title: Lumbar plexus and psoas major muscle: not always as expected.
abstract: OBJECTIVE
  Conflicting definitions concerning the exact location of the lumbar plexus have been proposed. The present study was carried out to detect anatomical variants regarding the topographical relation between the lumbar plexus and the psoas major muscle as well as lumbar plexus anatomy at the L4-L5 level.
  
  
  METHODS
  Sixty-three lumbar plexuses from 32 embalmed cadavers were dissected to determine the topographical relation between lumbar plexus and psoas major muscle. At the L4-L5 levels variability in the course of the femoral as well as obturator nerve were described.
  
  
  RESULTS
  The lumbar plexus was situated within the psoas major muscle in 61 of 63 cases. In 2 of 63 cases the entire plexus was localized posterior to the psoas major muscle. In the 61 of 63 cases in which the lumbar plexus was situated within the psoas major muscle, emergence of the individual nerves most often occurred on the posterior or posterolateral surface.
  
  
  CONCLUSIONS
  Our results synthesize contrasting assumptions in previous literature, by demonstrating that both locations of the lumbar plexus may be encountered in clinical practice: within and posterior to the psoas major muscle. However, the latter situation represents a minor variant. At the level of L4-L5 the femoral nerve, showing a remarkable degree of branching, as well as the obturator nerve, were found within the psoas major muscle in the vast majority of specimens.
authors.affiliation: Department of Anesthesiology and Critical Care Medicine, Innsbruck Medical University, Innsbruck, Austria. lukas.kirchmair@uki.at
authors.forename: Lukas
authors.initials: L
authors.lastname: Kirchmair
authors.forename: Philipp
authors.initials: P
authors.lastname: Lirk
authors.forename: Joshua
authors.initials: J
authors.lastname: Colvin
authors.forename: Gottfried
authors.initials: G
authors.lastname: Mitterschiffthaler
authors.forename: Bernhard
authors.initials: B
authors.lastname: Moriggl
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002102:Cadaver; D005260:Female; D005267:Femoral Nerve / Q000033:anatomy & histology; D006801:Humans; D008160:Lumbosacral Plexus / Q000033:anatomy & histology*; D008297:Male; D008875:Middle Aged; D009776:Obturator Nerve / Q000033:anatomy & histology; D016658:Psoas Muscles / Q000033:anatomy & histology*; D015203:Reproducibility of Results