SummaryThe anatomy of the lumbar plexus and the various approaches used to perform lumbar plexus blockade are reviewed. A single needle technique for a posterior approach to the plexus at the L , interspace is described. This technique was used bilaterally in six intact cadavers, and the extent of spread of an injected dye was documented photographically during a subsequent detailed dissection of the region. In all cases, dye was confined to the posterior part of the psoas muscle, and tracked down the nerves of the lumbar plexus. No dye was seen anterior to the psoas, around the sympathetic chain, on the sacral plexus or in the extradural or subarachnoid spaces. Further studies in patients with needle position and drug dispositon being confirmed using computerised tomography and X ray scanning were in agreement with the results observed in the cadavers. This technique represents a simple approach to the lumbar plexus which does not require needle localisation by X ray screening. Key wordsAnaesthesia, regionat lumbar plexus block.Regional techniques for anaesthesia and analgesia of the lower limb have been historically regarded as more difficult than those for the upper limb. It has been assumed that the depth of the lumbar plexus and the distance between its roots make it difficult to locate, necessitating multiple procedures and resulting in a high failure rate [1,2]. Despite these difficulties a variety of techniques for lumbar plexus blockade have been described for use in the management of chronic pain, and in the provision of surgical analgesia for adults and children [3].Both posterior and anterior approaches to the plexus have been described: (a) paravertebral approaches using either multiple injections at each root of the plexus Although it has been used for many years, it has never been published, and no previous anatomical studies have been undertaken.between the psoas and quadratus lumborum muscles, (which contain part of the lumbar plexus as it emerges from the lateral side of psoas major) or into the posterior part of the psoas muscle at this level [5-71; (d) anterior approaches where the needle is placed lateral to the femoral artery in the inguinal region (inguinal paravascular technique [8]) or immediately behind the fascia iliaca at a point two-thirds laterally along the inguinal ligament [9].In recent assessments of the extent of sensory and motor blockade achieved with different approaches to the lumbar plexus, the posterior approaches were found to result in a more extensive block than were the anterior approaches [5,9]. Although the posterior approaches are likely to result in superior lumbar plexus anaesthesia, they may be technically more difficult and may be associated with inadvertent extradural or subarachnoid block, particularly if large volumes of local anaesthetic are used [5,10].The present study was performed to assess the location and spread of a dye injected via a posterior approach without X ray control to the lumbar plexus at the LZT3 interspace. MethodsHospital ethics committe...

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