The 'snap' felt before entering the epidural space represents passage through which ligament?

The 'snap' felt before entering the epidural space represents passage through which ligament?

• A. Anterior longitudinal ligaments
• B. Posterior longitudinal ligaments
• C. Ligamentum flavum
• D. Supraspinous ligament

Answer: (C)

When accessing the epidural space, the needle must pass through several posterior spinal ligaments before entering the space itself. The ligament that forms the tough, elastic posterior boundary you must penetrate to reach the epidural space is the ligamentum flavum. Feeling a distinct resistance that suddenly gives way—the so-called “snap” or crack—signals that the needle has pierced this ligament and entered the epidural space. After this, the familiar loss of resistance to injection helps confirm placement. The other ligaments mentioned aren’t the structures breached at this moment. The anterior longitudinal ligament runs along the front of the spine, far from the midline posterior approach. The posterior longitudinal ligament lies inside the spinal canal along the posterior aspect of the vertebral bodies, not in the superficial tract of an epidural needle. The supraspinous ligament is more superficial, spanning the tips of the spinous processes, and while you pass through it along the way, the characteristic tactile event most closely associated with entering the epidural space is the perforation of the ligamentum flavum.

When accessing the epidural space, the needle must pass through several posterior spinal ligaments before entering the space itself. The ligament that forms the tough, elastic posterior boundary you must penetrate to reach the epidural space is the ligamentum flavum. Feeling a distinct resistance that suddenly gives way—the so-called “snap” or crack—signals that the needle has pierced this ligament and entered the epidural space. After this, the familiar loss of resistance to injection helps confirm placement.

The other ligaments mentioned aren’t the structures breached at this moment. The anterior longitudinal ligament runs along the front of the spine, far from the midline posterior approach. The posterior longitudinal ligament lies inside the spinal canal along the posterior aspect of the vertebral bodies, not in the superficial tract of an epidural needle. The supraspinous ligament is more superficial, spanning the tips of the spinous processes, and while you pass through it along the way, the characteristic tactile event most closely associated with entering the epidural space is the perforation of the ligamentum flavum.