Abstract： Objective To investigate the limiting effect of pelvic diameters on the technical difficulty of total mesorectal excision (TME) for rectal cancer by computed tomography pelvimetry.Methods From January 2009 to January 2011,69 patients with rectal cancer underwent TME in the Department of Proctology at the Changhai Hospital in Shanghai.There were 55 males and 14 females.Using three dimensional reconstruction software,pelvic dimensions of rectal cancer patients were measured based on pelvic MDCT thin-slice computed tomography.All the patients were measured for 15 pelvic parameters,including the length of pelvic inlet,the length of pubic symphysis,the interspinous distance,the distance from sacral promontory to tip of coccyx,etc.All the procedures were open surgery,including anterior resection (n=19),low anterior resection and ileostomy (n=29) and abdominal perineal resection (n=21).Duration of the operation and blood loss at surgery were recorded as evaluation indicators of the technical difficulty of total mesorectal excision.By univariate analysis significant pelvic parameters were selected.Multiple regression analysis was used to investigate the relationship between pelvic parameters and blood loss or duration of operation.Results The mean operative time was (139.9±32.4) min and the mean intraoperative blood loss was (228.8±150.6) ml.Multivariate analysis showed that the interspinous distance,the length of pelvic inlet,the distance from sacral promontory to the tip of coccyx were the main factors affecting the operation time,and that the length of pubic symphysis and the distance from sacral promontory to the tip of coccyx were the main factors affecting the amount of blood loss (all P＜0.05).Among the 3 procedures,the multivariate analysis for low anterior resection appeared to be most valuable,in which operative time was associated with the distance from sacral promontory to the tip of coccyx and the interspinous distance (adjusted coefficient of determination of the regression equation,Rc2=0.460,P=0.003).Factors associated with intraoperative blood loss were the length of pelvic inlet,the distance from sacral promontory to the tip of coccyx,and the sacrum-pubis angle (Rc2=0.358,P=0.022).Comprehensive analysis of the measurement parameters showed that the ratio between the length of pelvic inlet and the distance from sacral promontory to the tip of coccyx was associated with the operative time and blood loss.This ratio was significantly higher in female patients than that in males.In females with a ratio greater than 1,the operative time was significantly shorter (P=0.050),and the intraoperative blood loss was significantly less in males with a ratio greater than 0.9 (P=0.021).Conclusions Operative time and intraoperative blood loss for total mesorectal excision are more favorable in patients with a wide and shadow pelvis.Surgical difficulty is increased in deep and narrow pelvis or those with major sacrum curvature.The difficulty of total mesorectal excision procedure can be predicted by measuring the length of pelvic inlet and the distance from sacral promontory to the tip of coccyx.