[Skin-epidural distance in human lumbar region]

To clarify factors that determine the distance between skin and epidural space we analyzed the relationship between distance and factors such as age, sex, height, weight and Broca index using multivariate analysis. Epidural tap was performed in 100 adult patients. Distance was estimated by subtracting the length of needle outside the body from the total length of a Touhy needle. The distance at L3-L4 was significantly longer than that at Th12-L1 and at L1-L2 (P less than 0.05). The distance in male was significantly longer than that in nonpregnant female (P less than 0.05). There was no significantly different distance between pregnant and nonpregnant female. There were good correlations between the distance versus height, weight and Broca index, respectively r = 0.343, r = 0.599, r = 0.328 (P less than 0.05). In this multivariate analysis the first principal component was the site, the second one was the Broca index, the third one was age and the fourth one was height. The distance tended to increase in proportion to aging in this analysis. We conclude that the skin-epidural distance is strongly influenced by the site of puncture and Broca index, but not influenced by pregnancy.