Ablative Nerve Block

Anatomy and Physiology

Facet-mediated pain is caused by facet arthropathy or arthritis, which arises during the degenerative process of the spinal column. A single facet joint comprises the inferior articulating process of 1 vertebra and the superior articulating process of the vertebra directly inferior. These joints, also known as zygapophyseal joints, are synovial and are potential generators of pain (see Image. Facet Joint).

Medial branches from the primary dorsal rami of spinal nerve roots at the same level and 1 level above provide sensory innervation to the facet (for example, the L4-L5 facet joint is innervated by the medial branches of L3 and L4, located on L4 and L5 respectively). The medial branches typically course over the bases of the transverse processes at their junctions with the superior articulating processes. The L5 dorsal ramus is usually found inside a groove at the base of the S1 superior articular process. The L5 medial branch originates from this location towards the lower end of the process.

The 2 most typically afflicted lumbar facet joints are L4-L5 and L5-S1, so the nerves that innervate these joints, the L3 and L4 medial branches and the L5 dorsal ramus, are the most frequently chosen for ablation. The L5 dorsal ramus is ablated as it is more accessible than the medial branch.[8]

An insulated electrode with an uninsulated tip is advanced toward the concavity formed between the superior articulating process and the adjacent transverse process, which is in proximity to the nerve suspected of causing the symptoms. This location is where high-frequency or radiofrequency energy is generated to produce a lesion via coagulative necrosis, thereby disrupting afferent pain signals. In pain medicine, radiofrequency ablation most commonly involves targeting the specific medial branches of the dorsal rami that innervate pain-producing facet joints under fluoroscopic guidance. However, further investigations regarding the efficacy of ablation in other common pain syndromes continue to diversify its use.[9][7]

Radioablation blocks nociceptive signals traveling through A-delta and C-fibers from the peripheral to the central nervous system while preserving motor and sensory (A-beta) fibers. The hypothesized mechanism of action is the modulation of pain signals, suppressing the release of immune-mediator cells and pro-inflammatory cytokines (interleukin-1β and interleukin-6) rather than the thermal destruction of the nerve.[10][11]

Indications

Nerve ablation is indicated to treat facet-mediated axial back pain of the cervical and lumbar spine that has failed conservative therapy. Ablation has other uses, such as relief of chronic neck pain after whiplash and chronic headache syndromes due to occipital and trigeminal neuralgia. Ablation is performed after successful analgesia of the suspected trouble-causing nerve with a local anesthetic.

Studies continue to investigate the role of ablation in peripheral nerve-mediated pain outside of the spinal column, particularly in knee osteoarthritis and plantar fasciitis.[12][13] Ablative nerve blocks, with cooled radiofrequency ablation of the genicular nerve, are an effective pain reliever for refractory osteoarthritis of the knee. Furthermore, studies show improved knee function up to 6 months following the ablation procedure.[14]

There are no pathognomonic findings on history or physical examination.[15] However, pain from lumbar facet joints tends to be nonradicular, centered in the paraspinal regions and may be referred to the posterior thighs in a nondermatomal pattern. Referred pain below the knee joints is very rare.[8] Medial branch blocks, performed with local anesthesia, help determine the likelihood of success of radiofrequency ablation of dorsal primary rami. Patients who respond to the medial branch block are found to have reduced low back pain and increased function.[16][17]

Contraindications

Absolute contraindications for ablative nerve blocks include active local infection at the needle insertion site, systemic infection, allergy to local anesthetic, and elevated intracranial pressure. Patients taking anticoagulants provide a unique challenge for practitioners. Clinical judgment must be followed along with adherence to accepted guidelines. Current guidelines put forth by the American Society of Regional Anesthesia and Pain Medicine (ASRA) recommend that:

• Aspirin to be stopped 6 days preprocedure
• Clopidogrel to be stopped 7 days preprocedure
• Apixaban to be stopped 3 to 5 days preprocedure
• Rivaroxaban to be stopped 3 days preprocedure
• Warfarin to be stopped 5 days preprocedure
• Intravenous heparin to be stopped 4 hours preprocedure

Other relative contraindications that must considered before the procedure include the following:

• Neurologic abnormalities
• Concerning clinical or imaging findings
• Definitive causes of low back pain (eg, disc herniation, spondylolisthesis, spondylosis, spinal stenosis, malignancy, infection, or trauma)
• Lack of pain relief from prior diagnostic nerve blocks [18]

Technical limitations are as follows:

• Scoliosis
• Severe degenerative changes
• Facet arthropathy
• Bone spurs

Bipolar radiofrequency ablation is of use in patients with implantable devices like cardiac implantable electronic devices or deep brain stimulators. The latter is to be switched off during surgery, and the cautery pads must be kept as far away from these implants as possible.[10]

Equipment

The procedure is routinely performed in a sterile procedure suite, with the patient lying prone on a procedure table.

Key supplies for the procedure include the following (see Image. Standard Nerve Block Tray [PENG Block]):

• C-arm mobile fluoroscopic unit                                                                                                                           
• Local anesthetic drug                                                                                                                                       
• Continuous high-frequency radiofrequency generator with a built-in thermocouple, impedance, voltage, and amperage monitor                                 
• Introducer Quincke needles (50 to 150 mm in length, 22- or 25-gauge in diameter for branch block)                                                               
• Radiofrequency cannulas with corresponding electrodes (18-gauge or larger is advisable to increase the capture rate)                                             
• Active and ground electrodes - The active electrode delivers the high-frequency current, which is dissipated through a ground electrode attached to the patient.

All equipment should be checked for proper working order prior to the procedure.

Personnel

As with other interventional spinal procedures, only physicians trained explicitly in fluoroscopically-guided procedures should perform radiofrequency ablation. Qualified physicians typically undergo residency training in anesthesiology, physiatry, neurology, psychiatry, or neurosurgery. This training is followed by an interventional pain or spine fellowship that allows adequate training under an experienced interventionalist before performing the procedure independently. Support staff for the procedure can include an assistant to draw up necessary medications and operate the radiofrequency generator and a radiology technician to operate the C-arm under the guidance of the performing physician.

A nurse should monitor the patient's vital signs continuously during the procedure and record blood pressure at least every 5 minutes throughout the procedure. Nurses should be prepared to administer IV fluids and conscious sedation if indicated as ordered by the physician. During the ablation, nurses are responsible for checking the grounding pads periodically for full adhesion to the skin and for increasing temperature of the skin and pads to avoid burns. 

Preparation

The destruction of tissue via radiofrequency must occur after successful diagnostic anesthetic nerve blocks have located the target nerve. During the procedure, the patient should receive little to no sedation, as they must define what they are experiencing during stimulation and lesioning of the nerve.

Technique or Treatment

The steps of the procedure can be outlined as follows: [8]

The patient is placed in a comfortable position with adequate exposure to the region overlying the target nerve. The skin is cleaned and prepped, and the target is found using fluoroscopy. A small amount of local anesthetic is injected subcutaneously at the point of needle insertion.

Lumbar Medial Branch Block

• The nerves are targeted by advancing the spinal needle under fluoroscopic guidance to the following points as given below:                                               
  • L5 dorsal ramus: The junction of the sacral ala and the sacral articular process
  • L4 medial branch: The junction of the L5 superior articular and transverse processes
  • L3 medial branch: The junction of the L4 superior articular and transverse processes                                       
• Needles are checked for placement into the above junctions and absence of entry into a blood vessel.                   
• Local anesthetic is injected.

Lumbar Radiofrequency Ablation

• The introducer cannula is then inserted through the skin, subcutaneous tissue, and muscle toward the same targets mentioned above, using fluoroscopy to guide the trajectory.                                                           
• This insertion requires a medial and cephalad trajectory to place the cannula almost parallel to the nerve to maximize the coagulation.                           
• Once the needle tip is placed satisfactorily close to the target, the active electrode is inserted through the needle.                                                           
• The target location is found using sensory stimulation, recreating the painful symptoms that the patient experiences.                                                       
• This step is followed by motor stimulation to ensure the active tip is not close to the motor nerves.                               
• Once confirmed, a local anesthetic agent is administered into each cannula. Subsequently, the generator produces a continuous output voltage at the tip of the electrode. The generator should be kept at 70 to 80 °C for approximately 1 minute, creating a zone of thermally induced coagulation.[19]

Complications

Nerve ablation is a minimally invasive, relatively low-risk procedure with a limited adverse event profile.[20] The following is a list of the most commonly associated adverse events.

Complications Associated with the Advancement of the Introducer Needle

• Localized swelling and pain (transient postoperative pain is the premier adverse event)
• Hematoma
• Pneumothorax
• Dural puncture
• Spinal cord trauma
• Subdural injection
• Neural trauma
• Infection (eg, meningitis, abscess)
• Temporary weakness or numbness
• Allergy to materials or anesthetics

Complications Associated with Radiofrequency Ablation [18][21]

• Weakness of lumbar paraspinal muscles
• Dysesthesias
• Transient mild neuritis (may feel like a sunburn)
• Burns (due to errors in ground pad placement)
• Worsened pain
• Sensory loss
• New-onset neuropathic pain
• Atrophy of the multifidus muscle due to denervation
• Flushing
• Hypotension
• Nonpostural headaches
• Allodynia in the paravertebral skin or denervated facets
• Camptocormia [22]

Complications Associated with Intracranial Ablation of the Trigeminal Ganglion

• Facial numbness
• Dysesthesia
• Anesthesia dolorosa
• Corneal anesthesia
• Keratitis
• Trigeminal motor dysfunction

Clinical Significance

One hundred million Americans suffer from some form of chronic pain that results in more than $100 billion in expenses annually. Furthermore, 84% of American adults will suffer from chronic low-back pain at some point in their lifetime. While the causes of low-back pain are often multifactorial and can be due to many causes, the degenerative cascade that affects the spine plays a significant role. Destruction of cartilage that comprises the spinal facet joints results in severe discomfort when placed under stress, typically in extension or rotation of the spine. The sensory nerves responsible are the medial branches of the dorsal rami, the most common target in ablative procedures. Radiofrequency ablation is efficacious in reducing the severity of back pain for extended periods (ranging from 6 to 24 months). Ablative nerve blocks have utility in treating trigeminal and occipital neuralgia, complex regional pain syndrome, hip and knee osteoarthritis, and plantar fasciitis. As with other interventional procedures that provide pain relief, ablation aims to play a significant role in reducing opiates and other habit-forming pain medications.

This review focuses on conventional radiofrequency ablation, which utilizes a continuous energy source causing coagulative thermal necrosis. Other forms of ablation used in pain management include the following:

• Pulsed radiofrequency applies heat in a pulsatile manner (pulse durations of 5 to 50 ms and pulse frequency of 1 to 10 Hz, but the most widely used sequence is a frequency of 2 Hz and a duration of 20 ms) but uses lower temperatures than conventional radiofrequency to avoid neurolysis.                                                           
• Cooled radiofrequency utilizes specialized electrodes cooled with water flowing along its shaft but not at the active tip. This technology allows high temperatures (60 °C) and more spherical lesion sizes to be achieved at the target site with less risk of tissue damage superficial to the target. Cooled radiofrequency may be more useful in patients with technical limitations (mentioned under the contraindications above). Cooled radiofrequency is found to be superior in effectiveness compared to facet joint steroid injections.[23]                                                                                                                                                             
• Cryoablation destroys axons by disrupting the vasa nervorum. It has increased in popularity due to decreased postprocedural hyperalgesia and neuroma formation compared to conventional radiofrequency.

Cases of ablative nerve block use have been successfully used for intercostal neuralgia (see Image. Intercostal Nerve Block Landmark).[24] Ablative nerve blocks of the genicular nerve for chronic new pain have also been shown to be an effective pain reliever for chronic, refractory knee pain.[25] Patients who undergo ablation of the genicular nerve have been shown to have pain for up to 6 months following the procedure.[26] Furthermore, studies have also been done regarding the effectiveness of ablative techniques on cancer pain. Results have shown blocks to be effective for upper abdominal cancers such as gastric or pancreatic cancer.[27] Chronic pericranial headaches have also been studied, and evidence of radiofrequency ablation of the pericranial nerves has been found.[28] One promising 2016 study also looked at radiofrequency ablation in the treatment of vertebral compression fractures. However, more studies need to be done.[29] There is limited effectiveness in using ablative nerve blocks for facet joint osteoarthritis compared to a placebo.[30]

The other conditions in which ablative nerve block is useful in pain management and the corresponding nerves targeted are listed below (see Table. Ablative Nerve Block Indications: Other Conditions).

Table. Ablative Nerve Block Indications: Other Conditions

Enhancing Healthcare Team Outcomes

Patients undergoing ablative nerve blocks for pain management, such as those for back pain, require a coordinated interprofessional approach to ensure safety, minimize risks, and optimize outcomes. Ablative nerve block, commonly performed on an outpatient basis, relies on the collaborative efforts of a dedicated healthcare team to deliver patient-centered care effectively and enhance overall outcomes.

Anesthesiologists, pain management specialists, and surgeons are responsible for performing the actual nerve ablation. To ensure the procedure's success, they must possess the knowledge and skills of ablative techniques, select appropriate candidates, and manage potential complications. Advanced practitioners play a critical role in the preprocedure evaluation, obtaining informed consent, and managing postprocedure care. Patient monitoring is often entrusted to a dedicated nurse or anesthesia provider during the procedure. They are responsible for monitoring the patient's vital signs at regular intervals, managing hypotension, escalating sedation needs, and communicating concerns about the patient's status during the procedure. After the procedure, postanesthesia recovery nurses monitor the patient in the recovery room for several hours. These nurses play a vital role in assessing the patient's recovery from sedation, managing pain, monitoring for complications, and ensuring the patient's readiness for discharge. Before discharge, patients must be thoroughly informed about the possible adverse effects of the procedure, care instructions for the treated area, and clear guidelines on when to seek medical attention postdischarge.[45]

Effective interprofessional communication is key to the success of this collaborative approach. Care coordination is crucial in navigating the patient's journey from assessment through treatment to follow-up, ensuring a seamless transition between different phases of care and enhancing patient safety. By adhering to these principles of skill, strategy, ethics, responsibilities, interprofessional communication, and care coordination, healthcare teams can deliver comprehensive, patient-centered care. This approach improves outcomes for patients undergoing ablative nerve blocks and enhances team performance in managing patients with complex and/or chronic pain.