Fig. 2. Distribution of the vertebral levels in segments at which the conus medullaris, Tuffier's line, and dural sac cross. The segmental levels where the spinal cord ends, the Tuffier's line crosses, and the dural sac ends followed normal distribution, respectively. Each vertebra and intervertebral space was divided into four segments: upper (U), middle (M), and lower (L) thirds of the vertebral body, and the intervertebral space. L1–5 = lumbar vertebra, S = sacrum, T = thoracic vertebra.