertransverse ligaments.
Nowadays, the most common use of nerve ablation is to target the medial branches of the dorsal rami, nerves associated with chronic back pain. This procedure is often used to help people with persistent low back pain. Most people feel the biggest improvement within the first month after the procedure, but the relief from pain can last up to a year in some cases.
However, not all studies show that it works better than a placebo, which means some people might feel better just because they believe the treatment works. That said, recent medical guidelines do support the use of ablative nerve blocks to a moderate extent. There is also evidence supporting its use for chronic discogenic back pain, which originates from damaged spinal discs. The technique might also be beneficial when other treatments aren’t helping, especially if temporary blocks using short-acting anesthesia provide relief.
Beyond back pain, ablative nerve blocks can also be used to treat pain from knee joint osteoarthritis, a facial pain condition called trigeminal neuralgia, and chronic pain syndromes in the abdomen and chest. As this procedure is most often used for back pain treatment, most of the following discussion will focus on this particular use, while also mentioning its applications in treating other conditions.
Anatomy and Physiology of Ablative Nerve Block
Facet-mediated pain is a type of discomfort caused by a condition called facet arthropathy or arthritis. This condition can develop as part of the natural wear and tear on the spine over time. Each facet joint involved in this condition is made up of the lower connecting point of one vertebra (a bone in the spine) and the upper connecting point of the vertebra directly below it. These joints can cause pain when they are affected by arthritis.
The source of feeling in these joints is provided by nerve branches from the main nerves that leave the spine at the same level and the level above. For example, the joint between the fourth and fifth lumbar vertebrae in your lower back (L4-L5) gets its sensation from nerve branches of the third and fourth lumbar nerve roots, located on the fourth and fifth vertebrae, respectively. The nerve branches typically run over the base of the bone extensions at their junctions with the upper connecting points. The L5 nerve branch is usually found in a groove at the base of the first sacral (S1) upper connecting point (a bone in your lower spine). The branch of the nerve providing sensation to the facet joint originates from this location.
In most cases, the nerves that supply sensation to the joints between the fourth and fifth lumbar vertebrae (L4-L5) and fifth lumbar and first sacral (L5-S1) vertebrae are the ones most commonly chosen for a treatment called radiofrequency ablation. During this procedure, an electrode with an uncovered tip is pushed towards the concave area formed between the upper connecting point and the adjacent bone extension, which is close to the nerve suspected of causing the pain. High-frequency energy is produced at this location to cause targeted damage via coagulation, disrupting pain signals. This procedure is usually performed under X-Ray guidance. In the field of pain medicine, radiofrequency ablation primarily targets the specific nerves that supply the pain-causing facet joints. Further studies are still ongoing to find out how effective this treatment can be for other common causes of pain.
Radiofrequency ablation works by blocking pain signals from heading from the periphery of the body to the central nervous system, while preserving motor and sensory nerve function. It’s believed that this works by modifying the pain signals. It is not just through heating and destroying the nerve, but also by blocking the release of certain inflammatory substances called cytokines, which are part of the immune system’s response to injuries.
Why do People Need Ablative Nerve Block
Nerve ablation is a treatment used to help with severe pain in the back of the neck and lower back that hasn’t improved through other treatments. This procedure can also help with chronic neck pain caused by whiplash, and with persistent headaches due to the irritation of nerves in the back of the head and face. Nerve ablation involves applying an anesthetic to the suspected problem-causing nerve to ease the pain.
Researchers are examining whether nerve ablation can aid in relieving pain from the nerves outside of the spine. They are specifically focusing on knee osteoarthritis and a foot condition called plantar fasciitis. Studies have found that when an ablation technique using cold temperature, known as cooled radiofrequency ablation, is used on the genicular nerve (knee nerves), it effectively relieves persistent knee pain caused by osteoarthritis. Moreover, studies have found an improvement in knee function for up to 6 months following the ablation procedure.
It should be noted that there are no specific signs or symptoms that clearly indicate the need for nerve ablation. However, pain from lumbar facet joints, joints in the lower back, tends to be centered in the area along the spine and may be referred to as pain in the back of the thighs. It is exceptionally rare for this pain to extend below the knees. Medical practitioners often use a procedure called medial branch blocks, which involves numbing nerves with local anesthesia, to determine if radiofrequency ablation would be successful. Those who respond positively to medial branch blocks tend to have reduced lower back pain and improved functioning.
When a Person Should Avoid Ablative Nerve Block
Ablative nerve block, a procedure to help reduce pain by interrupting pain signals in certain nerves, may not be suitable for everyone. Certain conditions can make this procedure unsafe. These conditions include:
- Having an active local infection at the point where the needle is to be inserted.
- Having a systemic infection, which is an infection throughout the body.
- Being allergic to the local anesthesia (medicine to numb the area).
- Having high pressure inside the skull (also known as elevated intracranial pressure).
Patients who are on blood-thinning medicines (anticoagulants) also pose a challenge for this procedure. The American guidelines recommend that the patient stop taking the following medicines some days before the procedure to reduce the risk of excess bleeding:
- Aspirin – stop 6 days beforehand
- Clopidogrel – stop 7 days beforehand
- Apixaban – stop 3 to 5 days beforehand
- Rivaroxaban – stop 3 days beforehand
- Warfarin – stop 5 days beforehand
- Intravenous Heparin (given via a vein) – stop 4 hours beforehand
Other conditions that can make the procedure less effective or riskier include:
- Existing neurological issues
- Worrying medical results or scan findings
- Identified causes of low back pain, such as a herniated disc, slipped vertebrae, arthritis of the spine, narrowing of the spinal canal, cancer, infection or injury
- Prior nerve block procedures that did not alleviate pain
Additionally, certain physical changes or problems in the patient’s body could make it difficult for the procedure to be performed successfully. Some technical challenges include:
- Scoliosis or curvature of the spine
- Severe degenerative changes or damage due to aging
- Facet arthropathy or arthritis in specific parts of the spine
- Bone spurs or bony projections along the edges of bones
Bipolar radiofrequency ablation, a type of ablative nerve block, can be used in patients with implanted devices such as heart or deep brain stimulators. However, it’s important to turn off the deep brain stimulator during the procedure and to keep the surgical tools as far from these devices as possible to avoid interference.
Equipment used for Ablative Nerve Block
The procedure is usually done in a clean special procedure room, with the patient lying face down on the examination table.
Here are some crucial supplies for the procedure (see Image. Standard Nerve Block Tray [PENG Block]):
- A C-arm mobile fluoroscopic unit, which is a device that uses X-rays to produce real-time images of the body.
- Local anesthetic medication that numbs the area where the procedure will take place.
- A continuous high-frequency radiofrequency generator with inbuilt monitors for temperature, resistance, voltage, and electric current. This device produces heat to block the pain signals from the nerves.
- Introductory Quincke needles, which are used to insert the local anesthetic medication. These needles vary in size but are typically 50 to 150mm long and have a diameter of 22- or 25-gauge for blocking one nerve.
- Radiofrequency cannulas which are tubes often inserted with the needles that have corresponding electrodes (18-gauge or larger is recommended to increase the success rate). These are used to located the nerve to be blocked.
- Active and ground electrodes which produce and regulate the high-frequency current used to block the pain signals.
Before the procedure, all equipment is checked to make sure it’s in good working condition.
Who is needed to perform Ablative Nerve Block?
Like any procedure that targets the spine, radiofrequency ablation should be performed by a doctor who is specially trained in procedures guided by fluoroscopy. Fluoroscopy is a type of medical imaging that shows a continuous X-ray image on a monitor, almost like an X-ray movie. The doctors who can conduct this procedure have went through special schooling in fields like anesthesiology (which deals with pain relief), physiatry (which deals with physical medicine and rehabilitation), neurology (which deals with disorders of the nervous system), psychiatry (which deals with mental illnesses), or neurosurgery (which is the surgical specialization focused on the nervous system).
After the residency, these doctors usually take extra training in pain management or spine issues. This specialized training is done under a seasoned expert before the doctor does the procedure on their own. During the radiofrequency ablation procedure, other members of the medical team are present to help. One person will prepare the needed medication and operate the machine that generates the radiofrequency waves. Another skilled professional, the radiology technician, will work the C-arm — the machine that takes the X-ray images — under the doctor’s instruction.
A nurse is also there throughout the procedure to constantly monitor the patient’s vital signs like heart rate and blood pressure, and to keep a record of the blood pressure every 5 minutes. The nurse is also prepared to give intravenous (IV) fluids and conscious sedation if needed. Conscious sedation is when medication is used to help the patient relax or sleep during the procedure. Another one of the nurse’s roles during the ablation is to frequently check the grounding pads. These are pads that help manage the flow of electricity during the procedure. It’s important that they stick fully to the skin and that the skin and pads don’t get too hot, to avoid any burns.
Preparing for Ablative Nerve Block
Before a procedure that uses radio waves to destroy tissue can be done, there needs to be a successful use of anesthetic to numb the nerve that’s being targeted. This step is a must-have to locate the right nerve. During this procedure, the patient should not be too sedated. This means they won’t feel drowsy or relaxed from the medicines. It’s important that the patient can describe what they are feeling during the procedure. This helps the doctor accurately destroy or damage the target nerve.
How is Ablative Nerve Block performed
The procedure described here is known as a Lumbar Medial Branch Block and Lumbar Radiofrequency Ablation. Let’s break down these steps into simpler terms:
First, the doctor positions you comfortably and ensures the area of your back where the procedure will happen is well exposed. The skin is cleaned and prepared. The doctor then uses a tool called a fluoroscope, which acts like an X-ray movie, to spot the exact area for the procedure. For your comfort, a small amount of local anesthetic is applied at the point where the needle will enter your skin.
In a Lumbar Medial Branch Block, the doctor uses a specific kind of needle called a spinal needle. This needle is directed carefully towards different nerves in your lower back. The doctors use the fluoroscope to ensure the placement of the needle is accurate, and that it isn’t inside a blood vessel. Once they’ve checked everything is okay, they inject a local anesthetic.
In Lumbar Radiofrequency Ablation, the doctors use a similar approach. A tube-like structure called an introducer cannula is carefully pushed through your skin and towards the same nerves targeted in the previous procedure. This is done using fluoroscopic guidance. The cannula is positioned almost parallel to the nerve to maximize coagulation, which means to thicken and help to stop potential bleeding.
Once the needle is correctly placed, an active electrode is passed through it. The doctor finds the target location by applying sensory stimulation, recreating the painful symptoms that you would usually feel. This is then followed by motor stimulation to ensure the active tip is not too close to nerves that control movement. Then, a local anesthetic agent is applied.
Finally, a device known as a generator creates a continuous output voltage which is applied at the tip of the electrode. This generator is kept at a temperature of 70 to 80°C for about one minute, creating a zone of thermally induced coagulation, essentially using heat to treat the area.
Possible Complications of Ablative Nerve Block
Nerve ablation is a simple type of surgery that carries a low risk and doesn’t usually cause many negative side effects. Still, like any other medical procedure, there are a few common problems that might happen.
When the doctor inserts (or advances) the needle used for the procedure, a handful of things might occur. You could experience swelling and pain in the area, even though this pain usually fades quickly. In some cases, you might also see a bruise, known as a hematoma, which happens when blood collects outside of blood vessels. In rare cases, the doctor may accidentally puncture the coverings of the brain and spinal cord (dura), leading to a condition called pneumothorax, which is when air collects between the lung and the chest wall causing the lung to collapse. This can also result in spinal cord injuries or infection (like meningitis or an abscess) in rare cases. Temporary weakness or numbness may also occur, as well as an allergic reaction to the tools or anesthetics used.
During radiofrequency ablation, which is a specific type of nerve ablation, some people may experience weakness in their lower back muscles or abnormal sensations like tingling or numbness (dysesthesias). Some patients liken this to a mild sunburn (neuritis). Others might have burns if the ground pad used in the procedure isn’t placed correctly. Pain might get worse for some, or they may lose some sensation. Some people might experience new nerve related pain, muscle shrinking (atrophy) due to loss of nerve supply, flushing, low blood pressure, headaches not related to position, heightened sensitivity to touch (allodynia) in the skin around the spine or in the outlets of the spine, or an abnormal forward bending posture (camptocormia).
If ablation is done on the cluster of nerves in the brain (trigeminal ganglion), the side effects might include facial numbness, abnormal sensations, painful sensations in an area that’s numbed (anesthesia dolorosa), numbness in the cornea of the eye (corneal anesthesia), inflammation of the cornea (keratitis), or trouble controlling facial muscles (trigeminal motor dysfunction).
What Else Should I Know About Ablative Nerve Block?
An estimated hundred million Americans deal with some type of recurring pain, which adds up to over $100 billion in costs every year. Additionally, it’s reported that 84% of adults in the United States face chronic low-back pain at some point in their lives. The root cause of this pain can involve various factors. Among them, the most commonly seen is the destruction of the cushion-like cartilage in our spine’s facet joints. This can result in significant discomfort when the spine is stretched or twisted.
The sensory nerves associated with this discomfort are often targeted in processes that aim to destruct or ‘ablate’ the nerves. A common technique is radiofrequency ablation, which is an effective method to reduce the severity of back pain for lasting periods, anywhere between 6 to 24 months. Destructive nerve blocks are also useful in treating facial and occipital (the back of the head) nerve pain, complications from regional pain syndrome, hip and knee osteoarthritis, and a condition affecting the foot known as plantar fasciitis. Such techniques aim to reduce dependence on potentially habit-forming pain relievers like opioids.
This review is mainly about conventional radiofrequency ablation. It uses a continuous source of energy that results in the death of the targeted tissue through heat. Other forms of ablation used for managing pain include:
1. Pulsed radiofrequency: This applies heat in a rhythmic manner at lower temperatures than conventional radiofrequency to avoid nerve destruction.
2. Cooled radiofrequency: This uses special electrodes cooled with water, allowing high temperatures at the treatment site with less risk of damaging surrounding tissues. This form may be preferred in patients with certain technical limitations.
3. Cryoablation: This destroys nerve fibers by harming their small blood vessels. It’s becoming more popular because it results in less pain after the procedure and less chance of neuroma (a growth or tumor on a nerve) formation when compared to conventional radiofrequency.
Destructive nerve blocks have been successfully used to treat conditions such as intercostal neuralgia (a pain that affects the nerves situated between the ribs) and chronic knee pain. Moreover, studies have shown that these methods are effective for managing pain associated with upper abdominal cancers like stomach or pancreatic cancer, chronic headaches, and spinal compression fractures. More research is required in some fields.
Other conditions where destructive nerve block techniques can be useful for managing pain include facial nerve pain, knee osteoarthritis, head and face pain syndromes, headaches originating in the neck, nerve pain between the ribs, chronic chest pain, chronic shoulder pain, and ongoing testicular pain. Each of these conditions has specific nerves that are targeted for treatment. Remember, the main goal of these treatments is to reduce pain and improve the quality of life.
