Feasibility and efficacy of ultrasound-guided block of the saphenous nerve in the adductor canal

Abstract

Background and objectives: Saphenous nerve (SN) block can be technically challenging because it is a small and exclusively sensory nerve. Traditional techniques using surface landmarks and nerve stimulation are limited by inconsistent success rates. This descriptive prospective study assesses the feasibility of performing an ultrasound-guided SN block in the distal thigh.

Methods: After the research ethics board's approval and written informed consent, 20 patients undergoing ankle or foot surgery underwent ultrasonography of the medial aspect of the thigh to identify the SN in the adductor canal, as it lies adjacent to the femoral artery (FA), deep to the sartorius muscle. An insulated needle was advanced in plane under real-time guidance toward the nerve. After attempting to elicit paresthesia with nerve stimulation, 2% lidocaine with 1:200,000 epinephrine (5 mL) and 0.5% bupivacaine (5 mL) were injected around the SN.

Results: The SN was identified in all patients, most frequently in an anteromedial position relative to the FA, at a depth of 2.7 +/- 0.6 cm and 12.7 +/- 2.2 cm proximal to the knee joint. Complete anesthesia in the SN distribution developed in all patients by 25 mins after injection.

Conclusions: In this small descriptive study, ultrasound-guided SN block in the adductor canal was technically simple and reliable, providing consistent nerve identification and block success.