Dissimilar Planes and Approaches with Common Neural Targets - A Cadaveric Evaluation of Three Different Ultrasound-guided Fascial Plane Blocks for Lumbar Plexus Nerves.

Background: The lumbar plexus (LP) is a group of nerves located at the fourth lumbar vertebra level, between the anterior two-thirds and posterior one-thirds of the psoas muscle. In this study, the researchers aimed to investigate the spread of latex in injections of LP, suprainguinal fascia iliaca, and circum-psoas planes to assess the different regional techniques for blocking LP nerves (LPNs). Methods: The study involved performing ultrasound-guided injections of three different colored latexes in six cadavers. The researchers observed and compared the spread of latex in each plane by taking cross sections at the levels of L4, anterior superior iliac spine (ASIS), and sacral foramina (SF). The spread of latex and LPN staining was documented and analyzed through photography. Results: The results showed that the latex spread within the psoas muscle and fascia iliaca plane (FIP) during LP injections, whereas suprainguinal fascia iliaca injections showed latex dissemination in the FIP at both ASIS and SF levels. On the other hand, circum-psoas injections spread beneath the iliopsoas fascia at both levels and medially toward the external iliac vessels. Despite this spread, there was no communication between the three planes, and there was no mixing of latex from the different injections at any level. Conclusion: There are distinct fascial planes, for the three approaches, with no communication between them. While latex diffused from LP plane to FIP, no mixing of dye was observed and also the reverse could not be achieved. These findings suggest that different regional techniques for blocking LPNs have their unique planes of action.