Background and Objectives Saphenous nerve blocks can be technically challenging. Recently described ultrasound techniques have improved the success rate of saphenous nerve blocks, but randomized controlled trials comparing these ultrasound-guided techniques are lacking. We compared 2 common ultrasound-guided approaches for saphenous nerve block: saphenous nerve block at the adductor canal (ACSNB) versus block by the distal transsartorial (DTSNB) approach.

Methods Patients received either ACSNB or DTSNB in this prospective, randomized, blinded, noninferiority clinical trial. The primary objective was to show the noninferiority of ACSNB to DTSNB in terms of block success. Secondary outcome measures were time required to perform the block, time to onset of successful block, and the visibility of the nerve using ultrasound.

Results One hundred twenty patients were randomized to receive DTSNB (n = 62) or ACSNB (n = 58). There were 9 failures in the DTSNB group (85% success) and no failures in the ACSNB group (100% success), 90% confidence interval of difference in success rates (DTSNB - ACSNB) was −0.195 to −0.031. Given that the upper confidence bound (−3.1%) was less than 10%, the success rate of ACSNB was noninferior to DTSNB. After satisfying noninferiority and observing a greater success rate of ACSNB compared with DTSNB, we also determined that ACSNB was superior to DTSNB (P = 0.003). The median time to success was significantly less for the ACSNB group: 9 minutes versus 3 minutes (P < 0.001). The grade of the ultrasound image, as judged by the provider, was significantly better in the ACSNB group (P = 0.001).

Conclusions Ultrasound-guided block of the saphenous nerve at the adductor canal is not only noninferior but also superior to block at the distal transsartorial level in terms of success rate, with additional advantages of faster block onset time and better nerve visibility under ultrasound.