Reliability of clinical examination for the assessment of obstetric anal sphincter injuries. A comparative study with 3D endoanal ultrasonography

Objective: Anal incontinence (AI) affects up to 40% of women who sustained obstetric anal sphincter injuries (OASIs) due to persistent defects after primary repair or undiagnosed lesions. Aim of our research was to assess the reliability of clinical assessment of OASIs at the delivery as compared to three-dimensional endoanal ultrasonography (3D-EAUS).

Methods: An observational prospective study was conducted between December 2015 and December 2022. Consecutive women with clinically diagnosed OASIs at the delivery were evaluated by 3D-EAUS two months post-partum. The primary aim was to evaluate the agreement between clinical and ultrasonographic assessment. The secondary aim was to investigate the correlation between ultrasound findings (grade of OASIs and anterior thickness of the external anal sphincter - EAS) and the severity of AI symptoms.

Results: One hundred and sixty women were enrolled, median age 33.6 years (range 19-44; IQR, 30-37). Ninety-eight (61 %) were primiparous and sixty-two (39 %) were multiparous. In one hundred and thirty-seven cases (86 %) there was a perfect agreement between the clinical and ultrasonographic classification of OASIs. Twenty-three women (14 %) were clinically over-staged (17 % of cases) or under-staged (83 % of cases). The agreement between clinical assessment and 3D-EAUS was higher for OASIs grade 3a and 4 than for OASIs grade 3b and 3c (Fisher's test, P < 0.001). Similar findings were found after controlling for age, time interval between clinical evaluation and 3D-EAUS, number of previous deliveries and EAS thickness (R-squared = 0.674). The median anterior thickness of the EAS was 10.4 mm (range 7.2-13.6). The thickness did not correlate to the severity of OASIs (P = 0.215) but it positively correlated with the severity of incontinence symptoms (P < 0.001).

Conclusion: The agreement between clinical and ultrasonographic assessment was high for grade 3a and 4 OASIs. In case of uncertainty, clinical evaluation tended to underestimate the severity of sphincter lesions. The anterior thickness of the EAS was positively correlated with the severity of incontinence symptoms.