Levator Ani Muscle Avulsion During Vaginal Delivery

Childbirth is one of the most important experiences in most womenS lives. Compared to cesarean delivery, vaginal delivery is typically considered a more natural method of childbirth. However, vaginal delivery can lead to severe maternal birth trauma, mainly manifested as anal sphincter tear and anal levator ani muscle avulsion [1,2]. Compared to women who have not given birth or have only delivered via cesarean section, vaginal delivery constitutes a significant risk factor for pelvic floor dysfunction, and the trauma it causes to the mother may exceed conventional understanding [3,4].

The levator ani muscle (LAM) is an critically important structure connecting the pubis on both sides, surrounding the anus, rectum and vagina. It plays a crucial role in supporting and maintaining the function of the pelvic organs. During vaginal delivery,the LAM is the most vulnerable area [5]. Studies have shown that 10-35 % of women undergoing vaginal delivery experience partial or complete LAM avulsion, that is, the puborectalis is detached from the pubis [[6], [7], [8]].

In the past, the diagnosis of LAM avulsion mainly relied on digital palpation performed by urologists, which was heavily dependent on the clinician’s experience, and the diagnostic outcomes were highly subjective. In recent years, four-dimensional (4D) transperineal ultrasound (TPUS) with tomographic ultrasound imaging (TUI) has gradually standardized the diagnosis of LAM avulsion [9]. Complete avulsion of the LAM, clinically manifested as palpable detachment of the puborectalis of the subpubic LAM, was defined in TUI as discontinuity between muscle and bone in the three central images [10]. 4D TPUS has the characteristics of high repeatability and non-invasive, and is comparable to expensive magnetic resonance imaging (MRI) in terms of diagnostic consistency, which can reach 90 % [[11], [12], [13], [14]]. Tho,it should be noted that the diagnosis of LAM avulsion using 4D TPUS also depends on the operator’s extensive experience,and the operator requires standardized learning and practical training to obtain images of high diagnostic quality [15,16].

At present, a number of studies have proved that two-dimensional (2D) transperineal ultrasound is in good agreement with 4D ultrasound in the diagnosis of LAM avulsion [[17], [18], [19], [20]]. For instance, in a 2022 published cohort study by Martina et al., which used a prospective observational design, the diagnostic concordance between 2D and 4D transperineal ultrasound was