What is the true location of Jacoby's line?

We investigated 60 cadavers to examine the accurate location of conus medullaris, lower end of dura mater, and intercrestal line (Jacoby's line). Jacoby's line was established using the method described by Jacoby GW (1899). Then the intersection of this line and vertical line through the spinous processes was marked by a fine nail. After a laminectomy was performed to expose the spinal cord, spinal level of the conus medullaris, the lower end of dura mater, and Jacoby's line were examined, and marked and recorded these locations of nailing. In 2 of 48 cases (2.1%), Jacoby's line passed through the level superior to 3rd lumber vertebra (L3). The Conus medullaris was at the level beneath L3 in 2 of 57 cases (3.5%). And lower end of dura mater was located beneath the superior margin of S3 in 1 of 28 cases (3.6%). When Jacoby's line is used as a guide-point, the site for subarachnoid puncture is established in the L3-4 interspinous space. But when we consider the risk of spinal cord injury cannot be completely excluded, in case that conus medullaris is located inferior to L3 in 3.5% of cases. Conseqently, it should be important to avoid performing subarachnoid puncture at L2-3 or higher lumbar vertebral level especially in the elderly.