Anatomic Basis to the Ultrasound-Guided Approach for Saphenous Nerve Blockade

BACKGROUND AND OBJECTIVES: Successful blockade of the saphenous nerve using surface landmarks can be challenging. We evaluated the anatomic basis of performing a saphenous nerve block with ultrasound (US) using its relationship to the saphenous branch of descending genicular artery, sartorius muscle, and the adductor hiatus as defined by cadaveric measurements. METHODS: Using a total of 9 cadaveric knee dissections, the saphenous nerve and its relationship to the saphenous branch of the descending genicular artery (SBDGA) were examined. The distances from the patella to the distal end of the adductor canal and the bifurcation of the saphenous nerve were recorded. US images of an above-the-knee, subsartorial saphenous nerve block were reviewed. RESULTS: The saphenous nerve coursed with the SBDGA. It exited the adductor canal at a median of 10.25 cm (range, 7.0-11.5 cm) cephalad to the proximal patellar border and traveled closely with the SBDGA. At its bifurcation into the infrapatellar branch and sartorial branch, the saphenous nerve was at its closest approximation to the SBDGA. This point was found to be at a median of 2.7 cm (range, 2.1-3.4 cm) cephalad and a median of 6.6 cm (range, 5.0-9.0 cm) posterior to the proximal and posterior patellar border, respectively. CONCLUSIONS: The US-guided approach for saphenous nerve blockade using its close anatomic relationship to the SBDGA is a feasible alternative to previously described surface landmark-based or US-guided paravenous approaches.