Anatomy and anaesthesia of the lumbar somatic plexus.

Cadaveric dissection demonstrated the lumbar plexus to lie within the substance of psoas major, with the major branches of the lumbar plexus emerging into the psoas compartment adjacent to the L5 vertebra. Within psoas major, the lateral femoral cutaneous and femoral nerves were separated from the obturator nerve by a muscular fold in 36 of 60 plexuses. Anatomical variations were common, with the accessory obturator nerve being identified in 12 per cent of plexuses. All previously described lumbar plexus block approaches positioned the needle within close proximity to the lumbar plexus. Modifications to these approaches may increase efficacy and reduce complication rates.