Fig. 4. Correlation between age and segmental levels at which the conus medullaris, Tuffier's line, or dural sac cross. Position of the conus medullaris was lower with age (r =−0.137, P < 0.001); position of Tuffier's line was higher with age (r = 0.243, P < 0.001). The vertical distance between the conus medullaris and Tuffier's line decreased with age (r =−0.286, P < 0.001), and the position of the dural sac was constant regardless of age. Numbers of the segmental level of vertebra or intervertebral space are: 5 = lower portion of S2, 10 = midportion of S1, 15 = upper portion of L5, 20 = L3L4 intervertebral space, 25 = lower portion of L2, 30 = midportion of L1, and 35 = upper portion of T12.