Basivertebral Nerve Ablation

Anatomy and Physiology

Chronic axial LBP remains a global healthcare problem affecting 30 million people in the United States and costing the healthcare system 90 billion dollars yearly.[16][17] With such a high financial burden, clinicians and researchers need to understand pathoanatomical considerations and the phenotypical profile in chronic axial LBP associated with vertebral endplate damage to target this source and optimize treatment options and success rates. 

The sinuvertebral nerve arises from the ventral ramus of the spinal nerves bilaterally and takes a recurrent course to enter the spinal canal traveling towards the posterior aspect of the vertebra and entering the vertebral body through the basivertebral foramen. This foramen is located midline in the posterior vertebral body and is the entry point for the neurovascular bundle consistent with the BVN and the basivertebral vascular plexus. Although there is anatomical variability within its course, the nerve travels anteriorly into the vertebral body about 30% to 50%, where it forms a trunk cluster of fibers that migrate cranially and caudally towards the vertebral endplates responsible for supplying nociceptive input from damaged vertebral endplates. This branching point is the anatomical site (Figure 1) targeted for the ablative procedure.[2][3][18]

Vertebral endplates are the superior and inferior edge of the vertebral body, and these structures are highly susceptible to injury, post-traumatic degeneration, fissuring, intraosseous edema, and inflammation, which are visible phenotypic markers of vertebral pain noted on magnetic resonance images (MRI) classified as vertebral endplate Modic changes.[5][19][20][21] 

There are three types of Modic changes (MCs), type 1, type 2, and type 3 and these differ based on MRI findings (Figure 2). Type 1 MCs represent vertebral endplate disruption, fissuring, degeneration, active inflammatory vertebral endplate changes and manifest as hypodense or decreased signal intensity of fibrovascular intraosseous bone marrow edema on T1-weighted MRI sequence and as hyperintense or increase signal intensity on T2-weighted MRI sequence. Type 2 MCs represent fatty bone marrow infiltration/replacement of subacute or chronic nature and show an increased signal intensity in both T1 and T2 MRI sequence images. Type 3 MCs are described as decreased intensity in both T1 and T2 MRI sequences.[14][20][22][23]

Although MCs are a radiological finding on MRI, the association of these findings in addition to a history and exam compatible with axial LBP symptoms has been reported by numerous clinical and basic science studies suggesting a positive association for a specific vertebral etiology (vetebrogenic pain). Nociceptive input from these damaged vertebral endplates carried by the BVN is directly related to inflammatory cytokines, substance P, and calcitonin gene-related peptide (CGRP), histologically confirmed with protein gene product (PGP) 9.5 positive staining under microscopy supporting this hypothesis. In particular, type 1 MCs have been reported to have a stronger direct association with more debilitating, severe LBP of longer duration, greater frequency, and worse functional impairments than those subjects with chronic axial LBP but without MCs, hence the great need to focus on a treatment intervention directly targeting this pain generator, such as ablation of the BVN.[4][6][9][20][22][23]

Indications

Clinical studies published to date on BVN ablation utilized a similar patient population, including patients with chronic axial LBP greater than 6 months of duration that has been refractory to non-operative treatment for at least 6 months, in addition to the confirmed presence of MCs type 1 or type 2 on MRI in at least one vertebral endplate, at one or more levels from the L3 to S1 region. Some studies excluded subjects with a history of spinal surgery, spinal stenosis, and use of opioids, while other studies included these, allowing for a more generalizable patient population more similar to daily clinical practice.[24][25][26]

Additional requirements when selecting patients for BVN ablation include documented evidence of significant impairments in function, debilitating pain unresponsive to conservative care, confirmed skeletal maturity on diagnostic imaging, and a history and physical exam supporting other potential primary sources of pain have been ruled out, and vertebral pain is likely. The Food and Drug Administration (FDA) cleared the procedure in 2016 for patients that meet the above criteria.[27][28][29][30]

Contraindications

Contraindications to BVN ablation are generally similar to other interventional spine procedures, such as systemic infections, spinal infections, pregnancy, incomplete skeletal maturity, implantable pulse generators (pacemakers, defibrillators), patients with severe cardiopulmonary compromise, patients where the targeted ablation zone is < 10 mm away from a sensitive structure not intended to be ablated, including the vertebral foramen (spinal canal), and in situations where unintended tissue damage may result based on the clinical assessment of the physician such as spine surgery at the treatment level where existing hardware is within the zone of the BVN ablation.[31][27][24][25]

Additional considerations reported in the literature as an exclusion among published studies included morbid obesity (due to potential tool length limitations in accessing target with elevated levels of adipose tissue in the lumbar region), patients where symptomatic spinal stenosis or radicular pain is the primary pain source, and situations where injury may result from the procedure based on physician assessment such as osteoporosis (particularly in patients with a prior vertebral compression fracture and/or who are actively taking hormonal therapy), in patients with metastatic disease or local malignancy, and in patients with risk for bleeding such as those diagnosed with thrombocytopenia or coagulopathy disorders.[26][28][29][30][32][33][34][35]

Equipment

Safe and accurate targeting of the BVN is critical to the success of the ablation procedure. The procedure is performed by a pain physician, spine surgeon, or interventional radiologist with experience in image-guided spinal procedures, preferably with C-arm fluoroscopy or computerized tomography (CT) guidance. A combination of anterior-posterior (AP), lateral, and oblique C-arm fluoroscopic views are utilized to localize the pedicle and to guide the positioning of instruments. A single C-arm is most often used. However, two C-arms may be used, one for lateral and one for AP and oblique images.

In addition to a CT or fluoroscopy imaging, equipment for BVN ablation includes: an introducer diamond or bevel tipped trocar to access the vertebral body through a transpedicular approach; a curved cannula assembly with accompanying straight stylet to create a channel in the vertebral body to the BVN terminus (target site), and a bipolar radiofrequency ablation probe and radiofrequency generator to create the ablative lesion in the nerve terminus (see technique section below for details). Additional supplies include standardized surgical sterile supplies, such as sterile gowns, gloves, sterile hats, shoe covers, masks, appropriate drapes, sponges, laps, and other supplies to minimize risks of infection.

Personnel

An experienced clinician must perform the procedure. In addition to the clinician performing the procedure, intraoperative personnel includes a fluoroscopy technologist (radiology technician), scrub technician, circulating nurse, and an anesthesiologist or nurse anesthetist for appropriate sedation to keep the patient comfortable safe, and monitored.

Preparation

In addition to a detailed medical history and physical examination to support the etiology of vertebral pain as the source of the patient's chronic axial LBP, the physician must document radiological evidence of type 1 or type 2 Modic changes on MRI and complete treatment history to support the rationale behind the procedure, including longstanding debilitating LBP with functional impairments greater than 6 months unresponsive to at least 6 months of conservative care.

The BVN ablation procedure utilizes a similar transpedicular approach to the vertebral augmentation procedure. Although there is no consensus on perioperative management before BVN ablation, it is reasonable to follow a similar standard of care to other percutaneous spinal interventions. In preparation for the procedure, the following should be obtained: complete metabolic profile (CMP), complete blood count (CBC), and a coagulative profile to assess bleeding risk and rule out underlying infection, severe thrombocytopenia, anemia, or metabolic disorders.

It is also highly recommended to follow guidelines on blood transfusion, discontinuation of anticoagulation, which are variable based on the anticoagulant in question, and perioperative intravenous (IV) antibiotics, such as 2 grams of cefazolin (or 600 mg clindamycin if penicillin allergy) 60 minutes pre-procedure, as a prophylactic measure standard of care to interventional spinal procedures. Based on the patient's comorbidities and physician's judgment, the procedure may be performed under general and monitored anesthesia care (MAC) sedation.

Technique or Treatment

BVN ablation is performed in an outpatient setting by properly trained physicians and surgeons. This procedure has technical similarities with vertebra augmentation as it uses a transpedicular approach, although an extrapedicular approach has been described, and with lumbar radiofrequency ablation, as it uses an ablative lesion to the BVN to interrupt nociceptive signaling from damaged vertebral endplates. The first step in this procedure is to position the patient in a prone position under general anesthesia or MAC with continuous cardiac monitoring, pulse oximetry, and blood pressure. Second, utilizing a standardized sterile technique, the patient is prepped, and the target level and location of entry are marked and confirmed with C-arm fluoroscopy or CT guidance. Obtaining perfect image guidance is essential for this procedure, so the first step should be to rotate the C-arm to obtain a true anterior-posterior (AP) view of the pedicles at the level of entry to optimize a transpedicular approach.

The skin entry point and angle are marked with a sterile marker, and the skin is anesthetized with 1% lidocaine anesthetic, and a small incision is made with a scalpel. Next, a 22-gauge spinal needle may be used at the target entry position to anesthetize the pathway towards the periosteum. An introducer trocar is placed along the same trajectory and advanced through the pedicle, starting at the superior lateral aspect until it passes the posterior vertebral body wall. It is important to maintain a trajectory superior to the inferior cortex and lateral to the medial cortex of the pedicle to prevent trocar entry into the spinal canal or near neural elements. As the trocar is slowly advanced using a mallet, multiple AP and lateral C-arm views are obtained to ensure a safe trajectory.

Once the vertebra body is breached, the trocar is removed from the introducer cannula, and a curved cannula assembly (curved cannula and curved stylet) is that facilitates the creation of a curved channel toward the target site at the BVN terminus found midline, approximately 30% to 50% across the vertebral body width from posterior to anterior (Figure 3). Once the target site is confirmed with AP and lateral C-arm views, the curved stylet is removed, and a bipolar radiofrequency probe is inserted. The probe is connected to a radiofrequency generator, and radiofrequency energy is used to create approximately a 1 cm spherical lesion (85 degrees C for 15 minutes) at the BVN terminus. Upon completion, the radiofrequency probe and the introducer cannula are removed, and the subcutaneous tissue and skin are closed in a standard sterile fashion with a pressure dressing and skin glue or steri-strips. Sutures or staples are usually not necessary.   

Patients are transferred to a post-anesthesia care unit (PACU) for monitoring.  Vital signs and neurological function are reassessed after the procedure. Patients should be discharged the same day. Post-discharge, patients should be instructed to monitor the surgical site and be educated on signs of infection, activity restrictions (no lifting greater than 15 lbs, twisting, bending of the spine), and to not submerge themselves in water for at least 48 hours after the procedure. Follow-up post-procedure visits and full return to activity are based on each clinician's discretion.

Complications

The procedure is considered generally safe, with a very low rate of adverse events (AEs) reported among all clinical studies, totaling 473 procedures. Temporary exacerbation in LBP symptoms and incisional pain were the most commonly reported self-limiting AEs post-procedure. Additional minor AEs reported include transient radiculitis, which resolved after oral medication, and rare instances of non-permanent lumbar/sacral radiculopathy, nerve root injury, and motor/sensory deficits.

Serious AEs reported in the 473 clinical procedures included one case of a vertebral compression fracture in a sham crossover-procedure patient taking hormonal therapy, and in commercially treated patients, there have been two serious adverse events that were device-procedure related, one case of retroperitoneal hemorrhage, and one case of vertebral compression fracture. There have been no reports of thermal injuries, spinal cord injury, avascular necrosis, and post-procedure infections were documented. Among the AEs reported in the clinical studies that were device-procedure related, the median time to resolution was 66.5 days postoperatively.[32][33][34][35]

Clinical Significance

The cumulative data among multiple studies on BVN ablation demonstrated consistent, reproducible, clinically meaningful, and statistically significant improvement in reducing pain and improving function in patients with diagnostic evidence of vertebral pain. Among 11 clinical studies with direct patient data, 3 reviews, 2 clinical guidelines, and 1 systematic review published to date, there is a consensus that the procedure is effective at short-term and perhaps long-term in patients that meet the above-described indications.[24][25][26]

Documented improvements in pain reduction measured by the visual analog scale, functional disability measured by the Oswestry disability index, opioid utilization reduction, and improved quality of life measured by the short-form 36 and EQ-5D-5L have been reported. In fact, studies have pointed out that there is evidence that BVN ablation is more beneficial than the current standard of care for the treatment of low back pain from damaged vertebral endplates.[28][29][30]

The current literature with level Ia-IV studies consistently exhibits positive outcomes with a minimal clinically important difference in reducing pain and improving function, and based upon the available present data, society guidelines strongly recommend BVN ablation in a subset of patients with chronic axial LBP, particularly those with pain greater than 6 months of duration, unresponsive to conservative treatment for at least 6 months, and with diagnostic evidence of vertebral endplate damage (MCs) suggesting a vertebrogenic etiology.[32][33][34][35]

Enhancing Healthcare Team Outcomes

Interprofessional team multidisciplinary collaboration is essential for optimal outcomes in low back pain treatment, and a risk/benefit analysis should always be completed before proceeding with this intervention, as any other spinal procedure, the standard of care should always be followed with conservative methods first, and a treatment plan embracing shared decision making between the patient and the health care team. Clinicians are responsible for proper diagnosis, perioperative assessment, surgical intervention, and postoperative follow-up.

In addition, in this interprofessional model, clinicians act as guides to patients along the healthcare continuum of the low back pain treatment algorithm. Nursing facilitates coordination of activities among therapists and other consultants that help patients achieve their maximum clinical improvement after the intervention and alongside the device representative and the physician educating patients on the expected pre and post-intervention course. This interprofessional, multidisciplinary model will lead to the optimization of patient outcomes. [Level 5]