Fig. 4

A Correlation between the lumbar dural sac length (DSL) and peak tactile block level (r = − 0.727, p < 0.0001). B Correlation between the lumbar dural sac surface area (DSA) and peak tactile block level (r = − 0.633, p < 0.0001). C Correlation between the lumbar dural sac volume (DSV) and peak tactile block level (r = − 0.534, p < 0.0001). D Correlation between the lumbar dural sac diameter (DSD) and peak tactile block level (r = − 0.238, p < 0.0001). Although correlation coefficients (r) and P values were calculated using Pearson’s correlation, the linear regression lines are presented in these graphs