What type of terminology should be applied to define levator ani muscle avulsion?

Depósito de investigación de la Universidad de Sevilla https://idus.us.es/ Esta es la versión aceptada del artículo publicado en: This is a accepted manuscript of a paper published in: Ultrasound in Obstetrics & Gynecology (2025) DOI: 10.1002/uog.29232 Copyright: © 1999-2025 John Wiley & Sons, Inc or related companies. All rights reserved, includig rights for text and data mining and training or artificial inteligence technologies or similar technologies. El acceso a la versión publicada del artículo puede requerir la suscripción de la revista. Access to the published version may require subscription. “This is the peer reviewed version of the following article: García-Mejido JA, Sainz-Bueno JA. What type of terminology should be applied to define levator ani muscle avulsion? Ultrasound Obstet Gynecol. 2025 Apr 18. doi: 10.1002/uog.29232, which has been published in final form at 10.1002/uog.29232. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. This article may not be enhanced, enriched or otherwise transformed into a derivative work, without express permission from Wiley or by statutory rights under applicable legislation. Copyright notices must not be removed, obscured or modified. The article must be linked to Wiley’s version of record on Wiley Online Library and any embedding, framing or otherwise making available the article or pages thereof by third parties from platforms, services and websites other than Wiley Online Library must be prohibited." What type of terminology should be applied to define levator ani muscle avulsion? J. A. García-Mejido1* and J. A. Sainz-Bueno1 1Department of Surgery, Faculty of Medicine, University of Seville, Seville, Spain *Correspondence. (e-mail: [email protected]) The avulsion of the levator ani muscle (LAM) occurs during vaginal delivery1 and is associated closely with future pelvic floor dysfunction, such as pelvic organ prolapse. Due to the clinical relevance of LAM avulsion in the development of pelvic floor disorders, there has been an increase in the number of publications examining its progression over time. However, recent publications based on ultrasound studies have defined LAM avulsion using different terminologies, relying on either anatomical or purely ultrasound-based criteria2–4, without establishing which definition is the most appropriate. Therefore, our objective was to justify how LAM avulsion diagnosed in an ultrasound study should be defined. However, to study LAM avulsion properly, the anatomical peculiarities of the LAM need to be understood. In 2015, Kim et al. described in cadavers that the LAM originates tangentially from the periosteum covering the pubic bone and the nature of this attachment changes from the medial to lateral regions and can be divided into three regions: medial, central, and lateral.. The medial muscular region has a direct insertion into the bone, the central muscular region attaches to the periosteum through a thin aponeurotic membrane and the lateral muscular region connects to the arcus tendineus levator ani, where it fuses with the iliococcygeus muscle2. Based on these findings, Kim et al. classified LAM injuries into two types according to their anatomical appearance: Type I, in which the injury is limited to the more central individual portions of the LAM while preserving the levator arch intact; and Type II, which is associated with the complete detachment of the LAM, in which the levator arch is detached entirely from the pubic bone, resulting in a loss of the normal architecture of the pelvic sidewall2. On the other hand, we have ultrasound criteria that define LAM avulsion. These criteria were established in 2011 and define ‘complete avulsion’ as the discontinuity between the inferior pubic ramus and the LAM in all three central slices of the tomographic representation3, and ‘partial avulsion’ as an abnormal insertion of the LAM in at least one tomographic ultrasound image slice but in less than three central slices4. The conceptual difference between the anatomical and ultrasound definitions of LAM avulsion lies in the different study methodologies applied. The anatomical criterion bases its definition on the rupture of the muscle from the most central to the most lateral region, while the ultrasound criterion is based on standardized visualization of the injury in axial slices using ultrasound. At this point, one may ask: which definition is the most accurate? To answer this question, we must understand how the LAM becomes injured. It has been established that the medial portions of the LAM undergo a greater degree of stretching during the second stage of labor5. Therefore, it would be logical to assume that these more central muscular portions of the LAM are at the highest risk of suffering stretch-related injuries. As a result, the anatomical concept may be more accurate than the ultrasound concept for defining LAM avulsion. However, if we attempt to correlate both concepts, we may mistakenly think that Type-I avulsion corresponds to partial avulsion and Type II corresponds to complete avulsion. Nevertheless, when applying this association, we face the issue of how to define Type-I avulsions that are present in all three central slices of the tomographic representation (Figure 1). We have observed that this type of trauma can be described using ultrasound6 and that it may undergo a ‘healing’ process over time, as the levator arch remains intact7. Similarly, a recent publication concluded that LAM avulsions that show some degree of improvement over time are partial rather than complete8. However, on inspection of figure 2 in the article, we noted that a bilateral complete avulsion observed in a patient at 3 months postpartum (figure 2a) evolved into a clear partial avulsion at 2.1 years on the left side (figure 2b). By carefully examining the image at 3 months postpartum (figure 2a), we observed that the left avulsion is complete, as it is present in all three central slices of the tomographic representation, and it is also a Type-I avulsion because the levator arch remains intact8. For all these reasons, we conclude that the anatomical concept (Type I or Type II) and the ultrasound concept (partial or complete) of LAM avulsion are not mutually exclusive but rather complementary, we propose that both should be included when describing LAM avulsion. References: 1. García-Mejido JA, Fernández-Palacín A, Suarez-Serrano CM, MedranoSanchez E, Sainz JA. Successive intraand postpartum measurements of levator-urethra gap to establish timing of levator avulsión. Ultrasound Obstet Gynecol. 2019;54(6):840-842. 2. Kim J, Betschart C, Ramanah R, Ashton-Miller JA, DeLancey JO. Anatomy of the pubovisceral muscle origin: macroscopic and microscopic findings within the injury zone. Neurourol Urodyn. 2015;34(8):774-780. 3. Dietz H, Bernardo M, Kirby A, Shek K. Minimal criteria for the diagnosis of avulsion of the puborectalis muscle by tomographic ultrasound. Int Urogynecol J. 2011;22(6):699-704. 4. Dietz HP, Shek KL, Low GK. All or nothing? A second look at partial levator avulsion. Ultrasound Obstet Gynecol. 2022;60(5):693-7. 5. Lien KC, Mooney B, DeLancey JO, Ashton-Miller JA. Levator ani muscle stretch induced by simulated vaginal birth. Obstet Gynecol. 2004; 103: 31–40. 6. García-Mejido JA, Sainz JA. Type of levator ani muscle avulsion as predictor for the disappearance of avulsión. Neurourol Urodyn. 2020;39(8):2293-2300. 7.Garcia-Mejido J, Gonzalez-Diaz E, Ortega I, Martin-Martinez A, FernandezPalacin A, Sainz-Bueno J. Multicenter study of the evolution of different types of avulsion over the 12 months after delivery. Int J Gynaecol Obstet. 2023; 160:9397. 8. Dietz HP, Shek KL, Descallar J. Do some levator avulsions improve over time?. Ultrasound Obstet Gynecol. 2024;64(6):818-823. Figure legend Figure 1 Multislices pelvic floor imaging showing Type-I levator ani muscle avulsion (*) with levator arch intact (white arrow), which can also be classified as complete avulsion since it is present in all three central sections of tomographic representation.