Anatomy and Anaesthesia of the Lumbar Somatic Plexus

Abstract

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.

The Malignant Psoas Syndrome Revisited: Case Report, Mechanisms, and Current Therapeutic Options

“…Sensory branches supply the anteromedial aspect of the thigh. 9 These relationships reflected the dermatomal pattern of hyperesthesia seen in our case.…”

A Description of the Spread of Injectate After Psoas Compartment Block Using Magnetic Resonance Imaging

“…12 The lumbar plexus lies within the psoas muscle in a fascial plane that separates the muscle into anterior and posterior parts. 2,3 The lumbar nerve roots (L1-4) enter the psoas muscle and form lumbar nerve branches and the terminal nerves. 1,2 The L1 and L1-2 nerve roots give rise to the iliohypogastric/ilioinguinal nerves and genitofemoral nerve, respectively.…”

“…1,2 The L1 and L1-2 nerve roots give rise to the iliohypogastric/ilioinguinal nerves and genitofemoral nerve, respectively. 3 The LFC nerve formed from the L2 or L2-3 nerve roots runs in the fascial plane with the femoral nerve until it leaves the psoas at the L4 or L5 level. 1,3 The femoral nerve arises within the psoas muscle from the posterior divisions of the L2-3 and L4 lumbar branches, usually below the transverse process of L4, and emerges posterolateral to the muscle at a level that ranges from L4 to S1.…”

“…3 The LFC nerve formed from the L2 or L2-3 nerve roots runs in the fascial plane with the femoral nerve until it leaves the psoas at the L4 or L5 level. 1,3 The femoral nerve arises within the psoas muscle from the posterior divisions of the L2-3 and L4 lumbar branches, usually below the transverse process of L4, and emerges posterolateral to the muscle at a level that ranges from L4 to S1. 2,14 The anterior divisions of these branches become the obturator nerve, which lies medial to the femoral and LFC nerves and is often (50% to 60% of cases) found separated from these nerves by a muscular fold and, therefore, outside the fascial plane.…”

“…2 The femoral and LFC nerves, and, more variably, the obturator nerve, run in a fascial plane within the psoas muscle before leaving the muscle at various levels. 1,3 Physical spread of solution after posterior lumbar plexus or psoas compartment block (PCB) is, therefore, most likely to occur within the psoas muscle. 4 Few studies have investigated the physical distribution of injectate after PCB.…”