A Proposed Protocol for Safe Radiofrequency Ablation of the Recurrent Fibular Nerve for the Treatment of Chronic Anterior Inferolateral Knee Pain

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Dear Editor, Fluoroscopically guided radiofrequency ablation (RFA) of the genicular nerves is increasingly utilized for the treatment of chronic pain secondary to knee osteoarthritis (OA) and for management of persistent pain after knee arthroplasty. The originally described protocol for this procedure involves targeting the superior lateral genicular nerve (SLGN), superior medial genicular nerve (SMGN), and inferior medial genicular nerve (IM) [1]. Studies evaluating RFA for the treatment of pain due to knee OA using this traditional technique with minor modifications have demonstrated fair to good clinical outcomes, though these studies have generally been small or limited by methodological shortcomings [1–3]. These findings are consistent with practice audit data in a real-world knee OA population that showed only fair outcomes [4], with late-stage OA predicting a greater likelihood of treatment failure [5]. Controlled studies aimed at preemptively reducing pain in the postoperative period following knee arthroplasty and in patients with chronic pain despite arthroplasty failed to demonstrate superiority compared with sham intervention [6, 7] and genicular nerve block [8], respectively. Although certain demographic, clinical, and radiographic factors may predispose patients to treatment failure with genicular nerve RFA, failure to successfully target the nociceptive innervation using the traditional three-nerve protocol may also contribute to suboptimal outcomes. Recently, descriptions of sensory articular innervation to the knee have identified discrepancies between the target sites for the three traditional genicular nerves treated in past studies and have described terminal articular nerves [9–11]. Further, studies have identified additional landmarks in the knee suitable for genicular RFA that are not currently included in the traditional genicular RFA protocol [10, 11]. These discrepancies may account for suboptimal treatment outcomes in a proportion of patients. Previously, we described a new protocol to more effectively capture the SLGN, SMGN, and IMGN genicular nerves, as well as the articular nerves from the nerve to vastus lateralis (NVL), intermedius (NVI), and medialis (NVM) [12]. However, this protocol does not address innervation to the inferolateral portion of the anterior knee joint capsule. This region receives innervation from the recurrent fibular nerve (Figures 1A and 2A). Clinicians have generally avoided targeting the recurrent fibular nerve due to concern about lesioning the common fibular nerve, which may result in weakness of ankle dorsiflexion. Conversely, RFA of spinal medial branch nerves (MBNs) is commonly performed despite the close proximity of the ablation site to the exiting nerve roots from the neuroforamina. When appropriate risk mitigation strategies are implemented, successful MBN RFA without damage to the adjacent nerve root and/or ventral ramus is well characterized despite less predictable RFA lesioning patterns at bone–muscle interfaces [13, 14]. Here, we present a technical description for proposed safe capture of the recurrent fibular nerve to address inferolateral anterior knee pain. A) Anterior-posterior radiographic image of the knee with representation of the variable course of the recurrent fibular nerve (dashed lines) based on dissections by Tran et al. [8]. B) Lateral radiographic image of the knee with representation of the variable course of the recurrent fibular nerve (dashed lines) based on dissections by Tran et al. [8]. A) Anterior-posterior radiographic image of the knee with representation of the variable course of the recurrent fibular nerve (dashed lines) based on dissections by Tran et al. [8]. B) Lateral radiographic image of the knee with representation of the variable course of the recurrent fibular nerve (dashed lines) based on dissections by Tran et al. [8]. A) Anterior-posterior fluoroscopic image of the knee in a patient with a native knee. Representation of the variable course of the recurrent fibular nerve based on dissections by Tran et al. [8] is shown in relation to the final conventional radiofrequency electrode position for ablation of the recurrent fibular nerve. B) Lateral fluoroscopic projection of final radiofrequency electrode position for ablation of the recurrent fibular nerve in a patient with a native knee. Representation of the variable course of the recurrent fibular nerve (dashed lines) based on dissections by Tran et al. [8] is shown in relation to the anterior border of the fibular head (large solid line). Note that in this image the electrode tip is positioned 1–2 mm anterior to the fibular head as minimal forward projection of the radiofrequency lesion is anticipated when using conventional technology. A) Anterior-posterior fluoroscopic image of the knee in a patient with a native knee. Representation of the variable course of the recurrent fibular nerve based on dissections by Tran et al. [8] is shown in relation to the final conventional radiofrequency electrode position for ablation of the recurrent fibular nerve. B) Lateral fluoroscopic projection of final radiofrequency electrode position for ablation of the recurrent fibular nerve in a patient with a native knee. Representation of the variable course of the recurrent fibular nerve (dashed lines) based on dissections by Tran et al. [8] is shown in relation to the anterior border of the fibular head (large solid line). Note that in this image the electrode tip is positioned 1–2 mm anterior to the fibular head as minimal forward projection of the radiofrequency lesion is anticipated when using conventional technology. The patient is placed in a supine position, and the index knee is flexed 30° using a bolster. This placement facilitates a clear lateral view of the knee. After prepping and draping the knee, fluoroscopic scout images are used to align the tibial plateau in a true anterior-posterior (AP) view. A skin wheal is placed 0.5–1 cm lateral to the lateral tibial condyle at the cranio-caudal level of the lower third of the fibular head. One mL of 1% lidocaine is administered to anesthetize the skin and neighboring subcutaneous tissues before cannula insertion superficial to the recurrent fibular nerve. The cannula is advanced through the skin wheal. From this slightly lateral entry point, the needle is advanced until it contacts the periosteum of the lateral tibial condyle; the stylet tip is positioned at the cranio-caudal level of the lower third of the fibular head. We recommend avoiding periosteum contact until final advancement to minimize patient discomfort. A true lateral fluoroscopic view is then obtained by superimposing the femoral condyles, and the cannula is repositioned until the stylet tip is positioned 1–2 mm anterior to the fibular head. Care should be taken to ensure that adequate soft tissue is present superficial to the probe in order to decrease risk of thermal injury to the skin, especially in patients with minimal musculature and/or subcutaneous tissue in this area. Distance from the RFA lesion to skin may be enhanced by “lifting” the skin away from the periosteum using saline infiltration or additional local anesthetic (following motor testing). Care should also be taken to avoid inadvertent penetration of the tibiofibular joint capsule with excessive posterior placement. The stylet is removed, and the RFA electrode is inserted (Figures 2A, B, 3A, B). The electrode is then adjusted as needed to create an anticipated lesion slightly anterior to the fibular head as visualized in a true lateral view (Figures 2B and 3B). There is slight variability of electrode tip positioning depending on the RFA technology being utilized for the procedure. When cooled RFA technology is used, this necessitates an electrode tip position 4–5 mm anterior to the fibular head in a lateral view. Alternatively, when using conventional radiofrequency technology, the electrode tip should be positioned 1–2 mm anterior to the fibular head in a lateral view to ensure creation of an adequate lesion given the more parallel lesion geometry as opposed to forward lesion projection of traditional RFA. An AP view is rechecked to ensure correct electrode placement adjacent to the lateral tibial condyle periosteum in this plane (Figures 2A and 3A). This position is consistent with recent anatomic work [9–11]. Motor testing is performed at 2 Hz and 2 mV in order to ensure adequate distance from the common fibular nerve. Then, 1–2 mL of local anesthetic is administered to anesthetize the recurrent fibular nerve. The ablation is performed using described parameters depending on the technology [15]. If conventional RFA technology is used, the physician may consider placing two adjacent lesions in the cephalo-caudal plane in order to increase the likelihood of recurrent fibular nerve capture, as the conventional electrode may not be perfectly perpendicular to the target nerve fibers, as would be ideal when this technology is used. A) Anterior-posterior fluoroscopic image of the knee in a patient with a total knee arthroplasty (TKA). Representation of the variable course of the recurrent fibular nerve based on dissections by Tran et al. [8] is shown in relation to the final cooled radiofrequency electrode position for ablation of the recurrent fibular nerve. The anticipated zone of radiofrequency lesion development is shown by the white circle. B) Lateral fluoroscopic projection of final radiofrequency electrode position for ablation of the recurrent fibular nerve in a patient with TKA. Representation of the variable course of the recurrent fibular nerve (dashed lines) based on dissections by Tran et al. [8] is shown in relation to the anterior border of the fibular head (large solid line), the electrode tip (small solid line), and the anticipated zone of radiofrequency lesion development (white circle). Note that in this image the electrode tip is positioned 3–4 mm anterior to the fibular head as forward projection of the radiofrequency lesion is anticipated when using cooled technology. A) Anterior-posterior fluoroscopic image of the knee in a patient with a total knee arthroplasty (TKA). Representation of the variable course of the recurrent fibular nerve based on dissections by Tran et al. [8] is shown in relation to the final cooled radiofrequency electrode position for ablation of the recurrent fibular nerve. The anticipated zone of radiofrequency lesion development is shown by the white circle. B) Lateral fluoroscopic projection of final radiofrequency electrode position for ablation of the recurrent fibular nerve in a patient with TKA. Representation of the variable course of the recurrent fibular nerve (dashed lines) based on dissections by Tran et al. [8] is shown in relation to the anterior border of the fibular head (large solid line), the electrode tip (small solid line), and the anticipated zone of radiofrequency lesion development (white circle). Note that in this image the electrode tip is positioned 3–4 mm anterior to the fibular head as forward projection of the radiofrequency lesion is anticipated when using cooled technology. We describe a proposed technique for the safe capture of the recurrent fibular nerve based on recent anatomical studies suggesting that this nerve provides nociceptive input from the inferolateral portion of the anterior knee joint capsule [9–11]. In order to validate the accuracy and safety of this technique, both cadaveric dissection studies and clinical outcome studies will be needed. Omitting the recurrent fibular nerve from genicular nerve RFA protocols due to concern about damage to the common fibular nerve may be myopic and could lead to suboptimal treatment outcomes, namely inadequate pain relief and function in some patients. Further, as a modality, the precision and predictability of RFA may be uniquely suited to addressing pain transmitted by the recurrent fibular nerve. In contrast, chemoneurolysis may be more likely to result in damage to the common fibular nerve given its less predictable region of tissue destruction compared with RFA. Likewise, if a prognostic block of the recurrent fibular nerve is performed, the physician should consider the lack of predictability of anesthetic agent flow compared with the tissue volume that would be captured by a subsequent RFA lesion. We have reported on this consideration previously [16, 17], but further study will be needed to define appropriate prognostic block volume thresholds specific to the recurrent fibular nerve. Finally, while we present a protocol that mirrors the risk mitigation strategies used to prevent spinal nerve root and/or ventral ramus damage during MBN RFA, outcome studies will be necessary to confirm the safety of this technique. Funding sources: There were no sources of funding. Disclosure and conflicts of interest: Zachary L. McCormick, MD, serves on the Board of Directors of the Spine Intervention Society. There are no other potential conflicts of interest to disclose on the part of any of the other authors. There were no sources of support for this study.