Alteration of anal sphincter function in patients with levator avulsion: observational study

The prevalence of levator avulsion after vaginal delivery ranges from 10 to 30 %. To our knowledge, no previous studies have used anorectal manometry (AM) to assess this injury's impact on the functionality of the anal sphincter complex. We hypothesized that women with levator avulsion have lower manometric pressures.

A prospective observational study was conducted on 83 women, 61 in the birth group and 22 in the control group. Patients in the deliveries group were recruited in the period immediately postpartum. The control group was recruited through hospital announcements. All patients underwent 3D transperineal (3D TPUS) and 2D endoanal ultrasound (2D EAUS), as well as AM at 6 months postpartum. Median maximum resting and squeeze pressures were measured, and the presence or absence of levator ani muscle (LAM) avulsion and/or occult sphincter injury was evaluated.

Hiatal area at rest was significantly higher in women with vaginal birth compared with controls (p = 0.02) and there was a trend toward statistical significance compared with the cesarean section group (p = 0058). No statistical differences were observed for the hiatal area regarding Valsalva, external anal sphincter thickness, and internal anal sphincter thickness among groups. There was a significantly higher prevalence of levator avulsion in the vaginal birth group (32.43 %) compared with the controls (0 %) and the cesarean section group (5.8 %; p < 0001). There were 5 occult sphincter injuries detected at ultrasound, all of them in the vaginal birth group. Lower squeeze pressure was observed in patients with levator injury compared with control group patients and patients without avulsion (112.2 mmHg vs 128.2 mmHg and 121.2mmH; p = 0.032). Finally, there was no difference in resting pressure (p = 0.541) or squeeze pressure (p = 0.449) between patients with and those without occult anal sphincter injuries.

Levator avulsion is associated with lower manometric squeeze pressure (p = 0.032).