Ultrasound-guided saphenous nerve block – within versus distal to the adductor canal: a proof-of-principle randomized trial

Purpose Reliable saphenous nerve blockade is a desirable complement to popliteal sciatic nerve blockade for foot and ankle surgery. We compared two promising ultrasound-guided techniques, the supine adductor canal (AC) technique and the prone peri-saphenous branch of the descending genicular artery (Peri-SBDGA) technique, using 8 mL of 2% lidocaine with epinephrine 1:400,000. Methods Following Research Ethics Board approval, we conducted a randomized single-blinded parallel-group trial in 102 patients undergoing foot and ankle surgery at a single centre. The primary endpoint was saphenous nerve ease of visualization (0 = not visible; 1 = visible with difficulty; and 2 = easily visible). Other endpoints included vascular landmark visualization (0 = not visible; 1= visible with colour flow Doppler; 2 = visible without colour flow Doppler), block success, onset, and complications. Results Ninety-one patients were eligible for analysis. Saphenous nerve visibility was not different between the groups (visibility score = 2: AC group, n = 24/49 [49%] vs Peri-SBDGA group, 20/42 [48%]; P = 1.00). Vascular landmark visibility was better in the AC group than in the Peri-SBDGA group (visibility score = 2: 41/49 [84%] vs 25/42 [60%], respectively; P = 0.018). Block success rates were similar (AC group, 41/49 [84%] vs Peri-SBDGA group, 34/42 [81%]; P = 0.79), as were median [interquartile range] onset times (AC group, 5 [5-10] min vs Peri-SBDGA group, 8 [5-11] min; P = 0.38). Conclusion In this randomized trial, we found no differences in nerve visibility, block success rate, or onset between the AC and Peri-SBDGA techniques of ultrasound-guided saphenous nerve blockade, although the former technique provided superior vascular landmark visibility. Neither technique produced a sufficiently high success rate to provide reliable surgical anesthesia per se .