Objective: In the femoral "3-in-1 block", obturator nerve block is routinely unsuccessful. Anatomical studies are not available to explain why blockade of obturator nerve or lumbar plexus does not occur. The aim of this study was to examine the effectiveness of femoral "3-in-1 block" obturator nerve block on a cadaver model.
Materials and methods: Totally, 12 mature adult human cadavers were selected. Methylene blue dye (30 ml) was in-jected under the fascia iliaca in eight cadavers and into the femoral nerve sheath in four cadavers. Careful bilateral dissections were performed following dye injections.
Results: It was seen that the dye did not spread to the medial part of the psoas major muscle and the obturator nerve was not stained with the dye in eight cadavers in whom dye was injected laterally into the femoral sheat. In four ca-davers in whom dye was injected into the femoral nerve sheat, metylene blue spread through fascial layers in the plane under the psoas muscle and stained the obturator nerve just before emerging medially from the fascia psoas. At this point, the obturator nerve pierced the psoas fascia and extended extrafascially in the medial and deep borders of the psoas muscle. In this area, the upper section of the obturator nerve was found also to be stained with the dye.
Conclusion: We concluded that the cause of an unsuccessful obturator nerve block might be the fascial anatomy of this region. The lateral cutaneous femoral nerve and the femoral nerve easily can be blocked in the fascia iliaca com-partment, but the obturator nerve block fails because of its being extrafascial in this region.