Contribution of posture to the maintenance of anal continence
The anorectal angle (ARA) is believed to provide one of the most important contributions to anal continence. The normal resting angle is approx. 90°, but the erect position may modify the ARA and other parameters usually considered in a proctometrogram. We compared the proctometrogram in different postures to elucidate the role of changes in the ARA in maintaining fecal continence. Sixty-three patients with constipation underwent static proctography. Variations in the ARA, perineal descent, puborectalis muscle length, and pubococcygeal distance were determined during resting, squeezing, and pushing with the patient in the Sims' position (SP); further evaluations used radiographs in resting position but with straight legs, in erect and sitting positions. The resting mean ARA was 95.3±15° in SP and 79.8±14° standing erect; the latter value was also significantly less during squeezing (84±11°). The mean ARA during pushing was 118±16°. A systematic and statistically significant difference in the mean resting ARA was demonstrated using the baseline of the rectal shape instead of the major rectal axis when measuring the anorectal angle. When sitting on a toilet, the mean resting ARA was significantly wider than in SP. The length of the puborectalis sling at rest did not change but was significantly reduced during squeezing and increased during pushing. The descent of the perineum at rest was near to 0 (–0.089±1.76 cm) in SP and significantly less when standing (–0.65±1.9 cm) and during squeezing (–0.97±1.7 cm). Perineal descent during pushing was +2.94±2.2 cm. The mean pubococcygeal distance did not change significantly in SP and in the erect position. The erect position thus contributes significantly to the maintenance of fecal continence by sharpening the ARA. This effect is stronger than any active contraction of the puborectalis muscle and is not related to shortening of the puborectalis sling but is secondary to lifting of the pelvic floor.