Intraobserver and interobserver measurements of the anorectal angle and perineal descent in defecography

Anorectal angle and perineal descent can be measured either by drawing a line defined by the impression of the puborectalis muscle and the tangential of the posterior rectal wall (Method A) or by drawing a straight line at the level of the posterior rectal wall parallel to the central longitudinal axis of the rectum (Method B). The aim of this study was to assess the reproducibility of measuring anorectal angle and perineal descent by two different methods according to intraobserver and interobserver measurement and to evaluate which method yields more consistent results.

Five physicians who have had an average of 1.3 years (range, 6 months to 1.5 years) experience in defecographic measurement drew both lines on 63 randomly selected defecographic films and measured anorectal angle and perineal descent by the two methods. The defecographic parameters were measured twice by each observer during a three-week interval. To avoid potential bias, one physician who did not participate in either measurement of perineal descent or anorectal angle performed all data collection. Intraobserver and interobserver agreement was quantified using Shrout and Fleiss intraclass correlation coefficients.

The mean and range of intraclass correlation coefficients for intraobserver agreement of measuring anorectal angle and perineal descent by Method A were 0.71 (0.6-0.78) and 0.89 (0.74-0.97), respectively, whereas with Method B the coefficients were 0.81 (0.73-0.89) and 0.93 (0.89-0.99), respectively. Regarding the interobserver agreement of the five observers, the mean coefficients for measurement of both anorectal angle and perineal descent by both methods showed similar agreement levels (0.88 and 0.98 by Method A and 0.89 and 0.97 by Method B). The mean (+/- standard deviation) values of anorectal angle and perineal descent found by Method B were significantly larger than those found by Method A (103.3 degrees +/- 19.6 and 6.56+/-3.20 cm and 91.1 degrees +/- 25.6 and 5.64+/-3.42 cm, respectively; P<0.001).

Intraobserver and interobserver intraclass correlation coefficients of anorectal angle and perineal descent, which were measured by both methods, were more than 0.60, indicating that both methods are reliable and consistent for measurement of anorectal angle and perineal descent. However, centers should consistently use the same line for measurement of anorectal angle and perineal descent because of the statistically significant differences between the two methods and the possibility of inconsistent results.