The purpose of this study is to investigate the efficacy and safety of pulsed radiofrequency of the saphenous nerve in the treatment of pain due to knee osteoarthritis (OA). The investigators will conduct real pulsed radiofrequency or sham, over the saphenous nerve during 4 separate sessions. The investigators will evaluate pain intensity, quality of life, function, and disability via clinical validated scales.

The research question is whether pulsed radiofrequency can lessen knee pain and improve function and quality of life in patients with chronic knee pain due OA.

It is hypothesized, that less knee pain and improved function, and quality of life after the pulsed radiofrequency sessions.

Osteoarthritis (OA) affects 10% of the population over 60 years of age each year, with an increasing incidence related to population aging. This disease costs 1-2.5% of GDP on average in Europe when combining direct and indirect costs: it is therefore the 9th leading cause of disability adjusted life years. The knee is the most commonly affected joint, for which there is no treatment able to stop joint degeneration as of today: common treatment regimens include pharmacological therapy, joint infiltrations, neuromodulation techniques, and total knee arthroplasty when indicated. However, each patient responds differently and therefore necessitates a tailored approach.

Pulsed radiofrequency (PRF), a neuromodulating technique that potentiates the descending analgesic pathway by avoiding Wallerian degeneration, has as of today been targeted intraarticularly or to the genicular nerves, yielding unreliable results in both cases, perhaps due to small samples, lack of long term follow ups, and absence of control groups.

The goal of this study is to explore the efficacy and safety of PRF on the saphenous nerve, an exclusively sensory nerve that is responsible for pain perception on the medial surface of the lower limb, often associable with OA. In particularly, the investigators will evaluate the effect of PRF on pain reduction, function, disability, and quality of life in patients with knee OA.

This study will include 20 participants suffering from knee OA, and the participants will enroll if infiltrating their saphenous nerve with 2mL of 2% lidocaine reduces their Numeric Pain Rating Scale (NRS) pain perception by at least 60%.

The participants will be allocated consecutively to randomization as an intervention order using the tool from the randomization.com website (Dallal GE, http://www.randomization.com). The investigators will use the second generation suggested for crossover studies. The participants will be randomized into a PRF sham control group or a real PRF group and the investigators will follow up at 2 weeks (T1), 1 month (T2), 3 months (T3), and 6 months (T4) by acquiring their NRS, Oxford Knee Score, and SF-36 questionnaire. After 6 months, the participants will be crossed-over and the follow-up method will be repeated.

Inclusion Criteria:

• Chronic knee pain (present for at least 6 months), of moderate-severe intensity (assessed by NRS => 6), not responsive to conservative treatments (physiotherapy, oral analgesics).
• Diagnosis of knee osteoarthritis confirmed by instrumental investigation (X-ray and/or MRI) and Oxford Knee Score = <35.
• Positivity to the diagnostic block of no. saphenous (defined as a reduction of at least 50% of the NRS score).
• If the patient is taking opioids or other morphine equivalents, the dosage should not be changed within 3 months prior to the study enrollment visit.

Exclusion Criteria:

• Body Mass index > 40 kg /m2
• History of systemic inflammatory disease, uncontrolled diabetes mellitus, neoplastic pathology, coagulopathy
• Previous knee replacement implant