Please confirm that an ethics committee approval has been applied for or granted: Not relevant

Background and Aims Adductor canal block (ACB) is an effective analgesic technique for lower limb surgeries. Anatomic studies on injectate spread yield mixed results. Here, we assess dye spread at three distinct adductor canal locations.

Methods An observational cadaveric study was conducted. Twelve lower limbs from fresh unembalmed cadavers were studied. An ultrasound-guided adductor canal block with 20 ml of methylene blue was performed in each limb in one of three locations that was defined according to the location of femoral artery (FA): Medial (proximal adductor canal), inferior (mid-adductor canal), and lateral (distal adductor canal) to the mid-point of the sartorius muscle (SM). Nine limbs (three of each injection location) were dissected to asses spread location. The 3 other specimens were sectioned in coronal slices for further anatomical examination. We hypothesized that proximal (femoral triangle, femoral nerve) and distal (popliteal fosa) spread would differ according to the injection location.

Results Regardless of injection location, staining was observed in adductor canal in all specimens. In the proximal injection, 3 specimens (75%) had staining of the femoral nerve, without distal spread. In the mid-location, no proximal nor distal spread was noted. In the distal location, in 1 specimen (25%) spread reached the popliteal fossa, while in 2 cases (50%) it reached the adductor hiatus without staining the popliteal fossa. No femoral triangle spread was observed in the distal location.

Conclusions An ACB performed in the mid-location (fermoral artery inferior to the sartorius muscle) does not result in proximal nor distal spread.