Femoral nerve “sheath” for inguinal paravascular lumbar plexus block is not found in human cadavers

Abstract

Study Objective: To determine if a femoral nerve sheath capable of conveying local anesthetic to the lumbar plexus and the obturator nerve exists in human cadavers. Design: Injection of methylene blue dye into the femoral nerves of human cadavers followed by dissection and observation of dye distribution. Setting: University medical center pathology department autopsy room. Patients: Six fresh adult cadavers about to undergo postmortem examination. Interventions: Both femoral nerves of six fresh cadavers were injected with either 20 ml or 40 ml of dye. The abdomen was opened and distribution of the dye was observed. Measurements and Main Results: In all of the cadavers studied there was no evidence of a femoral nerve sheath capable of conveying methylene blue dye to the lumbar plexus. Both 20 ml and 40 ml of dye injected into the femoral nerve failed to reach the lumbar plexus or the obturator nerve. When 40 ml of dye was injected it always stained the femoral nerves, it usually stained the lateral femoral cutaneous nerves, but it never stained the obturator nerves. Conclusions: A femoral nerve sheath capable of conveying a solution to the cadaver lumbar plexus does not exist in human cadavers. Dye injected into the cadaver femoral nerve does not reach either the lumbar plexus or the obturator nerve. When 40 ml of methylene blue dye is injected into the cadaver femoral nerve, some dye usually diffuses under the iliacus muscle fascia to the lateral femoral cutaneous nerve. This study indicates that in patients the “3-in-1 block” always blocks the femoral nerve, it usually blocks the lateral femoral cutaneous nerve, but it probably does not block the lumbar plexus or the obturator nerve.