Levator Morphology and Strength After Obstetric Avulsion of the Levator Ani Muscle

Two minutes is sufficient to characterize the viscoelastic properties of the human lower birth canal during the first stage of labor

BACKGROUND

The lower birth canal is the final constriction through which a fetal head must pass for delivery. Unfortunately, injuries to the lower birth canal tissues occur in up to 19 % of first-time vaginal deliveries due to the 300 % stretch required.

METHODS

This is a secondary analysis of data from 56 healthy nullipara recorded by a lower birth canal dilator during the first stage of labor. A four parameter Fractional Zener rheological Model was used to characterize the canal viscoelastic properties during the first stage of labor. We tested the (null) hypothesis that the Model constants identified during the initial 20 s ramp-and-5-min-hold dilation from 40 to 55 mm will not accurately predict the final hoop tension after 60 min of slower dilation.

FINDINGS

The null hypothesis was rejected in that when the four Model parameters were calculated for all nullipara from the 20-s-ramp-and-5-min-hold data, the relative fit error was 8 ± 4 %, and the relative prediction error after 60 min of dilation was 10 ± 5 %. Furthermore, when the Model constants were instead calculated from the 20 s ramp and only the initial 90 s of the 5-min-hold, the error was still acceptable: 13 ± 4 % for relative fit and 13 ± 18 % for relative prediction.

INTERPRETATION

Two minutes is sufficient to characterize canal viscoelastic properties during the first stage of labor and identify those with stiffer tissues at higher risk for a pelvic floor injury during delivery. This could form the basis for a clinical test predicting injury.

Pelvic floor imaging in women with hemorrhoidal disease: An anatomical feasibility study

OBJECTIVE

To compare pelvic floor muscle and organ structures in women with and without hemorrhoidal disease (HD) using magnetic resonance imaging (MRI).

MATERIAL AND METHODS

Pelvic MRI measurements and computer-based medical records of women diagnosed with HD between January 2018 and March 2021 were analyzed. Parameters including pubococcygeal distance, puborectal distance, posterior anorectal angle, obturator internus muscle area, presence of levator ani muscle defect, genital hiatus length, vaginal length, uterocervical angle, cervix-upper vagina angle, and cervix-middle vagina angle were evaluated. The control group consisted of women without HD, matched for age and body mass index.

RESULTS

Puborectal hiatus distance was higher in the HD group (59.2 ​± ​8.7 ​mm vs. 55.5 ​± ​7.1 ​mm, p ​= ​0.03). Similarly, the distance to the M line was greater in the HD group (18.3 ​± ​4.8 ​mm vs. 16 ​± ​4.6 ​mm, p ​= ​0.04). Obturator internus muscle area was found to be lower in the HD group compared to the non-HD group (1721 ​± ​291.4 ​mm2 vs. 1897.5 ​± ​352.5 ​mm2, p ​= ​0.02). Additionally, the presence of unilateral levator ani muscle defect was higher in HD patients (p ​= ​0.03). There was a negative correlation between birthweight and obturator internus muscle area (r ​= ​-0.388, p ​= ​0.02), and a positive correlation with M line distance (r ​= ​0.344, p ​= ​0.04).

CONCLUSION

Levator ani muscle defects and obturator internus muscle area, indicators of pelvic floor dysfunction, are more common in patients with hemorrhoidal disease.

Levator ani muscle avulsion and subsequent vaginal delivery: 8-year longitudinal follow-up

OBJECTIVES

To assess the evolution of levator ani muscle (LAM) avulsion from 1 year to 8 years after first delivery in women with and those without subsequent vaginal delivery. In addition, to assess whether women with full or partial avulsion 8 years after first delivery have larger LAM hiatal area and more symptoms of pelvic organ prolapse compared to women with normal LAM insertion.

METHODS

In this single-center longitudinal study, 195 women who were primiparous at the start of the study were included and underwent transperineal ultrasound examination 1 year and 8 years after first delivery. Muscle insertion was assessed by tomographic ultrasound imaging in the axial plane. Full LAM avulsion was defined as abnormal muscle insertion in all three central slices. Partial LAM avulsion was defined as abnormal muscle insertion in one or two central slices. Eight years after the first delivery, LAM hiatal area was assessed at rest, during maximum pelvic floor muscle contraction and on maximum Valsalva maneuver. To assess symptoms of pelvic organ prolapse, the vaginal symptoms module of the International Consultation on Incontinence Questionnaire was used.

RESULTS

At 1-year follow-up, 25 (12.8%) women showed signs of LAM avulsion, of whom 20 fulfilled the sonographic criteria of full avulsion and five of partial avulsion. Eight years after the first delivery, 35 (17.9%) women were diagnosed with avulsion, of whom 25 were diagnosed with full avulsion and 10 with partial avulsion. No woman with partial or full avulsion at 1 year had improved avulsion status at 8-year follow-up. Of the 150 women who had subsequent vaginal delivery, 21 (14.0%) women were diagnosed with partial or full LAM avulsion 1 year after first delivery, and 31 (20.7%) women were diagnosed with partial or full avulsion 8 years after first delivery. Of the 45 women without subsequent vaginal delivery, one woman with partial avulsion 1 year after first delivery was diagnosed with full avulsion at 8-year follow-up. All women with full avulsion at 1-year follow-up were diagnosed with full avulsion at 8-year follow-up regardless of whether they had subsequent vaginal delivery. At 8-year follow-up, women with full avulsion had statistically significantly larger LAM hiatal area compared to women with normal muscle insertion. Mean ± SD vaginal symptom scores ranged between 5.5 ± 5.7 and 6.0 ± 4.0 and vaginal symptom quality of life scores ranged between 0.9 ± 1.4 and 1.5 ± 2.2 and did not differ significantly between women with normal muscle insertion and women with partial or full avulsion at 8-year follow-up.

CONCLUSIONS

More LAM avulsions were present 8 years compared with 1 year after first delivery in women with subsequent vaginal delivery. Except for one primipara, all women without subsequent vaginal delivery had unchanged LAM avulsion status between 1 year and 8 years after their first delivery. Larger LAM hiatal area was found in women with full avulsion compared to those with normal muscle insertion at 8-year follow-up. Vaginal symptoms scores were low and did not differ between women with normal muscle insertion and those with partial or full avulsion at 8-year follow-up. © 2024 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Contributory effects of individual characteristics on pelvic floor distress in women with pelvic floor dysfunctions

OBJECTIVE

To determine individual characteristics (i.e. sociodemographic and medical, obstetric and gynecological, and musculoskeletal and anthropometric parameters) for greater pelvic floor distress (PFD).

METHODS

A cross-sectional study was performed in 253 women with pelvic floor dysfunction. PFD was assessed using the Pelvic Floor Distress Inventory-20 (PFDI-20). The score of Urogenital Distress Inventory-6 (UDI-6) was used to perform secondary analyses. Sociodemographic, medical, and obstetric & gynecological parameters were recorded. Waist and hip circumferences and pelvic diameters were measured as anthropometric parameters. Pearson test, t-test, and linear regression analyses were conducted with a significance level of 0.05.

RESULTS

Education level (r = -0.23, p < .001; r = -0.24, p < .001), number of vaginal births (r = 0.15, p = .012; r = 0.12, p = .048), total vaginal birth weight (r = 0.15, p = .021; r = 0.16, p = .019), and Body Mass Index (r = 0.12, p = .043; r = 0.16, p = .007) were significantly correlated with the higher PFDI-20 and UDI-6 scores. The maternal age at the first vaginal birth (r = -0.13, p = .049) and pelvic antero-posterior diameter (r = 0.17, p = .013) were also significantly correlated with higher UDI-6 score. Linear regression analyses revealed that younger age (Beta coefficient (β) = -1.10, p = .005), greater symptom duration (β = 2.28, p = .001), the presence of chronic cough/constipation (β = 25.72, p = .001), and increased total vaginal birth weight (β = 2.38, p = .030) were associated with the greater PFDI-20 score. Increased pelvic antero-posterior diameter (β = 0.88, p = .049) was a contributory factor for the greater UDI-6 score.

CONCLUSION

This study showed that younger age, chronic cough/constipation, higher total vaginal birth weight, greater symptom duration, and pelvic antero-posterior diameter can be contributors of greater PFD. We suggest further longitudinal studies that better reveal the causal relationship between individual characteristics and PFD.

Multiparity Reduces Urethral and Vaginal Pressures Following the Bulboglandularis Muscle Stimulation in Rabbits

Unlike male mammals showing a well-delimited external urethral sphincter, female mammals have urogenital sphincters shaped by muscles like the urethrovaginal sphincter. Childbirth-related injuries affect morphometry and function of urogenital sphincters in women, which frequently underlies pelvic floor disorders, including stress urinary incontinence and pelvic organ prolapse. The bulboglandularis muscle (Bgm) seems to shape a urogenital sphincter in rabbits. We determined herein the effect of multiparity on urethral and vaginal pressures generated by the Bgm stimulation in age-matched nulliparous and multiparous chinchilla-breed rabbits to stimulate the Bgm with trains of ascending frequencies (from 1 to 100 Hz; 4 s duration each). Subsequently, the Bgm was excised, measured in width, and weighed. Significant differences (P ≤ 0.05) were determined with Mann-Whitney U or Student t-tests or repeated measures two-way ANOVA followed by Tukey tests. Spearman's partial coefficients were calculated to investigate the correlation between the highest pressure (urethral or vaginal) and the Bgm width. Multiparity reduced the weight and the width in the Bgm origin and medial regions. Urethral and vaginal pressures increased in response to the electrical stimulation of Bgm with frequencies from 20 to 100 Hz. Multiparas showed significant reductions in both types of pressures. We detected a strong correlation (conditioned by multiparity) between the medial Bgm width and the highest vaginal pressure. Our present findings demonstrate that multiparity impairs the function of Bgm, resulting in diminished urethral and vaginal pressures. Furthermore, the significant narrowness of the Bgm was correlated with the vaginal pressure recorded.

A comparison of MRI-based pelvic floor support measures between young and old women with prolapse

INTRODUCTION AND HYPOTHESIS

We sought to 1) test the hypothesis that young women (≤45 years) with pelvic organ prolapse have a higher prevalence of major levator ani muscle (LAM) defects than old women (≥70 years) with prolapse and 2) compare level II/III measurements between young and old women with prolapse and age-matched controls to evaluate age-related mechanistic differences in the disease process.

METHODS

A secondary analysis examined four groups of parous women: young prolapse (YPOP, n = 17); old prolapse (OPOP, n = 17); young controls (YC, n = 15); old controls, (OC, n = 13). Prolapse was defined as any compartment at or beyond the hymen with vaginal bulge symptoms. Genital hiatus (GH) was measured on clinical exam. Major LAM defects and level II/III measurements (UGH: urogenital hiatus, LA: levator area, and apex location) were assessed on MRI at rest and strain, and the difference (Δ) between measurements calculated. Principal component analysis was used to evaluate levator plate (LP) shape.

RESULTS

Major LAM defects occurred in 42% of YPOP and 47% of OPOP (p > .99). GHrest was 1.5 cm larger in OPOP versus YPOP (p < .001) and 2 cm larger in OPOP versus OC (p < .001). Regardless of prolapse status, LArest and UGHrest on MRI increased with age. YPOP had larger ΔLA (p = .04), ΔUGH (p = .03), and Δapex than OPOP (p = .01). Resting LP shape was more dorsally oriented in OPOP versus YPOP (p = .02) and OC versus YC (p = .004).

CONCLUSIONS

Prolapse in young women cannot be solely explained by a higher LAM defect prevalence. GH size and other measures of level II/III pelvic support worsen with age regardless of prolapse status.

Opportunities to Advance Postpartum Pelvic Floor Care With a Health Equity-based Conceptual Framework

An essential part of postpartum care includes the evaluation and treatment of pelvic floor disorders (PFDs). Postpartum PFDs are common and occur in over 40% of postpartum women. Despite significant advancements in urogynecology to understand postpartum PFDs and their treatments, there has been a lack of attention to addressing equity in postpartum pelvic floor care. In this article, we address the current scientific understanding of postpartum PFDs while adapting a health equity-based conceptual framework to highlight areas of opportunity in optimizing postpartum pelvic floor care.

Hiatal failure: effects of pregnancy, delivery, and pelvic floor disorders on level III factors

INTRODUCTION AND HYPOTHESIS

The failure of the levator hiatus (LH) and urogenital hiatus (UGH) to remain closed is not only associated with pelvic floor disorders, but also contributes to recurrence after surgical repair. Pregnancy and vaginal birth are key events affecting this closure. An understanding of normal and failed hiatal closure is necessary to understand, manage, and prevent pelvic floor disorders.

METHODS

This narrative review was conducted by applying the keywords "levator hiatus" OR "genital hiatus" OR "urogenital hiatus" in PubMed. Articles that reported hiatal size related to pelvic floor disorders and pregnancy were chosen. Weighted averages for hiatal size were calculated for each clinical situation.

RESULTS

Women with prolapse have a 22% and 30% larger LH area measured by ultrasound at rest and during Valsalva than parous women with normal support. Women with persistently enlarged UGH have 2-3 times higher postoperative failure rates after surgery for prolapse. During pregnancy, the LH area at Valsalva increases by 29% from the first to the third trimester in preparation for childbirth. The enlarged postpartum hiatus recovers over time, but does not return to nulliparous size after vaginal birth. Levator muscle injury during vaginal birth, especially forceps-assisted, is associated with increases in hiatal size; however, it only explains a portion of hiatus variation-the rest can be explained by pelvic muscle function and possibly injury to other level III structures.

CONCLUSIONS

Failed hiatal closure is strongly related to pelvic floor disorders. Vaginal birth and levator injury are primary factors affecting this important mechanism.

Three-Dimensional Pelvic Floor Ultrasound Assessment of Pelvic Organ Prolapse: Minimal Levator Hiatus and Levator Ani Deficiency Score

Purpose

The purpose of this study was to determine whether levator ani deficiency (LAD) scores and minimal levator hiatus (MLH) areas affect Pelvic Organ Prolapse Quantification (POP-Q) stage.

Methods

This study was a retrospective chart review of patients with pelvic organ prolapse (POP) at Seoul Songdo Hospital between August 2019 and August 2020. Three-dimensional (3D) pelvic floor ultrasound, preoperative anal manometry, and other physiological tests were performed in 78 patients with POP symptoms. We divided the patients into mild prolapse and severe prolapse groups based on the POP-Q. We examined the LAD and MLH areas. LAD scores were categorized as mild, moderate, or severe.

Results

There were 32 patients (41.0%) in the mild prolapse group (POP-Q stage I and II) and 46 (59.0%) in the severe prolapse group (POP-Q stage III and IV). The mean LAD score was significantly higher in severe prolapse group (13.33±2.49 vs. 8.19±2.92, P<0.001), and the rate of severe deficiency was also significantly higher in the severe prolapse group (29 [63.0%] vs. 2 [6.3%], P<0.001). The mean MLH was also significantly larger in the severe prolapse group (17.91±2.74 cm² vs. 14.95±2.60 cm², P<0.001). In addition, both MLH and LAD scores tended to increase at each stage.

Conclusion

There is a strong positive correlation between the POP-Q stage and the MLH and LAD scores that can be seen on 3D pelvic floor ultrasound. The findings of this study, by objectively demonstrating LAD and MLH in women with POP, are an important contribution to POP.

Surface electromyography of the pelvic floor at 6-8 weeks following delivery: a comparison of different modes of delivery

INTRODUCTION AND HYPOTHESIS

The objective of this study was to compare the impact of different modes of delivery, especially forceps delivery (FD), on pelvic floor muscles (PFMs) through vaginal surface electromyography (sEMG) in primiparous women at early (6-8 weeks) postpartum.

METHODS

A total of 1259 primiparous women with full-term singleton births were included in this cross-sectional study. Of these, 98 were delivered by forceps, 865 underwent spontaneous vaginal delivery (SD) and 296 underwent elective cesarean delivery (CD). Clinical demographic characteristics and vaginal sEMG variables of parturients 6-8 weeks after birth were collected and analyzed using SPSS software. One-way ANOVA with Bonferroni correction, Chi-square test or Student's t-test was used according to the variable type. Spearman correlation and binary logistic regression analyses were also used. P/α ≤ 0.05 was considered statistically significant.

RESULTS

Amplitude of fast and sustained contractions on sEMG in the FD group was significantly lower compared with the CD and SD groups. The sEMG amplitude of all contractions was significantly higher in the CD group compared with the FD and SD groups (P < 0.01). According to binary logistic regression analysis, mode of delivery was a major influencing factor in sEMG.

CONCLUSIONS

An early postpartum sEMG test appears to be helpful for the assessment of PFM activity. Mode of delivery was a major influencing factor on sEMG. Forceps delivery significantly inversely influenced PFM activity.

Mechanisms of hiatus failure in prolapse: a multifaceted evaluation

INTRODUCTION AND HYPOTHESIS

We investigated whether factors influencing pelvic floor hiatal closure are inter-related or independent, hypothesizing that (1) hiatus size is moderately correlated with levator defect, pelvic floor muscle strength, and change in hiatus size with contraction and (2) urogenital hiatus (UGH) and levator hiatus (LH) measures are similar in patients with anterior wall (AW) and posterior wall (PW) prolapse.

METHODS

This cross-sectional case-control study included subjects with AW prolapse (n = 50), PW prolapse (n = 50), and normal support (n = 50). Hiatus measurements and levator defects were assessed on MRI, and vaginal closure force was measured with an instrumented speculum. Pearson correlation coefficients and simple and multivariable linear regression models were performed.

RESULTS

During contraction, LH narrowed 47% more in the PW compared to AW group (p = 0.001). With straining, LH lengthened 34% more in the PW than AW group (p < 0.001). With straining, UGH and LH lengthening was greater by 72% and 44% in those with major compared to no/minor defect (p < 0.001 and p = 0.004). Contraction strength explained, at most, 4% of UGH (r = 0.17) or LH (r = 0.20) shortening during contraction (r = 0.17 and r = 0.20, respectively), indicating that these factors are largely independent. After controlling for prolapse size, resting UGH and levator defect status were associated with straining UGH (p < 0.001, p = 0.004), but muscle strength and resting tone were not.

CONCLUSIONS

Hiatus measures are complex and differ according to prolapse occurrence and type. They are, at best, only weakly correlated with pelvic floor muscle strength and movement during contraction.

The usual suspect: cross-sectional study of fundal pressure at second stage of delivery and the association with pelvic floor damage

INTRODUCTION AND HYPOTHESIS

Uterine fundal pressure is applied to accelerate birth by increasing the expulsive force of the uterus in the second stage of delivery. The aim of the study was to evaluate the effect of using uterine fundal pressure during the second stage of delivery on the rate of pelvic floor damage among primiparous women using three-dimensional transperineal ultrasonography.

METHODS

The women were divided into two groups: the fundal pressure group included women where the fundal pressure maneuver was applied (n = 39); the control group included women who delivered spontaneously without fundal pressure (n = 47). 3D-TPU was performed within 48 h of delivery, and LAM biometry, LAM defect and loss of tenting were determined.

RESULTS

Anteroposterior hiatal dimensions on resting, maximal Valsalva and maximal PFMC were found to be higher in the fundal pressure group (p < 0.0001, p = 0.008, p = 0.007, respectively). The mean hiatal area at rest was larger in the fundal pressure group than in the control group (p = 0.04). The rate of LAM defect was significantly higher in the fundal pressure group (p = 0.001). The rate of loss of tenting was significantly higher in the fundal pressure group (p < 0.0001). According to multivariate regression models, the fundal pressure was the only independent factor associated with LAM defect (OR = 5.63; 95% CI = 12.01-15.74) and loss of tenting (OR = 8.74; 95% CI = 2.89-26.43).

CONCLUSIONS

Fundal pressure during the second stage of delivery is associated with a higher risk of LAM defect and loss of anterior vaginal wall support.

CLINICAL TRIAL REGISTRATION

NCT03752879.

Pelvic organ prolapse as a function of levator ani avulsion, hiatus size, and strength

BACKGROUND

Obstetrical levator ani muscle avulsion is detected after 10%-30% of vaginal deliveries and is associated with pelvic organ prolapse later in life. However, the mechanism by which levator avulsion may contribute to prolapse is unknown.

OBJECTIVES

This study investigated the extent by which size of the levator hiatus and pelvic muscle weakness may explain the association between levator avulsion and pelvic organ prolapse.

STUDY DESIGN

This was a supplementary study of a longitudinal cohort of parous women enrolled 5-10 years after first delivery and assessed annually for prolapse (defined as descent beyond the hymen) for up to 9 annual visits. For this substudy, vaginally parous participants were assessed for levator avulsion using 3-dimensional transperineal ultrasound. Ultrasound was performed at a median interval of 11 years from delivery. Ultrasound volumes also were used to measure levator hiatus area with Valsalva. Pelvic muscle strength was measured with perineometry. Women with and without pelvic organ prolapse were compared for levator avulsion, levator hiatus area, and pelvic muscle strength, using multivariable logistic regression yielding a measure of mediation. Bootstrap methods were used to calculate the confidence interval corresponding to the measure of mediation by hiatus area and pelvic muscle strength.

RESULTS

Prolapse was identified in 109 of 429 (25%) and was significantly associated with levator avulsion (odds ratio, 4.17; 95% confidence interval, 2.28-7.31). Prolapse also was associated with levator hiatus area (odds ratio, 1.52 per 5 cm²; 95% confidence interval, 1.34-1.73) and inversely with muscle strength (odds ratio, 0.87 per 5 cm H₂O; 95% confidence interval, 0.81-0.94). In a multivariable logistic model including levator avulsion, levator hiatus area, and strength, the association between levator avulsion and prolapse was substantially attenuated and indeed was no longer statistically significant (odds ratio, 1.75; 95% confidence interval, 0.91-3.39). Hiatus area and strength mediated 61% (95% confidence interval, 34%-106%) of the association between avulsion and prolapse. Furthermore, since the 95% confidence interval for this estimate contained 100%, it cannot be ruled out that the 2 markers fully mediate the effect of avulsion on prolapse.

CONCLUSIONS

The strong association between pelvic organ prolapse and levator avulsion can be explained to a large extent by a larger levator hiatus and weaker pelvic muscles after levator avulsion.

Persistent occiput posterior position and stress distribution in levator ani muscle during vaginal delivery computed by a finite element model

INTRODUCTION AND HYPOTHESIS

Objective of this study was to develop an MRI-based finite element model and simulate a childbirth considering the fetal head position in a persistent occiput posterior position.

METHODS

The model involves the pelvis, fetal head and soft tissues including the levator ani and obturator muscles simulated by the hyperelastic nonlinear Ogden material model. The uniaxial test was measured using pig samples of the levator to determine the material constants. Vaginal deliveries considering two positions of the fetal head were simulated: persistent occiput posterior position and uncomplicated occiput anterior position. The von Mises stress distribution was analyzed.

RESULTS

The material constants of the hyperelastic Ogden model were measured for the samples of pig levator ani. The mean values of Ogden parameters were calculated as: μ1 = 8.2 ± 8.9 GPa; μ2 = 21.6 ± 17.3 GPa; α1 = 0.1803 ± 0.1299; α2 = 15.112 ± 3.1704. The results show the significant increase of the von Mises stress in the levator muscle for the case of a persistent occiput posterior position. For the optimal head position, the maximum stress was found in the anteromedial levator portion at station +8 (mean: 44.53 MPa). For the persistent occiput posterior position, the maximum was detected in the distal posteromedial levator portion at station +6 (mean: 120.28 MPa).

CONCLUSIONS

The fetal head position during vaginal delivery significantly affects the stress distribution in the levator muscle. Considering the persistent occiput posterior position, the stress increases evenly 3.6 times compared with the optimal head position.