While performing a lumbar puncture, a snap is felt just before entering into the epidural space. This is due to piercing of which structure?

Ans. a. Ligamentum flava (Ref: Gray's 40/e p729, Snell's 9/e p705)While performing a lumbar puncture, a snap is felt just before entering into the epidural space. This is due to piercing of ligamentum flava.Lumbar PunctureThe depth to which the needle will have to pass varies from 2.5 cm or less in a child to as much as 10 cm in obese adults.In caudal anesthesia, needle pierces skin & fascia & sacrococcygeal membrane that fills in the sacral hiatus.The membrane is formed of dense fibrous tissue & represents fused supraspinous & interspinous ligaments as well as ligamentum flavum. A distinct feeling of 'give' is felt when the ligament is penetratedQ.During lumbar puncture, the needle passes through the following anatomic structures before it enters the subarachnoid space:SkinQSubcutaneous tissueQSupraspinous ligamentQInterspinous ligamentQLigamentum flavumQDura materQArachnoid materQ