Therapeutic effect of fluoroscopy-guided genicular nerve radiofrequency ablation for chronic knee pain: A retrospective clinical study

INTRODUCTION

Osteoarthritis (OA) is the most prevalent arthritic condition globally, characterized by localized degradation of articular cartilage, osteophyte formation, and alterations in joint morphology.^[1] Chronic knee OA is especially common in the elderly population, constituting one of the most frequently encountered degenerative joint disorders in later life.^[2] The condition is characterized by gradual deterioration of cartilage resilience and progressive wearing of the articular surface.^[3] Approximately 40% of older adults are estimated to have knee OA, with obesity serving as a significant predisposing factor.^[4,5] Severe symptomatic knee OA has been documented in roughly 37% of those aged over 60 years.^[6]

In Saudi Arabia, an earlier investigation documented a prevalence of 13%, whereas a subsequent survey conducted in 2018 reported a prevalence of 24.5% among individuals aged 60 years and older, with comparable rates among males (26.1%) and females (26.8%).^[1,7]

From a clinical perspective, OA manifests as pain, disrupted sleep patterns, and impaired mobility.^[2] Knee pain is the principal clinical feature of OA and is linked to fatigue, functional limitations, loss of autonomy, and low mood.^[8] It typically presents as unilateral or bilateral knee pain, diminished function, restricted joint movement, and eventual disability.^[6]

Standard treatment for symptomatic knee OA encompasses physical therapy, lifestyle modification, injections, and pharmacotherapy.^[6] Nevertheless, drug-based interventions offer only modest symptom relief, and the use of non-steroidal anti-inflammatory drugs (NSAIDs) is associated with considerable adverse effects, including gastrointestinal ulceration, hemorrhage, and renal damage.^[9,10] Additional non-operative modalities such as acupuncture, periosteal stimulation, and intra-articular administration of hyaluronic acid or corticosteroids may function as supplementary treatments but frequently prove insufficient for sustained management of chronic severe knee pain.^[2]

Genicular nerve radiofrequency ablation (RFA) represents an alternative interventional approach.^[6] The genicular nerves, which originate from articular branches of the femoral, saphenous, common peroneal, tibial, and obturator nerves, supply sensory innervation to the knee joint.^[11,12] Thermal ablation of these nerves disrupts nociceptive signaling and may facilitate functional recovery.^[2]

Two principal RFA modalities exist: Pulsed and continuous. Pulsed RFA applies intermittent energy bursts at comparatively low temperatures, achieving neuromodulatory effects at the cellular level while causing minimal tissue injury.^[13-15] Continuous RFA, by contrast, produces thermal coagulation of nerve fibers through sustained heating at the electrode tip.^[13,14] This modality can be subdivided into conventional RFA (conducted at approximately 80°C, generating an elliptical lesion) and cooled RFA (utilizing a water-cooled probe at roughly 60°C, creating a larger spherical lesion).^[16] Building on earlier reports of continuous RFA, the present study assessed the short-term effect of image-guided genicular nerve RFA (GnRF) on chronic knee pain in an ambulatory care setting.

MATERIALS AND METHODS

Radiofrequency ablation procedure

A diagnostic genicular nerve block was performed in all patients 1 week before the procedure, and only those who reported greater than 50% pain relief after the block proceeded to RFA. The procedure was carried out using an 80-watt COOLIEF Cooled Radiofrequency generator (models CRG-Advanced or PMG-Advanced; Avanos Medical) with a 17-gauge radiofrequency cannula incorporating a 4-mm active tip. Before ablation, a local anesthetic (1–2 mL of 1% lidocaine) was infiltrated at each site to anesthetize the skin and soft tissues at the puncture site and to bathe the targeted genicular nerves.

Using fluoroscopic guidance with an image intensifier, a radiofrequency needle was inserted percutaneously toward the junction between the condyle or epicondyle and the diaphysis of the femur and tibia, targeting the superior medial, superior lateral, and inferior medial genicular nerves. A radiofrequency electrode was subsequently advanced through the needle [Figure 1].

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Figure 1: Fluoroscopic images of the left knee demonstrating needle and electrode placement. (a) Lateral view showing the introducer needle positioned at the target genicular nerve region along the distal femur. (b) Anteroposterior view confirming accurate needle placement at the medial and lateral genicular nerve targets. A radiofrequency electrode was subsequently advanced through the needle to perform nerve ablation. AP: Anteroposterior

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Sensory testing was carried out at 50 Hz (1.2 V and 1.6 V), and motor testing was conducted at 2 Hz with stepwise voltage increases of 0.5 V up to 3 V to verify the absence of motor activation. Following confirmation of appropriate needle positioning, the electrode tip was heated to 60°C for 180 s, generating a single lesion at each targeted genicular nerve.

RESULTS

The analysis included 21 patients (13 women and 8 men) with a mean age of 62.7 ± 5.7 years (range 50–70). All were Saudi nationals with Kellgren–Lawrence grade 3–4 knee OA who had failed prior conservative management and had reported greater than 50% pain relief following a diagnostic genicular nerve block 1 week before the procedure. The cohort was predominantly overweight or obese (mean body mass index 30.3 ± 7.2 kg/m²; 11 patients [52.4%] were obese), and the most common comorbidities were type II diabetes mellitus (11 patients, 52.4%), hypertension (10 patients, 47.6%), and hyperlipidemia (7 patients, 33.3%); six patients (28.6%) had no documented comorbidity. The procedure was performed bilaterally in 9 patients (42.9%) and unilaterally in 12. Full baseline characteristics are summarized in Table 1. Mean VAS pain scores showed a substantial, consistent decline throughout the follow-up period. The baseline VAS score of 8.9 ± 0.7 dropped to 4.7 ± 0.9 at 3 months, 3.3 ± 0.9 at 6 months, and 2.4 ± 0.9 at 1 year [Table 2].

A repeated-measures ANOVA revealed a statistically significant effect of time on VAS scores (p < 0.001). Post hoc pairwise comparisons with Holm correction demonstrated significant pain reductions between baseline and each subsequent follow-up point (all p < 0.001). Further analyses confirmed additional decreases between 3 and 6 months (p < 0.001) and between 6 months and 1 year (p < 0.001) [Table 3].

The scatter plot [Figure 2] illustrates individual patient VAS pain scores at baseline (before the intervention) and at 1 year following the procedure. No procedure-related complications were recorded in this sample, given the small number of patients.

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Figure 2: Scatter plot demonstrating individual patient Visual Analog Scale scores at baseline and 1 year after the radiofrequency ablation procedure. VAS: Visual Analog Scale.

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DISCUSSION

Knee OA constitutes a leading contributor to activity restriction and physical disability arising from pain and compromised functional capacity. In Saudi Arabia, it stands among the most prevalent and rapidly expanding health concerns.^[17] Pain accompanying severe OA frequently responds inadequately to conservative approaches, with chronic pain persisting in over 40% of affected individuals.^[18]

In recent years, RF-based procedures, particularly RFA, have gained prominence as therapeutic alternatives for patients with severe joint pain who are either unwilling or medically unfit for total knee arthroplasty, yielding encouraging clinical outcomes.^[19] RFA induces thermally mediated tissue damage within a well-defined, uniform lesion.^[20] A key advantage of this technique is the precise localization of heat to a narrow zone (<1 mm) of tissue in direct contact with the ablation electrode, achieving temperatures of ≥40–50°C.^[21,22]

In the present investigation, a notable decrease in pain was evident as early as 3 months post-intervention. Mean pain scores fell from 8.9 before the procedure to 4.7 at 3 months, then continued to decline to 2.4 at 1 year. Pain intensities at the 1-year follow-up remained well below baseline, which is consistent with a sustained reduction in reported pain in this uncontrolled case series; without a comparator group, however, this cannot be separated from the natural course of pain or a placebo response.

These findings are consistent with prior research. A study involving 48 patients who underwent GnRF demonstrated a significant decline in VAS pain scores at one, three, and 6 months following the procedure relative to baseline p < 0.001).^[23] Although our follow-up period extended to 1 year, the early trajectory of pain improvement closely paralleled their reported outcomes.

A pooled analysis of 15 randomized controlled trials encompassing 1,009 patients confirmed that RF therapy significantly enhanced pain outcomes (VAS/NRS) and knee function at 1–2, 4, and 24 weeks post-treatment (p < 0.001).^[19] Likewise, a retrospective chart review evaluating pain relief at three and 6 months documented a mean improvement of 67% from baseline at 3 months.^[24] A comprehensive review of 33 studies published from 2011 to 2020 further corroborated that GnRF produces sustained improvements in pain and function that persist for 3–12 months.^[25]

Jamison and Cohen analyzed nine clinical trials comprising 592 patients and observed significant pain reduction and functional gains lasting 3–12 months.^[18] In the present series, reduced pain scores persisted through the 1-year follow-up, in keeping with these reports, although a controlled comparison would be needed before attributing this persistence to RFA itself.

In a separate controlled trial, patients receiving percutaneous RF genicular neurotomy under fluoroscopic guidance were compared against those undergoing the same procedure without effective neurotomy. Assessment using both VAS and Oxford Knee Scores revealed significant improvements in pain and function within the RFA group.^[2] By contrast, the present study relied exclusively on the VAS for pain evaluation.

Sluijter et al. additionally documented complete pain elimination through intra-articular pulsed RF in cases of refractory post-traumatic knee pain.^[26] Moreover, a systematic review comprising eleven studies (265 patients) that examined GnRF for persistent post-arthroplasty knee pain reported favorable responses in 30–100% of patients, although the certainty of evidence remained low owing to study heterogeneity and risk of bias.^[6]

Nonetheless, not all investigations yielded positive results. One trial assessing bipolar RFA targeting the superomedial, inferomedial, and superolateral genicular nerves did not find a statistically significant difference between active and sham RFA (combined with local anesthetic and corticosteroid injection) in clinically meaningful pain reduction.^[27] This negative result deserves attention. Several factors may explain why it differed from the present and other positive studies. That trial used a bipolar technique rather than the conventional or cooled monopolar approach applied here. Its sham comparator also included an active local anesthetic and corticosteroid injection, which may itself have produced analgesia and reduced the apparent treatment effect, and the targeted nerves differed from the present protocol. The post-arthroplasty systematic review^[6] also reported low-certainty evidence, which the authors attributed to small samples, varied techniques, and risk of bias. Together, these findings indicate that the efficacy of GnRF is not yet firmly established and that patient selection, ablation modality, and choice of comparator all affect the reported outcomes. The uncontrolled, single-arm design of the present study also cannot exclude a placebo contribution to the observed pain relief.

CONCLUSION

In this small, uncontrolled retrospective case series, GnRF was associated with a statistically significant and progressive decline in VAS pain scores across the 1-year follow-up, as shown by repeated-measures ANOVA and post hoc analyses. Scores fell from baseline and continued to decrease at each subsequent assessment, consistent with a sustained reduction in reported pain within the limits of an uncontrolled design.

These preliminary findings suggest that GnRF may be a useful minimally invasive option for chronic knee pain related to OA. Given the small sample, the absence of a control group, and the lack of functional and safety endpoints suited to a study of this size, the results should be read as hypothesis-generating rather than as evidence of efficacy or safety. Pending confirmation in larger controlled studies with longer follow-up, RFA may have a place within multimodal pain management, particularly for patients who are not candidates for joint replacement or who wish to defer it.