Correlations of obstetric anal sphincter injury (OASIS) grade, specific symptoms of anal incontinence, and measurements by endoanal and transperineal ultrasound

Purpose: The aim of the study was to investigate the association between the initial grade of obstetrical anal sphincter injury (OASIS), and Wexner score parameters, with ultrasonographic findings by endoanal ultrasound (EAUS, golden standard) and transperineal ultrasound (TPUS) 6 months post-partum. Methods: Fifty-nine women after primary repair of OASIS were included at Helsingborg Hospital, Sweden, 2016–2017. Six months post-partum the women filled in a questionnaire regarding symptoms of anal incontinence by the Wexner score and were scanned with EAUS and TPUS (resting state and contracting state) for classification of the residual defect by a modified Starck score. Results: Correlations were found between the OASIS grade and residual defects; length (r_s = 0.41, P = 0.003), depth (r_s = 0.38, P = 0.006) and angle (r_s = 0.40, P = 0.004) of the external anal sphincter (EAS) measured with TPUS in resting state. Using EAUS, correlation between OASIS grade and EAS depth (r_s = 0.35, P = 0.007) and angle (r_s = 0.37, P = 0.004) were similar, but there was no correlation with length (r_s = 0.20, P = 0.14). Between incontinence to gas and the angle of the residual defect in the IAS using TPUS in resting state, correlation was moderate (r_s = 0.42, P = 0.003). Regarding incontinence to liquid stool, measurements by TPUS in resting state of EAS residual defect depth (r_s = 0.46, P < 0.001) and angle (r_s = 0.44, P = 0.001) also correlated moderately. Both corresponding correlations using EAUS were weaker. Conclusion: Defects measured with EAUS and TPUS six months post-partum correlated to initial OASIS grade and symptoms of anal incontinence. Specific symptoms correlated with specific anatomical defects, and TPUS was not an inferior method to EAUS.