The Role of Transperineal Ultrasound for the Assessment of the Anorectal Angle and Its Relationship with Levator Ani Muscle Avulsion

Abstract

The relationship between the anorectal angle (ARA) and the levator ani muscle (LAM) is well known. In this study, we aimed to demonstrate that the ARA changes when LAM avulsion occurs after vaginal delivery. This was a secondary, observational retrospective study with data obtained from three previous studies. Using transperineal ultrasound, the presence of avulsion was assessed when abnormal insertion of the LAM was observed in three central slices. In addition, the ARA was assessed in the midsagittal plane (at rest, in Valsalva and at maximum contraction) as the angle between the posterior border of the distal part of the rectum and the central axis of the anal canal. The ARA was higher in patients with bilateral LAM avulsion than in patients without LAM avulsion at rest (131.8 ± 14.1 vs. 136.2 ± 13.8), in Valsalva (129.4 ± 15.5 vs. 136.5 ± 14.4) and at maximum contraction (125.7 ± 15.5 vs. 132.3 ± 13.2). The differences between both groups expressed as the odds ratio (OR) adjusted for maternal age were 1.031 (95% confidence interval (CI), 1.001–1.061; p = 0.041) at rest, 1.036 (95% CI, 1.008–1.064; p = 0.012) in Valsalva and 1.031 (95% CI, 1.003–1.059; p = 0.027) at maximum contraction. In conclusion, LAM avulsion produces an increase in the ARA at rest, during contraction and in Valsalva, especially in cases of bilateral LAM avulsion.

Reproducibility of the anorectal angle with transperineal ultrasound

“…A retrospective observational study was performed with data acquired from patients that had been included in a previous study (18). Forty patients were randomly selected from the previously described study (18), including 20 patients with LAM avulsion and 20 patients without LAM avulsion.…”

“…A retrospective observational study was performed with data acquired from patients that had been included in a previous study (18). Forty patients were randomly selected from the previously described study (18), including 20 patients with LAM avulsion and 20 patients without LAM avulsion. All patients were primiparous, had delivered vaginally at term, had given written informed consent to participate in the study and did not have pelvic floor corrective surgery.…”

“…The ARA is modified in patients with continence issues and, in addition, it has also been observed that age, body mass index and parity can affect the ARA (17). In fact, patients with levator ani muscle (LAM) avulsion have a wider ARA than patients without LAM avulsion (18).…”

“…However, this interobserver variation has been lessened in a subsequent publication (8). Different ultrasound methodologies have also been used for ARA assessment and have been validated as alternatives for the ARA measurement, such as threedimensional (3D) endovaginal ultrasound (20) and 3D transperineal ultrasound (18). The difference between them lies in the fact that 3D transperineal ultrasound (18) does not require the introduction of ultrasound transducers inside the anal canal, as occurs with 3D endovaginal probe (20).…”

“…Different ultrasound methodologies have also been used for ARA assessment and have been validated as alternatives for the ARA measurement, such as threedimensional (3D) endovaginal ultrasound (20) and 3D transperineal ultrasound (18). The difference between them lies in the fact that 3D transperineal ultrasound (18) does not require the introduction of ultrasound transducers inside the anal canal, as occurs with 3D endovaginal probe (20). Therefore, it is reasonable to think that the use of transperineal ultrasound can provide more reproducible ARA measurements, something that has not been established by 3D endovaginal probe (20) or defecography (8,19).…”