Obstetrical Anal Sphincter Injuries (OASIS) are severe perineal lacerations that predispose to development of anorectal symptoms with significant maternal morbidity that compromise women’s quality of life. Endoanal ultrasound (EAUS) is the gold standard for morphological assessment of the anal sphincter complex. It is used to assess the anal sphincter integrity and detect any persistent anal sphincter defects post repair. 

The purpose of this study was to determine correlation between EAUS findings and anorectal symptoms in women after primary OASIS repair; to determine incidence of residual anal sphincter defects on EAUS after primary OASIS repair; and to determine the rate of clinical overdiagnosis of OASIS.

A retrospective cohort study was conducted for all women with singleton vaginal deliveries who had a primary repair of OASIS and attended the Postpartum Perineal Clinic at a large tertiary care centre between July 1st 2017 and December 31st 2020. Exclusion criteria consisted of women who had EAUS outside the institution, did not undergo EAUS, rectovaginal fistula, or had incomplete data. This study was approved by the Research Ethics Board. Records were reviewed for baseline characteristics, risk factors for OASIS, severity of anorectal symptoms based on St. Mark’s Incontinence Score (SMIS), and findings on EAUS. Data was analyzed using descriptive statistics. Pearson correlation coefficient was used to assess correlation between anorectal symptoms and EAUS findings.

A total of 330 participants with clinical diagnosis of OASIS met the inclusion criteria. From these participants, 156 (47.3%) had sonographic evidence of OASIS on EAUS. The rate of overdiagnosis was 52.7%. A 3rd degree tear was identified in 126 (38.2%) participants. Of these, 60 (18.2%) participants had 3a perineal tear, while 39 (11.8%) participants had 3b perineal tear, and 27 (8.2%) participants had 3c perineal tear. Fourth degree tear was identified in 30 (9.1%) participants. In participants with sonographic evidence of OASIS on EAUS, there was a statistically significant weak positive correlation (r= .3723) between the size of the residual defect of external anal sphincter (EAS) and SMIS (p<.0001). There was also a statistically significant weak positive correlation (r=.3122) between the size of residual defect of the internal anal sphincter (IAS) and SMIS (p=.0180). Residual defect in the anorectal sphincter complex >1 hour was present in 82 (65.1%) participants with 3rd degree tear and 26 (86.7%) participants with 4th degree tear.

This study demonstrates that the size of residual defect of EAS and IAS have a weak positive correlation with anorectal symptoms, emphasizing the importance of EAUS for counselling about subsequent mode of delivery.

The results of this study emphasize the importance of accurate diagnosis and adequate primary OASIS repair.

Continence 2S2 (2022) 100379
DOI: 10.1016/j.cont.2022.100379