title: The incidence of lumbar ligamentum flavum midline gaps.
abstract: Lumbar epidural anesthesia and analgesia has gained increasing importance in perioperative pain therapy for abdominal and lower limb surgery. The loss-of-resistance technique, used to identify the epidural space, is thought to rely on the penetration of the ligamentum flavum. However, the exact morphology of the ligamentum flavum at different vertebral levels remains controversial. Therefore, in this study, we directly investigated the incidence of lumbar ligamentum flavum midline gaps in embalmed cadavers. Vertebral column specimens were obtained from 45 human cadavers. On each dissected level, ligamentum flavum midline gaps were recorded. The incidence of midline gaps per number of viable specimens at the following levels was: L1-2 = 10 of 45 (22.2%), L2-3 = 5 of 44 (11.4%), L3-4 = 5 of 45 (11.1%), L4-5 = 4 of 43 (9.3%), L5/S1 = 0 of 33 (0%). In conclusion, the present study determined the frequency of lumbar ligamentum flavum midline gaps. Gaps in the lumbar ligamentum flavum are most frequent between L1 and L2 but are more rare below this level. When using the midline approach, the ligamentum flavum may not impede entering the epidural space in all patients.
  
  
  CONCLUSIONS
  The ligamentum flavum is a crucial anatomical landmark for the safe performance of epidural anesthesia. However, the present study demonstrates some failure of the lumbar ligamentum flavum as a landmark. This may mean that, using a midline approach, one cannot always rely on the ligamentum flavum as a perceptible barrier to epidural needle advancement.
authors.affiliation: *Department of Anesthesiology and Critical Care Medicine and the †Institute of Anatomy, Histology, and Embryology, University of Innsbruck, Austria; and ‡Department of Anesthesiology, Medical College of Wisconsin, Milwaukee.
authors.forename: Philipp
authors.initials: P
authors.lastname: Lirk
authors.forename: Bernhard
authors.initials: B
authors.lastname: Moriggl
authors.forename: Joshua
authors.initials: J
authors.lastname: Colvin
authors.forename: Christian
authors.initials: C
authors.lastname: Keller
authors.forename: Lukas
authors.initials: L
authors.lastname: Kirchmair
authors.forename: Josef
authors.initials: J
authors.lastname: Rieder
authors.forename: Christian
authors.initials: C
authors.lastname: Kolbitsch
mesh_terms: D002102:Cadaver; D004824:Epidural Space / Q000033:anatomy & histology; D006801:Humans; D017843:Ligamentum Flavum / Q000033:anatomy & histology*; D015588:Observer Variation