Effects of different defecation angles on imaging, pelvic floor morphology and anorectal dynamics during defecation in patients with functional constipation

[Objectives] To investigate the effects of different defecation angles on imaging, pelvic floor morphology and anorectal dynamics during defecation in patients with functional constipation. [Methods] Eighty-four patients with functional constipation admitted to Handan Central Hospital from January 2021 to March 2023 were selected as the study objects, and were divided into a sitting defecation group (using a toilet with a defecation angle of 90°, n＝28), a slight squatting group (defecation angle of 60°~90°, n＝28) and an Asian squatting group (defecation angle of 30°~60°, n＝28) according to random number table method. Imaging indicators (perineal descent and anorectal angle during resting and defecating phases), pelvic floor morphological indicators (puborectal muscle thickness during resting, defecating, and lifting phases, and the difference in puborectal muscle thickness between resting and defecating phases), and anorectal dynamics indicators (maximum squeeze pressure [MSP], anal resting pressure [ARP], first rectal sensation [FRS], and rectal maximum tolerance volume [RMTV]) were compared among the three groups. [Results] Significant differences were observed in perineal descent and anorectal angle during both resting and defecating phases among the three groups (P<0.05). Specifically, the Asian squatting group had greater perineal descent and anorectal angle than the sitting defecation and slight squatting groups, and the slight squatting group had greater perineal descent and anorectal angle than the sitting defecation group (P<0.05). There were no significant differences in puborectal muscle thickness during resting and lifting phases among the three groups (P>0.05), but significant differences were observed during the defecating phase (P<0.05). Significant differences were also noted in the difference of puborectal muscle thickness between resting and defecating phases among the three groups (P<0.05). The Asian squatting group had thinner puborectal muscle during defecating and a smaller difference in puborectal muscle thickness between resting and defecating phases compared to the sitting defecation and slight squatting groups, and the slight squatting group had smaller values compared to the sitting defecation group (P<0.05). Significant differences were found in MSP, ARP, FRS, and RMTV among the three groups(P<0.05). Specifically, the Asian squatting group had higher MSP and ARP and lower FRS and RMTV compared to the sitting defecation and slight squatting groups, and the slight squatting group had higher MSP and ARP and lower FRS and RMTV compared to the sitting defecation group (P<0.05). [Conclusion] Compared with sitting defecation, adopting a squatting position, especially the Asian squatting position, increases perineal descent and anorectal angle, reduces puborectal muscle thickness during defecating phase, narrows the difference in puborectal muscle thickness between resting and defecating phases, improves anal sphincter function, and exhibits advantages in enhancing rectal sensitivity and lowering rectal tolerance thresholds.