Asymmetric Sphincter Innervation is Associated With Fecal Incontinence After Anal Sphincter Trauma During Childbirth

Aims: Functional asymmetry of pelvic floor innervation has been shown to exist in healthy subjects, and has been proposed to be a predictor of increased risk for fecal incontinence in case of trauma. However, this remains to be shown for different clinical conditions such as traumatic childbirth.

Methods: A conventional surface EMG system was used to assess the innervation of the external anal sphincter. A symmetry index was used to define the relative EMG amplitude asymmetry of the external anal sphincter between 0 (symmetric) and 1 (asymmetric). Three cohorts were studied: 40 nulliparous women in the third trimester (Study 1), 15 primiparous women within 6 months following vaginal delivery without clinically apparent anal sphincter trauma (Study 2), and 50 women after childbirth-related third or fourth degree perineal tear 6-12 months postpartum (Study 3). Furthermore, all women underwent conventional anorectal manometry.

Results: Sixteen or forty nulliparous women reported signs of fecal incontinence; however, relative asymmetry was not correlated to symptom severity (P = 0.345), and not to manometric measures (Study 1). In Study 2, Women who had suffered clinically apparent anal sphincter trauma (P = 0.07) tended to have a stronger association between incontinence and asymmetry. In Study 3, 19/50 women reported moderate to severe incontinence. Asymmetry and symptom severity were significantly correlated (P < 0.001). Patients with incontinence had a significantly higher asymmetry score than their continent counterparts.

Conclusion: Functional asymmetry of anal sphincter innervation is significantly associated with incontinence symptoms, but only after childbirth-related sphincter injuries and therefore, should be regarded as an additional risk factor.