Computed tomographic study of lumbar (L3-4) epidural depth and its relationship to physical measurements in young adult men.

Abstract

This study was performed to devise a method for predicting epidural depth more accurately with a variety of physical measurements not previously studied. Computed tomography was used to accurately measure the L3-4 epidural depth. The inclusion criteria were restricted to healthy men, 20-25 years of age, in order to rule out the influences of age and sex. Significant correlations with depth from skin to the center of the "triangular" posterior epidural space (Sk-Ep) were found for waist circumference, waist circumference/height ratio, body mass index (BMI), weight/height ratio, weight/neck circumference ratio, and weight. The depth from the supraspinous ligament to the center of the posterior epidural space (SI-Ep) did not correlate with any physical measurements. However, Sk-Sl, which equals Sk-Ep minus Sl-Ep (ie, the depth from the skin to the supraspinous ligament) correlated with waist circumference/height ratio, waist circumference, BMI, and weight/height ratio. Addition of the physical parameters such as waist circumference/neck circumference ratio or BMI results in a higher predictive value for epidural depth than use of more traditional physical parameters such as weight/height ratio and/or weight only. The value of Sl-Ep is independent of any physical parameters. Thus, the significant correlation between the physical measurements and the epidural depth seems to be due only to obesity-related factors.