The L3-4 inter-laminar space will be selected as the target for puncture, and in the longitudinal direction, 1.0-1.5cm will be opened beside the upper edge of the spinous process (tip) of the lower vertebra as the entry point. The lumbar puncture needle will be inserted vertically along the axis of the anesthesia needle. The puncture path will be maintained completely perpendicular to the skin until the needle reached the PLTLF (posterior layer of the thoracolumbar fascia), where some resistance will be felt. The puncture direction is adjusted as needed. The tip of the needle will be tilted 20±10° in the sagittal direction and 15±5° inward such that the tip will point at the midpoint of the spinal canal. After the needle reaches the PLTLF, it will be further inserted 3-7 cm.

Puncture will be performed on the posterior median line near the midpoint of the L3-4 Space of spinous process. The lumbar puncture needle will be inserted vertically along the axis of the anesthesia needle, or the tip of the needle will be tilted 15° in the sagittal direction toward the head, so that the needle path is parallel to the space of spinous process.

Computer-Assisted Paramedian Approach Technique

A successful puncture was defined as the presence of CSF outflow from the puncture needle. The number of needle insertion attempts was determined by the number of times the puncture needle was inserted into the target area.

The parameters will measure the success rate of puncture in one attempt, the success rate of puncture within three attempts and the success rate of puncture within six attempts.

The time taken to locate and mark the patient, defined as the duration from the beginning of positioning till the insertion of the anaesthetic needle.