The incidence of lumbar ligamentum flavum midline gaps

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 ligamenturn flavurn. 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 flavurn 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 ligamenturn flavurn midline gaps. Gaps in the lumbar ligamenturn flavurn are most frequent between L1 and L2 but are more rare below this level. When using the midline approach, the ligamenturn flavum may not impede entering the epidural space in all patients.