Hypothesis / aims of study
Levator ani avulsion has been described as the loss of continuity between the levator ani muscle and the pelvic sidewall, which can be diagnosed by a tomographic sonography following an internationally standardized method. (1)
Levator ani avulsion plays a key role in the pathophysiology of pelvic organ prolapse (POP). The use of an obstetric forceps has been identified as an independent intrapartum risk factor for levator ani injury and there’s a higher risk of bilateral lesions with forceps compared with spontaneous and vacuum assisted births. In some studies, the incidence rate of avulsion on the right-hand side was higher than the left for all modes of birth, however, most of these studies don’t show statistical differences. It is plausible that this could be secondary to the difference of fetal head rotation if in a right occipitoposterior position. It is unlikely though that this difference could be attributed to the laterality of an episiotomy, as a mediolateral episiotomy was suggested not to be associated with the occurrence of levator avulsion. (2,3)
The aim of this study was to analyze the presence and type of levator ani trauma using tomographic sonography in patients with genital organ prolapse and defining determining factors of such trauma in our population.
Study design, materials and methods
This is a descriptive restrospective study that includes all patients diagnosed with uterine prolapse with or without anterior wall prolapse, who underwent a 3D/4D transperineal ultrasound in our hospital between November of 2018 and December of 2023. Data was collected from the patient’s clinical records concerning obstetric history, history of pathology, data from a complete pelvic floor clinical exam and data from the ultrasound itself.
The ultrasound was conducted by a single operator using a Voluson E Expert system and performed following Dietz described technique.
Patients were classified in two groups depending on their sonographic diagnosis: patients with absence of levator ani avulsion (integrity of levator ani muscle) and patients with levator ani avulsion including bilateral levator avulsion and unilateral levator avulsion.
Statistical analysis was performed with PASW statistics 18.0. Qualitative variables are expressed as absolute values and percentages. For the study of categorical variables, chi-square test and Fisher’s was used as appropiate. Univariate analysis with odds ratio was performed for those factors that presented statistically significant differences between both groups. For all tests, a p<0,05 was considered statistically significant.
Results
We managed to include 173 patients. In table 1, we registered the characteristics of our sample including epidemiological data, obstetric history and clinical assessment. Regarding the transperineal sonography, integrity of levator any muscle was found in 78 (45,1%) patients, bilateral levator ani avulsion was registered in 64 (37%) patients and unliateral levator ani avulsion was observed in 31 (17,9%), of the latter 29 (16,8%) where right levator ani avulsions and 2 (1,1%) were left levator ani avulsion.
Comparing both groups, we observed that there was a statistically significant higher rate of menopausal patients in the integrity group. Instrumented assisted birth and specifically forceps assisted birth also presented a statistically significant higher rate in the avulsion group. Surprisingly, we observed that there was also a significant higher rate of anal incontinence in the integrity group. The rest of factors assessed didn’t show significant differences between groups (Table 2).
Odds ratio analysis (Table 2) showed that in our sample menopausal women were less likely to be diagnosed with levator ani avulsion. As expected, record of instrumental assisted birth and forceps assisted birth was a risk factor for developing levator ani avulsion. Anal incontinence didn’t show less likelihood of levator ani avulsion.
Interpretation of results
As expected, record of obstetric forceps or instrumental birth was a risk factor of levator ani injury in our sample. It came as a surprise that menopausal state was more prevalent in the muscle integrity group, though this makes sense, given that there is a relative bias of selection when finding our sample in women that consulted with organ prolapse; in women that didn’t have an avulsion of levator ani, mechanism of POP could be related to age or menopausal state. There was also a higher rate of anal incontinence in the integrity group. Being sphincter anal injuries the firstcause for anal incontinence, this finding could be explained by the fact that an obstetric anal sphincter injury in these women could have decreased tension in the levator ani during birth, thus becoming a protective factor for levator avulsion; this though wasn’t demonstrated when odds ratio was applied.
It is also important to emphasize the difference between the rates of unilateral llevator avulsion laterality. Right-hand side avulsion was much more prevalent than left-hand side, as noted before, this has also been observed in other series. Further studies would shed light on the mechanism of these findings, though given our bias of selection, a higher rate of occiput-posterior births than the general population in our sample could be the cause of these difference, though this wasn’t analyzed.