Levator ani muscle morphology and function in women with obstetric anal sphincter injury

OBJECTIVES: To estimate the prevalence and explore risk factors of levator ani muscle injury in women with clinically diagnosed obstetric anal sphincter injuries (OASIs). Secondly, we aimed to assess the association between levator injury and pelvic floor muscle contraction, anal incontinence (AI) and urinary incontinence (UI) in women with OASIs. METHODS: Cross-sectional study of 250 women with OASIs, recruited from 2013 until 2015 in a tertiary referral centre at Croydon University Hospital, UK. AI symptoms were assessed using the modified St Mark's Incontinence Score and UI using the International Consultation on Incontinence modular Questionnaire for Urinary Incontinence - Short Form. All women underwent 3D/4D transperineal ultrasound at rest and at maximum pelvic floor contraction. Major levator injury was defined as a uni-or bilateral defect in all three central slices using tomographic ultrasound imaging. Muscle contraction was assessed using the Modified Oxford Scale (MOS) and measured on ultrasound as the proportional change of the anteroposterior (AP) levator hiatal diameter between rest and contraction. We used multivariable logistic regression to study risk factors for levator injury. Multivariable ANCOVA and Mann-Whitney U test were used to study difference in contraction and symptoms between women with intact and injured levator. RESULTS: 29.4% of women who previously sustained OASIs were found to have major levator injury. This was 23.6% after normal vaginal delivery, and 40.2% after operative vaginal delivery; adjusted odds ratio 4.1 (95% CI 1.4-11.9), p=0.01. Levator injury was associated with weaker pelvic floor muscle contraction; adjusted mean difference for proportional change in AP difference 4.2 (95% CI 1.7 - 6.7) and MOS 0.5 (95% CI 0.2-0.9), p< 0.01. Symptoms were similar for women with intact and injured levator muscle. CONCLUSIONS: Operative vaginal delivery was a risk factor for levator injury in women with OASIs, and levator injury was associated with a weaker pelvic floor muscle contraction. Special attention is recommended for women with OASI and levator injury as they would be at high risk of future pelvic floor disorders. The benefits of implementation of an intensive, focused and structured pelvic floor rehabilitation program needs to be evaluated in these women. This article is protected by copyright. All rights reserved