Osteoarthritis (OA) of the knee is very common, with approximately 33%–85% of people older than 55 years exhibiting radiographic evidence of the disease. All-cause knee pain is present in 20%–30% of those aged 65 and older. ^[1] Knee pain affects 250 million people worldwide, and that number is expected to increase as the population ages and knee pain from OA becomes more common. Risk factors for OA-induced knee pain include high body mass index (BMI), previous joint injury, occupational hazards that place excessive mechanical stress on the knee joint, and structural misalignment. Chronic knee pain leads to disability, psychological distress, and impaired quality of life.

Signs and symptoms of OA of the knee include pain that increases with activity and improves with rest, swelling, feeling of warmth, stiffness especially in the morning or after a period of inactivity, crepitus, and decreased range of motion.

Because of the lack of optimal treatment options, alternative methods are needed to manage patients with knee pain that results from OA. A relatively novel option is radiofrequency (RF) ablation of the genicular nerves

Treatment includes conservative options such as physical therapy, anti-inflammatory drugs, and injections with steroids or hyaluronic acid. A recent study found greater cartilage loss and no significant difference in knee pain with 40 mg of intra-articular triamcinolone compared to placebo (saline) at two years.^[2] Other studies on efficacy of hyaluronic acid injections demonstrate confounding results.

For severe pain or those who have failed to respond to conservative treatment, total knee arthroplasty (TKA) is an option. The procedure has perioperative and postoperative risks, including development of chronic pain (approximately 20%) and limited implant longevity. In addition, not all patients are eligible for a TKA secondary to young age, high BMI, or medical comorbidities.^[3]

Nonsteroidal anti-inflammatory agents may help manage the pain; however, they are associated with significant risks, including gastric bleeding and increased cardiovascular events. Duloxetine, which is U.S. Food and Drug Administration approved for the treatment of musculoskeletal pain, can also be used. Use of opioids can lead to numerous side effects, including dependence, tolerance, hyperalgesia, endocrine imbalance, and addiction.

Because of the lack of optimal treatment options, alternative methods are needed to manage patients with knee pain that results from OA. A relatively novel option is radiofrequency (RF) ablation of the genicular nerves. Genicular nerves arise from branches of the tibial and common peroneal nerves. The tibial nerve gives rise to the superior and inferior medial genicular nerves. The common peroneal nerve gives rise to the superior lateral genicular nerve and inferior lateral genicular nerve; however, the latter is not targeted during RF because of its close proximity to the common peroneal nerve and the risk for foot drop. A branch of the vastus intermedius may be a fourth nerve target, particularly for subpatellar pain. (See Figure 1.)

Thermal or internally cooled RF ablation can be used to denervate the genicular nerves. The target for the superior medial, superior lateral, and the inferior medial inferior medial genicular nerves is the junction between the femoral or tibial shaft and the epicondyle. The target for the branch from the vastus intermedius is approximately 2 cm above the patella in the midline. If using traditional RF ablation, multiple lesions at each target should be performed. (See Figure 2.) The condyles should be properly aligned to accurately gauge depth of needle insertion (see Figure 3), and the needles should be inserted approximately two-thirds of the distance across the femoral shaft for the superior medial and superior lateral genicular nerves and approximately halfway across the tibial shaft for the inferior medial genicular nerve. RF lesioning should be performed after appropriate sensory and motor testing.

Randomized controlled trials have demonstrated efficacy of using RF ablation for denervation of the genicular nerve. Choi et al.⁴ performed a double-blinded and randomized controlled trial that compared the efficacy of genicular RF ablation to a sham procedure. They found a statistically significant decrease in visual analog scores (VAS) in the RF group compared to the sham. In addition, patients reported significant functional improvement and satisfaction with the treatment at three months’ follow-up.^[4]

Davis et al.^[5] compared the effectiveness and safety of cooled RF ablation with corticosteroid injections in patients with knee OA. All patients underwent a diagnostic block of the superior medial, superior lateral, and inferior medial genicular nerves. If patients reported a 50% reduction in their numeric rating score (NRS), they were randomized to receive a single, intra-articular injection of a corticosteroid or cooled RF ablation. Significant reductions in NRS scores, oxford knee scores, and global perceived effect up to six months were found in the cooled RF ablation group, and the procedure had no reported side effects from the procedure.^[5] Another study is underway comparing the effectiveness of cooled RF ablation to a single intra-articular injection of hyaluronic acid.

RF denervation of the genicular nerves is generally considered safe; however, potential complications include bleeding, infection, pain at the procedure site, and skin burn. When performing the procedure, verify that the electrode tip is deep enough in the soft tissue to prevent skin burn.

Although more research is required, RF ablation for alleviation of OA-related knee pain deserves consideration as a mechanism to reduce opioid administration, decrease pain, and improve quality of life.

Figure 1: Anteroposterior Visual of the Knee

Radiographs in the anteroposterior (A) and lateral (B) views detail the stainless-steel wires that were placed along four of the nerve branches supplying the anterior capsule of the knee. C is an anteroposterior view, where the white arrows note the branch from the vastus intermedius that approximates a course along the midline of the anterior femur.

Printed with permission from Franco C, Buvanendran A, Petersohn J, et al. Innervation of the anterior capsule of the human knee: implications for radiofrequency ablation. Reg Anesth Pain Med. 2015;40:363–368.

Figure 2: Targets for Traditional Radiofrequency Ablation 

Final needle position in anterioposterior and lateral views of the superior medial and lateral genicular nerves and the inferior medial genicular nerve.

Printed with permission from Halyard Health, Inc.

Figure 3: Incorrect Epicondyle Alignment

Lateral view showing improper alignment of the epicondyles.

Printed with permission from Halyard Health, Inc. 

References:

1. Mannoni A, Briganti MP, Di Bari M, et al. Epidemiological profile of symptomatic osteoarthritis in older adults: a population based study in Dicomano, Italy. Ann Rheum Dis. 2003;62:576–578. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1754567/
2. McAlindon TE, LaValley MP, Harvey WF, et al. Effect of intra-articular triamcinolone vs saline on knee cartilage volume and pain in patients with knee osteoarthritis: A randomized clinical trial. 2017;317(19):1967–1975. https://doi.org/10.1001/jama.2017.5283
3. Weinstein AM, Rome BN, Reichmann WM, et al. Estimating the burden of total knee replacement in the United States. J Bone Joint Surg Am. 2013;95:385– https://doi.org/10.2106/JBJS.L.00206
4. Choi W, Hwang SJ, Song JG, et al. Radiofrequency treatment relieves chronic knee osteoarthritis pain: a double-blind randomized controlled trial. 2011;152:481–487. https://doi.org/10.1016/j.pain.2010.09.029
5. Davis T, Loudermilk E, DePalma M, et al. Prospective, multicenter, randomized, crossover clinical trial comparing the safety and effectiveness of cooled RF ablation with corticosteroid injection in the management of knee pain from osteoarthritis. Reg Anesth Pain Med. 2018;43:84– https://doi.org/10.1097/AAP.0000000000000690