Lesioni del muscolo elevatore dell'ano nel post-partum: studio ecografico transperineale

Abstract

The female pelvic floor is a complex anatomical and functional system, whose structure is the result of evolutionary adaptations linked to the compromise between bipedalism, encephalization, and obstetric needs. Within this structure, the levator ani muscle (LAM) plays a fundamental role in supporting the pelvic viscera, controlling urinary and fecal continence, and supporting sexual function. Vaginal delivery is the most traumatic event for the pelvic floor during a woman's entire life, subjecting the LAM to levels of stretching that, during the second stage of labor and especially during the crowning phase of the fetal head, can far exceed the thresholds considered physiologically tolerable for striated muscle. Biomechanical models based on magnetic resonance imaging have shown that the medial pubococcygeal bundle can reach a stretch ratio of more than three times its resting length, exceeding the estimated ‘non-injurious’ threshold for skeletal muscles by more than 200%. In this context, pelvic floor trauma should not be considered a rare or exceptional event, but rather a possible consequence of vaginal delivery, the severity of which is influenced by a combination of obstetric factors, maternal characteristics, and duration of exposure to mechanical stress. LAM trauma is traditionally divided into macrotrauma and microtrauma. Macrotrauma is generally described as a partial or total avulsion of the LAM from its pubic insertion site, while microtrauma is characterized by irreversible overstretching of the hiatus area, known as “ballooning.” These two conditions are not mutually exclusive, as they can coexist and represent different expressions of the same injury process, with partially different determinants and functional implications. The clinical diagnosis of LAM trauma in the postpartum period presents numerous difficulties. Physical examination and simple inspection of the birth canal show low sensitivity in identifying LAM lesions, which often remain clinically occult. In this scenario, 3D/4D transperineal ultrasound has established itself as the diagnostic method of choice, thanks to its non-invasive nature, the possibility of performing dynamic assessments (at rest, during contraction, and during the Valsalva maneuver), and the high reproducibility of the measured parameters. The use of Tomographic Ultrasound Imaging (TUI) allows for a systematic, multi-layered analysis of LAM integrity, reducing the risk of underestimating partial avulsions, while measuring the hiatus area at maximum Valsalva allows for objective documentation of the presence of microtrauma. The main objective of the study was to determine the prevalence of postpartum LAM trauma in a population of primiparous women, using 3D/4D transperineal ultrasound and distinguishing between macrotrauma and microtrauma. Secondary objectives included analyzing the association between LAM trauma and pelvic symptoms (urinary, anorectal, and sexual) and identifying the main obstetric and maternal risk factors associated with different types of injury. A prospective longitudinal observational study was conducted at the University Hospital of Pisa, involving primiparous women aged ≥ 18 years who had undergone vaginal delivery and were evaluated between 3 and 10 months after delivery. All participants underwent a urogynecological evaluation, 3D/4D transperineal ultrasound examination, and completed validated questionnaires (ICIQ-FLUTS, FSFI, and Wexner score). Macrotrauma was defined as partial or total avulsion of the LAM detected by TUI, while microtrauma was defined as hiatal ballooning with a genital hiatus area > 25 cm² at the peak of the Valsalva maneuver. Of the 213 women contacted, 68 completed the entire study protocol. The average age at delivery was approximately 34 years, and the assessment was performed on average 7.5 months after delivery. Macrotrauma of the LAM was found in 17.6% of women, exclusively in the form of partial avulsions, predominantly unilateral. Microtrauma emerged as the most common condition, being present in 38.2% of the study population. All women with macrotrauma also had microtrauma, supporting the hypothesis of a continuum of LAM damage. Overall, approximately 62% of participants had no ultrasound signs attributable to LAM trauma. Univariate analysis revealed a significant association between both types of trauma and operative delivery, the use of the Kristeller maneuver, episiotomy, and the duration of the expulsive stage. Neonatal parameters (weight and head circumference) were mainly correlated with microtrauma, while maternal age showed a significant correlation with macrotrauma. In addition, third- and fourth-degree perineal lacerations (OASIS) were significantly associated with LAM trauma, particularly macrotrauma. From a clinical point of view, both microtrauma and macrotrauma were associated with a higher prevalence of urinary and anorectal disorders. In particular, women with LAM trauma had higher ICIQ-FLUTS and Wexner scores than women without injuries. Conversely, sexual function impairment, as assessed by the FSFI, was significantly higher only in women with macrotrauma, suggesting a gradient of functional impairment proportional to the severity of structural damage. Multivariate analysis, performed using separate logistic regression models for macrotrauma and microtrauma, identified independent predictive factors for each condition. For macrotrauma, the duration of the expulsive stage and maternal age at delivery were found to be independent determinants, while the mode of delivery did not maintain an independent association after adjustment. For microtrauma, however, the duration of the expulsion period and the mode of delivery were confirmed as independent predictors, with spontaneous delivery associated with a significantly lower risk than operative delivery. Overall, these results suggest that macrotrauma represents the expression of more severe structural damage, strongly influenced by the reduced tissue adaptability associated with maternal age, while microtrauma appears to be mainly related to the intensity and duration of mechanical stress exerted on the pelvic floor during the second stage of labor. Overall, the results confirm that postpartum levator ani muscle trauma is a frequent occurrence, often not clinically evident, with microtrauma being the most common manifestation, still poorly studied and likely underestimated in the literature. Transperineal 3D/4D ultrasound is confirmed as a fundamental method for the objective identification of different forms of LAM trauma and for the stratification of functional risk in the postpartum period. The integration of this approach into postpartum follow-up could allow for earlier identification of women at higher risk of pelvic dysfunction, facilitating the adoption of preventive interventions and more targeted clinical management strategies in the medium and long term