Letter to the Editor: Infrapatellar Saphenous Neuralgia After TKA Can Be Improved With Ultrasound-guided Local Treatments

Abstract

To the Editor, We read the retrospective case series conducted by Clendenen and colleagues and appreciate their efforts in exploring a patient population with infrapatellar saphenous neuralgia after TKA [1]. Their research indicates ultrasound-guided injection to the infrapatellar branch of the saphenous nerve is a potential approach for recalcitrant pain following TKA. In their results, the response rate to the injection combining corticosteroid and local anesthesia was 56.3% (9 out of 16). Since there was no comparative group, we are unaware that this advanced approach is superior to conservative treatments like manual exercise or physical therapy. However, a more-than-50% success rate with nerve block draws attention to the neuropathic component in patients with persistent knee pain after TKA. Peripheral and central sensitization could potentially be associated with chronic intractable pain in knee osteoarthritis [2]. Although the present research supports the role of peripheral neuralgia in relentless postarthroplasty knee pain [1], central sensitization might partly account for the patients failing to respond to nerve block. Therefore, oral medication modifying central pain perception can be considered in combination with medication targeting nociceptive pain [3]. Additionally, evaluation tools designed for measuring neuropathic pain, such as the PainDETECT score and the DN4 questionnaire [2], should be implemented to monitor treatment effectiveness. Another concern is the diagnosis for entrapment of the infrapatellar branch of the saphenous nerve, which was made by the response to injection in the present study. The potential segment of nerve entrapment is from the vastoadductor membrane to the medial femoral epicondyle [4]. Whether the entrapped nerves presented with swelling, hypoechogenicity, or hypervascularity is of interest, but this information is lacking in this case series. Besides recording the sonographic images of the affected side, we suggest the authors also compare the nerve echotexture with the asymptomatic side, which is the easiest way to identify nerve damage by ultrasound.