Rationale for bipolar palisade lesioning
The sacroiliac joint complex receives posterior sensory innervation via the posterior sacral network, which is formed by the lateral branches of the S1–S3 posterior rami, with variable contributions from the S4 lateral branch and the L5 dorsal ramus. Interrupting this network with image-guided percutaneous radiofrequency ablation (RFA) is an established strategy to reduce pain and disability in appropriately selected patients with sacroiliac joint complex pain. Because these posterior sacral nerves traverse a broad and variable course between the posterior sacral foramina and the sacroiliac joint, lesion geometry and coverage are central determinants of procedural success.
A prior systematic review has reported that a substantial proportion of patients undergoing posterior sacral network ablation achieve at least 50% pain relief at six months, with a smaller but notable proportion achieving complete relief over the same interval. However, the wide range of reported outcomes has been attributed in part to heterogeneity in RFA techniques and technologies used to target the sacral lateral branches. Cadaveric work has suggested that bipolar strip lesions along the sacrum can result in substantially higher rates of neural capture compared with conventional monopolar periforaminal RFA, underscoring the importance of lesion continuity and orientation relative to the posterior sacral network.
The bipolar palisade technique is designed to create a continuous strip lesion that spans the typical course of the sacral lateral branches from S1 to S3. In this configuration, electrodes are placed in a craniocaudal line with controlled interelectrode spacing so that sequential bipolar or multipolar lesions coalesce into a linear lesion along the periosteal surface. This approach is conceptually aligned with broader radiofrequency neurotomy principles, where high-grade pain relief depends on thorough destruction of a sufficient length of the targeted nociceptive pathway and on lesion geometry that encompasses anatomic variation in nerve trajectory.
In contrast, conventional monopolar periforaminal techniques may generate smaller, more focal lesions around each active tip. Cadaveric modeling has indicated that the rate of complete neural capture with a conventional periforaminal monopolar technique can be low, which may contribute to variable clinical outcomes. By arranging multiple cannulae in a palisade configuration and using bipolar energy delivery, the operator aims to generate a larger, more contiguous lesion that better matches the three-dimensional distribution of the posterior sacral network. This rationale is further supported by evidence that larger strip lesions, whether created with bipolar or cooled technologies, are more likely to capture the majority of lateral branches when appropriately positioned along the sacrum.
Comparison with conventional periforaminal techniques
Conventional periforaminal sacral RFA techniques typically employ monopolar electrodes positioned adjacent to the posterior sacral foraminal apertures to target the lateral branches as they exit the foramina. In one commonly used approach, a 22-gauge cannula with a 5-mm exposed tip is directed to locations approximately 3–5 mm lateral to the posterior sacral foraminal apertures of S1, S2, and S3, with probe positions defined using an analog clock orientation around each foramen. This strategy focuses lesioning near the foraminal exits but does not necessarily create a continuous lesion along the entire course of the posterior sacral network toward the sacroiliac joint.
Cadaveric work has suggested that conventional periforaminal monopolar RFA may achieve relatively low rates of complete neural capture of the posterior sacral network, with estimates as low as 12.5% in some models. Despite this, clinical studies have demonstrated that periforaminal techniques using conventional monopolar, cooled monopolar, and multi-electrode continuous lesions can yield broadly similar effectiveness when evaluated as technique families. This suggests that while periforaminal approaches can be clinically useful, their capacity to reliably encompass the full variability of sacral lateral branch anatomy may be limited compared with more extensive strip lesion strategies.
The bipolar palisade technique differs fundamentally in its geometric intent. Rather than centering lesions around discrete periforaminal targets, electrodes are aligned along the lateral sacral crest or slightly medial to it, spanning from the first to the third transverse sacral tubercles at S1–S3. When conventional cannulae are used in a multipolar configuration with appropriate spacing, the resulting lesion between electrodes assumes a rounded rectangular shape, and a series of consecutive bipolar or multipolar lesions created in a leapfrogging manner can form a continuous linear strip lesion over the intended target area. This configuration is intended to better capture the posterior innervation of the sacroiliac joint as it traverses from the foramina toward the joint.
From a technical standpoint, periforaminal techniques often rely on multiple cannula passes or specific periforaminal arrangements to increase lesion size when using monopolar RFA. In contrast, bipolar or cooled RFA in a palisade configuration inherently produces larger lesions between closely spaced, parallel cannulae, with recommended inter-cannula spacing on the order of 8–12 mm for conventional cannulae or approximately 10–12 mm in some lateral sacral branch protocols. Although no completed randomized trial directly comparing a bipolar palisade strip lesion to a conventional monopolar periforaminal method has been reported within the available documents, the investigational focus on such comparisons reflects the perceived potential of palisade lesioning to improve neural capture relative to traditional periforaminal strategies.
Procedure steps under fluoroscopic guidance
Standardized performance of sacral palisade RFA begins with patient positioning and imaging. Participants are positioned prone on the procedure table, and cardiopulmonary monitoring is established with continuous vital sign assessment throughout the procedure. The skin over the sacrum is prepped and draped in a sterile fashion using agents such as Betadine or chlorhexidine. Under fluoroscopy, an anteroposterior view with craniocaudal adjustment is obtained to optimize visualization of a crisp, leveled S1 endplate, which serves as a key reference for subsequent needle placement.
After appropriate imaging is obtained, the skin and subcutaneous tissues over the planned entry sites are anesthetized with a small volume of local anesthetic, such as lidocaine. Under direct fluoroscopic guidance, electrode introducers are advanced toward their targets along the sacrum. For the bipolar palisade configuration, electrodes are positioned along the lateral sacral crest, lateral to the inflection points of the S1, S2, and S3 lateral foraminal walls, following the first to third transverse sacral tubercles. A craniocaudal line is maintained, with an interelectrode distance of no more than 15 mm to promote formation of a continuous strip lesion between electrodes.
In some protocols, a monopolar lesion is also created at the L5 dorsal ramus to address its contribution to the posterior sacral network. Cadaveric studies have demonstrated that the L5 dorsal ramus can contribute sensory innervation to the sacroiliac joint by traveling caudally into the posterior sacral network at the level of S1. To control for potential subclinical L5/S1 facet-mediated pain, an electrode may be placed at the junction of the sacral ala and S1 superior articular process to create a monopolar lesion at this site, even when a contiguous bipolar palisade lesion is being formed along the lateral sacral crest.
Once all introducers are in position, correct locations are confirmed in both anteroposterior and lateral fluoroscopic views. The tines of multitined electrodes, where used, are then deployed. Following injection of a small amount of local anesthetic through each cannula to ensure patient comfort, lesions are performed at defined temperature and time parameters—for example, 85°C for 180 seconds at each bipolar site and 80°C for 90 seconds at the monopolar L5 dorsal ramus site in one protocol. After lesioning, the tines are retracted and the electrodes removed. This structured sequence—prone positioning, fluoroscopic alignment, anesthetic infiltration, guided introducer placement, multiplanar confirmation, controlled lesioning, and careful electrode removal—provides a reproducible framework for fluoroscopy-guided palisade RFA on the sacrum.
Technical considerations for complete neural capture
Achieving complete or near-complete capture of the posterior sacral network requires attention to several technical variables, including cannula spacing, parallelism, depth alignment, and the contour of the sacral surface. Conventional RFA cannulae used in a multipolar configuration should generally be placed 8–12 mm apart when using 18- or 20-gauge cannulae with 10–15 mm uninsulated tips, temperatures of 80–90°C, and lesion times of 2–3 minutes, to generate a confluent lesion between electrodes. In lateral sacral branch protocols using bipolar or cooled RFA, cannulae are often placed parallel to each other, spaced approximately 10–12 mm apart and perpendicular to the sacral surface to ensure that the lateral branches are encompassed within a larger strip lesion.
The undulating nature of the dorsal sacral surface, particularly along the lateral sacral crest where sacral tubercles are prominent, can introduce tip offset between electrodes. Tip offset increases the likelihood of generating two discrete monopolar lesions around each tip rather than a continuous bipolar lesion, potentially resulting in incomplete nerve capture. One strategy to minimize tip offset is to move the strip lesions slightly medial to the lateral sacral crest while remaining lateral to the posterior sacral foramina, thereby positioning the cannulae on a smoother sacral surface. This adjustment can help maintain consistent intertip spacing at the periosteal level and promote formation of a continuous lesion.
Parallel placement of cannulae is another critical factor. When cannulae are not parallel, the distance between active tips at the bone surface may exceed the intended spacing, particularly at more proximal levels where anatomical constraints such as the posterior superior iliac spine can complicate access. In ultrasound-guided sacroiliac RFA, for example, achieving parallel placement at the most proximal transverse sacral tubercle was challenging, and deviations from parallelism may have limited the ability to generate a consistent bipolar strip lesion along the periosteum. These observations highlight the importance of meticulous fluoroscopic alignment and cannula trajectory planning when implementing a palisade technique.
Lesion duration and temperature also influence lesion size and the likelihood of complete neural capture. A lesion time beyond two minutes at appropriate temperatures has been suggested to ensure adequate tissue heating for cell death, and some protocols employ 120–180 second lesions at 80–85°C for sacral lateral branch ablation. Additionally, the use of motor stimulation prior to lesioning can help confirm that electrodes are not in proximity to motor fibers, enhancing safety while allowing the operator to maintain a position close to the targeted sensory pathways. Collectively, careful control of spacing, alignment, surface selection, and lesion parameters is essential to realize the theoretical advantages of the bipolar palisade configuration in terms of posterior sacral network capture.
Clinical advantages of lesion standardization
Standardizing the palisade technique on the sacrum aims to reduce variability in lesion geometry and, by extension, in clinical outcomes. Heterogeneity in RFA techniques has been identified as a key factor contributing to the wide range of reported success rates for sacroiliac joint complex neurotomy. By specifying electrode positions along the lateral sacral crest or adjacent smooth surfaces, defining maximum interelectrode distances, and prescribing lesion parameters, the palisade approach provides a reproducible template that can be consistently applied across operators and centers. This standardization is intended to improve the likelihood that the posterior sacral network is comprehensively targeted in each procedure.
The use of larger strip lesions, whether generated by bipolar or cooled RFA, has been recommended to ensure capture of the majority of sacral lateral branches, particularly when combined with a more medial placement of the RF probes along the sacrum. In contrast, monopolar RFA, while clinically effective, often requires multiple cannula passes or periforaminal techniques to approximate similar lesion coverage. A standardized palisade configuration can therefore streamline procedural planning by providing a single, well-defined pattern of cannula placement that is designed to generate a continuous lesion over the key anatomical corridor of the posterior sacral network.
From a broader radiofrequency neurotomy perspective, predictable, reproducible, and repeatable lesion size and shape are core advantages of thermal neurotomy over other neurodestructive techniques. The palisade technique leverages these properties by using a structured multipolar arrangement to produce lesions of known geometry relative to the sacral surface. When combined with pre-lesion motor and sensory stimulation and real-time temperature monitoring, this approach can help ensure that the lesion remains within a safe and effective range while maximizing the length of nerve coagulated along the posterior sacral network.
Ongoing randomized controlled work has been designed to compare bipolar palisade strip lesions with conventional monopolar periforaminal techniques for sacroiliac joint complex pain, reflecting the clinical interest in whether standardized palisade lesioning can translate into improved pain and functional outcomes. Regardless of comparative results, the process of codifying electrode placement, lesion parameters, and adjunctive steps such as L5 dorsal ramus treatment represents a step toward more uniform practice patterns. Such standardization may facilitate more meaningful comparison across studies, support protocol-driven quality improvement, and provide a clearer framework for integrating new technologies, such as multitined electrodes, into sacral RFA practice.
Training and reproducibility in practice
The technical demands of sacral RFA, including precise cannula placement along a complex bony surface and management of multipolar configurations, underscore the importance of structured training for clinicians adopting the palisade technique. Anatomical studies and procedural reviews emphasize that radiofrequency efficacy is highly dependent on positioning of the active electrode tip along the usual course of the target nerve and on maintaining parallel and proximate placement of lesioning electrodes relative to bony landmarks. Training that focuses on fluoroscopic anatomy of the sacrum, recognition of the posterior sacral foraminal apertures and transverse sacral tubercles, and strategies to manage sacral surface undulations is therefore essential for reproducible implementation of the palisade configuration.
Consensus and evidence-based reviews of lateral sacral branch radiofrequency neurotomy highlight the need for careful patient selection using appropriately placed diagnostic blocks and for standardized procedural techniques to optimize outcomes. In this context, the palisade technique offers a defined framework that can be taught and assessed, including specific recommendations for cannula number, spacing, orientation, and lesion parameters. Simulation using anatomical models or cadaveric specimens, combined with stepwise fluoroscopic guidance training, can help clinicians develop the kinesthetic skills required to maintain consistent cannula trajectories and intertip distances along the sacrum.
Reproducibility is further supported by the inherent properties of radiofrequency thermal neurotomy, which allows for predictable lesion size and shape when standard parameters are used, and by the availability of technologies such as multitined expandable electrodes designed to generate large, consistent lesions with technically straightforward maneuvers. When integrated into a palisade configuration, these devices may reduce the number of individual cannula placements required while preserving or enhancing lesion coverage of the posterior sacral network. However, their use still demands adherence to core principles of parallel placement, appropriate spacing, and careful monitoring to ensure that the theoretical advantages of the technique are realized in clinical practice.
Finally, standardized documentation of palisade procedures—including fluoroscopic images in anteroposterior and lateral projections, recorded lesion parameters, and explicit notation of cannula positions relative to sacral landmarks—can facilitate peer review, audit, and iterative refinement of technique. As randomized and observational data comparing bipolar palisade and conventional periforaminal methods emerge, such documentation will be critical for correlating specific technical implementations with clinical outcomes. In this way, training and reproducibility efforts around the palisade technique have the potential not only to improve individual procedural performance but also to advance the broader evidence base for sacral radiofrequency neurotomy.
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