Residency · Residency · Chronic Pain Management

Genicular Nerve Blocks and Radiofrequency Ablation

Introduction

Genicular nerve radiofrequency ablation (RFA) has emerged as an important minimally invasive treatment for chronic knee pain, particularly in patients with knee osteoarthritis who are either not candidates for total knee arthroplasty or wish to delay surgery. This procedure targets the sensory nerves supplying the knee joint capsule, providing durable pain relief without affecting motor function or joint biomechanics.

Anatomy of Genicular Nerve Innervation

Overview

The knee joint receives its sensory innervation from articular branches of several peripheral nerves, collectively termed the genicular nerves. Understanding their course and relationship to bony landmarks is essential for accurate targeting.

Primary Target Nerves

The superior lateral genicular nerve (SLGN) is a branch of the common peroneal nerve that courses along the periosteum at the junction of the lateral femoral epicondyle and the femoral shaft. The superior medial genicular nerve (SMGN), a branch of the tibial nerve (with saphenous nerve contributions), courses along the periosteum at the junction of the medial femoral epicondyle and the femoral shaft. The inferior medial genicular nerve (IMGN), also a branch of the tibial nerve, courses along the periosteum at the junction of the medial tibial condyle and the tibial shaft, deep to the medial collateral ligament.

Additional Genicular Nerves

Beyond the three primary targets, the inferior lateral genicular nerve (ILGN) courses near the fibular head but is less commonly targeted due to its proximity to the common peroneal nerve. The recurrent peroneal nerve supplies the anterolateral knee capsule. The infrapatellar branch of the saphenous nerve (IPBSN) provides sensation to the anterior knee and infrapatellar region and is increasingly recognized as a target for anterior knee pain.

Anatomical Landmarks for Fluoroscopic Targeting

Under fluoroscopy, the SLGN is targeted at the junction of the lateral femoral shaft and the lateral femoral epicondyle at the periosteal surface in AP view. The SMGN is found at the junction of the medial femoral shaft and the medial femoral epicondyle. The IMGN is located at the junction of the medial tibial metaphysis and the medial tibial condyle, deep to the MCL insertion.

<image>Anterior anatomical illustration of the knee joint showing the course and distribution of the genicular nerves, including the superior lateral genicular nerve branching from the common peroneal nerve and coursing over the lateral femoral epicondyle, the superior medial genicular nerve from the tibial nerve running over the medial femoral epicondyle, and the inferior medial genicular nerve crossing the medial tibial condyle beneath the medial collateral ligament, with bony landmarks labeled and fluoroscopic target points marked with crosshairs at each nerve location</image>

Diagnostic Genicular Nerve Block

Rationale

A diagnostic block with local anesthetic is performed prior to radiofrequency ablation to confirm that the genicular nerves are the source of pain and to predict the likelihood of a successful ablation.

Technique

The patient is positioned supine with a small bolster under the ipsilateral knee to achieve slight flexion (10-15 degrees). Using fluoroscopy with an AP view of the knee, the bony landmarks are visualized. A 22-gauge, 3.5-inch spinal needle is advanced to the periosteum at each of the three target sites (SLGN, SMGN, IMGN), and position is confirmed on both AP and lateral fluoroscopic views with the needle tip at the bone surface at each junction landmark. Then 1-2 mL of 0.5% bupivacaine (or 2% lidocaine) is injected at each site, with care taken to avoid excessive volume that could spread to non-target structures.

Response Criteria

A positive diagnostic block is typically defined as 50% or greater pain relief on a numeric rating scale (NRS) during the expected duration of the local anesthetic. Some protocols require dual diagnostic blocks — one with lidocaine, one with bupivacaine — demonstrating concordant results to improve specificity. A more stringent threshold of 80% relief may reduce false positive rates and improve RFA outcomes.

Radiofrequency Ablation Technique

Conventional Thermal RFA

An 18-gauge RF cannula with a 10 mm active tip is placed at the same three periosteal sites used during the diagnostic block. Sensory testing at 50 Hz (up to 0.5 V) should produce concordant paresthesia or pressure at the knee without radiating pain below the knee. Motor testing at 2 Hz (up to 1.0 V) confirms the absence of motor contraction in the lower leg, ruling out proximity to motor nerves. Thermal lesions are then created at 80 degrees Celsius for 90 seconds at each site. The limitation of conventional RFA is that it creates a small, oblate spheroid lesion of approximately 5 mm diameter, making accurate needle placement critical.

Cooled Radiofrequency Ablation

Cooled RFA uses internally cooled electrodes that circulate water to maintain a lower tip temperature (60 degrees Celsius) while allowing tissue temperature to rise further from the electrode tip. This creates a larger lesion (approximately 8-10 mm diameter) compared to conventional RFA, which may improve efficacy by compensating for anatomical variability in genicular nerve location. The COOL-1 trial (Davis et al., 2018) was a randomized controlled trial that demonstrated significant improvement in pain, function (Oxford Knee Score), and global perceived effect at 6 months with cooled RFA compared to intra-articular steroid injection.

<image>Comparative diagram showing lesion size and shape differences between conventional thermal radiofrequency ablation and cooled radiofrequency ablation of a genicular nerve at the medial femoral epicondyle, with the conventional RF electrode producing a small oblate spheroid lesion of approximately 5 mm around the active tip at 80 degrees Celsius, and the cooled RF electrode producing a larger spherical lesion of approximately 8-10 mm with internal water circulation maintaining a 60-degree tip temperature while tissue temperature rises at a distance from the electrode, both shown in cross-section against the femoral periosteum</image>

Patient Selection

Ideal Candidates

The best candidates have moderate to severe knee OA (Kellgren-Lawrence grade 2-4) with pain refractory to conservative management. They may be patients who are not surgical candidates due to medical comorbidities, advanced age, or patient preference, or those seeking a bridge to arthroplasty or pain reduction to facilitate rehabilitation. A positive diagnostic genicular nerve block (greater than 50% relief) is mandatory before proceeding to RFA.

Less Ideal Candidates

Patients with primarily anterior knee pain may require IPBSN targeting in addition to standard genicular nerves. Post-arthroplasty pain presents challenges because altered anatomy may affect accuracy, though emerging evidence supports use in this population. Patients with diffuse, poorly localized knee pain or significant central sensitization tend to have poorer outcomes. Those with inflammatory arthritis in active flare should have systemic treatment optimized first.

Evidence Base

Key Clinical Trials

Choi et al. (2011) published the first RCT demonstrating efficacy of genicular nerve RFA, with significant pain reduction at 12 weeks compared to sham. Davis et al. (2018) published the COOL-1 multicenter RCT showing cooled RFA was superior to a single corticosteroid injection at 6 months for knee OA pain. McCormick et al. (2017) reported a retrospective study showing 65% of patients achieved greater than 50% pain relief at 6 months after conventional genicular RFA. The duration of effect is typically 6-12 months before nerve regeneration may necessitate repeat ablation.

Comparison with Other Treatments

Genicular nerve RFA provides longer duration of relief compared to intra-articular corticosteroid injections. It may be combined with viscosupplementation or PRP for comprehensive management and does not preclude or complicate future total knee arthroplasty.

<image>Fluoroscopic AP view of the knee during genicular nerve radiofrequency ablation showing three RF cannulae positioned at the three standard target sites — one at the junction of the lateral femoral shaft and epicondyle for the SLGN, one at the junction of the medial femoral shaft and epicondyle for the SMGN, and one at the junction of the medial tibial shaft and condyle for the IMGN — with labeled bony landmarks and cannula active tips in direct contact with the periosteum</image>

Complications

Post-procedure pain and swelling is the most common complication and is self-limited over 1-2 weeks. Transient skin numbness (hypoesthesia over the medial or lateral knee) usually resolves. Infection is rare with aseptic technique. Motor nerve injury is uncommon and the risk is minimized by motor stimulation testing prior to lesioning — this is particularly important for the ILGN due to its proximity to the common peroneal nerve. Burns can occur if the grounding pad is not properly placed for conventional RFA.

Clinical Pearls

Periosteal placement is critical because the genicular nerves travel along the periosteum, and even 2-3 mm of distance can result in an ineffective lesion. Performing dual diagnostic blocks with different local anesthetics improves patient selection and predicts better RFA outcomes. Cooled RFA may be preferred over conventional RFA due to its larger lesion size and stronger RCT evidence, particularly when anatomical variability is a concern. After RFA, patients should begin a structured physical therapy program to capitalize on pain reduction and improve knee function. Genicular nerve RFA can be safely repeated when pain returns after nerve regeneration, with similar efficacy to the initial procedure.

References

1. Choi WJ, Hwang SJ, Song JG, et al. Radiofrequency treatment relieves chronic knee osteoarthritis pain: A double-blind randomized controlled trial. Pain. 2011;152(3):481-487.
2. Davis T, Loudermilk E, DePalma M, et al. Prospective, multicenter, randomized, crossover clinical trial comparing the safety and effectiveness of cooled radiofrequency ablation with corticosteroid injection in the management of knee pain from osteoarthritis. Reg Anesth Pain Med. 2018;43(1):84-91.
3. McCormick ZL, Korn M, Reddy R, et al. Cooled radiofrequency ablation of the genicular nerves for chronic pain due to knee osteoarthritis: Six-month outcomes. Pain Med. 2017;18(9):1631-1641.
4. Franco CD, Buvanendran A, Petersohn JD, Menzies RD, Menzies LP. Innervation of the anterior capsule of the human knee: Implications for radiofrequency ablation. Reg Anesth Pain Med. 2015;40(4):363-368.

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