The anthropometric definition of the rectum is highly variable

Purpose: The precise definition of the rectum is essential for localizing colorectal pathology, yet current definitions are nebulous. The objective of this study is to determine the anthropometric definition of common pelvic landmarks in relation to patient characteristics. Methods: Seventy-one patients underwent open proctectomy with intra-operative measurements from the anal verge to various pelvic landmarks, and patient characteristics were evaluated. Analyses were performed using Spearman correlation and Wilcoxon rank sum. Results: The mean landmark distance was dentate line = 1.7 cm (range 0.8–4.0 cm), puborectalis muscle = 4.2 cm (range 2.0–8.0 cm), anterior peritoneal reflection = 13.2 cm (range 8.5–21.0 cm), sacral promontory = 17.9 cm (range 13.0–26.0 cm), and confluence of the taenia = 25.5 cm (range 16.0–44.0 cm). Men had longer mean distances to the dentate line (p = 0.0003), puborectalis muscle (p = 0.03), and anterior peritoneal reflection (p = 0.02). Patient weight significantly correlated with distance to all landmarks except for the confluence of the taenia, which did not correlate with any patient factor. Conclusions: The location of common pelvic landmarks is highly variable. The use of predefined absolute measurements from the anal verge to localize rectal pathology is inaccurate and fails to account for patient variability.