Radiofrequency Ablation for the Treatment of Post-knee Arthroplasty Chronic Pain. A Randomized Double-blind Study. A Novel Approach.

Degenerative knee osteoarthritis pain is one of the main reasons for consultation in general and specialized medicine. Its assessment and treatment impose a high cost on healthcare systems, accounting for 0.5% of Spain's gross domestic product. Given the magnitude of the disease and the disability it causes in affected individuals, multiple therapies have been proposed, ranging from pharmacological therapy with nonsteroidal anti-inflammatory drugs, opioids, antidepressants, capsaicin cream treatment, and physiotherapy, to intra-articular treatments with corticosteroids and viscosupplements like hyaluronic acid, platelet-rich plasma, etc. Knee arthroplasty is one of the most successful orthopedic surgeries in current medicine, significantly improving pain, disability, and the overall quality of life for patients who undergo it. However, postoperative pain following knee arthroplasty remains a challenging problem, with incidence rates of pain and disability after the procedure ranging from 48% to 34%, respectively, at 3 and 6 months post-surgery, with iatrogenic nerve injury being the most common cause. There are limited therapeutic alternatives available from this point onwards.

Since the first description of using radiofrequency for the treatment of intractable chronic pain, it has become not only a tool for pain management but also a cornerstone in pain units' treatment. The use of radiofrequency ablation for pain is based on the premise that the transmission of radiofrequency current near nociceptive pathways would interrupt the pain stimulus through the destruction of the nervous tissue. Thermal radiofrequency has been successfully used in the treatment of facetogenic low back pain, sacroiliac joint pain, and discogenic low back pain.

In the year 2011, the first study was conducted on radiofrequency of the sensory nerves of the knee, known as the genicular nerves, using femoral and tibial condyles as anatomical references and fluoroscopy as an imaging guide. Unfortunately, discrepancies in terminology and anatomical descriptions have led to confusion among interventional physicians. Other researchers have demonstrated discrepancies with the studies published in 2011, making it more difficult to standardize the technique of neuroablation of these nerves. More recently, other researchers demonstrated a specific anatomical-ultrasound correlation of sensory terminal branches of the femoral and sciatic nerves that innervate the knee. The involved nerves include the infrapatellar branch of the saphenous nerve, the nerve to the medial vastus muscle, the nerve to the intermediate vastus muscle, the nerve to the lateral vastus muscle, the anterior branch of the obturator nerve, the recurrent peroneal nerve, and the lateral retinacular nerve.

Study justification:

Post-knee arthroplasty pain remains an unresolved problem, with various techniques applied to different anatomical targets yielding inconsistent results. To date, no studies have addressed post-knee arthroplasty pain through the application of thermal radiofrequency on sensory branches of the femoral nerve, namely the infrapatellar branch of the saphenous nerve, nerve to the medial vastus muscle, nerve to the intermediate vastus muscle, and nerve to the lateral vastus muscle guided by ultrasound.