Levator ani thickness variations in symptomatic and asymptomatic women using magnetic resonance-based 3-dimensional color mapping

Finite element analysis of female pelvic organ prolapse mechanism: current landscape and future opportunities

The prevalence of pelvic organ prolapse (POP) has been steadily increasing over the years, rendering it a pressing global health concern that significantly impacts women's physical and mental wellbeing as well as their overall quality of life. With the advancement of three-dimensional reconstruction and computer simulation techniques for pelvic floor structures, research on POP has progressively shifted toward a biomechanical focus. Finite element (FE) analysis is an established tool to analyze the biomechanics of complex systems. With the advancement of computer technology, an increasing number of researchers are now employing FE analysis to investigate the pathogenesis of POP in women. There is a considerable number of research on the female pelvic FE analysis and to date there has been less review of this technique. In this review article, we summarized the current research status of FE analysis in various types of POP diseases and provided a detailed explanation of the issues and future development in pelvic floor disorders. Currently, the application of FE analysis in POP is still in its exploratory stage and has inherent limitations. Through continuous development and optimization of various technologies, this technique can be employed with greater accuracy to depict the true functional state of the pelvic floor, thereby enhancing the supplementation of the POP mechanism from the perspective of computer biomechanics.

International urogynecology consultation chapter 3 committee 2; conservative treatment of patient with pelvic organ prolapse: Pelvic floor muscle training

INTRODUCTION AND HYPOTHESIS

This manuscript from Chapter 3 of the International Urogynecology Consultation (IUC) on Pelvic Organ Prolapse (POP) describes the current evidence and suggests future directions for research on the effect of pelvic floor muscle training (PFMT) in prevention and treatment of POP.

METHODS

An international group of four physical therapists, four urogynecologists and one midwife/basic science researcher performed a search of the literature using pre-specified search terms on randomized controlled trials (RCTs) in Ovid Medline, EMBASE, CINAHL, Cochrane, PEDro and Scopus databases for publications between 1996 and 2021. Full publications or expanded abstracts in English or in other languages with abstracts in English were included. The PEDro rating scale (0-10) was used to evaluate study quality. Included RCTs were reviewed to summarize the evidence in six key sections: (1) evidence for PFMT in prevention of POP in the general female population; (2) evidence for early intervention of PFMT in the peripartum period for prevention and treatment of POP; (3) evidence for PFMT in treatment of POP in the general female population; (4) evidence for perioperative PFMT; (5) evidence for PFMT on associated conditions in women with POP; (6) evidence for the long-term effect of PFMT on POP. Full publications in English or in other languages with abstracts in English and expanded abstracts presented at international condition specific societies were included. Internal validity was examined by the PEDro rating scale (0-10).

RESULTS

After exclusion of duplicates and irrelevant trials, we classified and included 2 preventive trials, 4 trials in the post-partum period, 11 treatment trials of PFMT for POP in the general female population in comparison with no treatment or lifestyle interventions, 10 on PFMT as an adjunct treatment to POP surgery and 9 long-term treatment trials. Only three treatment studies compared PFMT with the use of a pessary. The RCTs scored between 4 and 8 on the PEDro scale. No primary prevention studies were found, and there is sparse and inconsistent evidence for early intervention in the postpartum period. There is good evidence/recommendations from 11 RCTs that PFMT is effective in reducing POP symptoms and/or improving POP stage (by one stage) in women with POP-Q stage I, II and III in the general female population, but no evidence from 9/10 RCTs that adding PFMT pre- and post -surgery for POP is effective. There are few long-term follow-up studies, and results are inconsistent. There are no serious adverse effects or complications reported related to PFMT.

CONCLUSIONS

There are few studies on prevention and in the postpartum period, and the effect is inconclusive. There is high-level evidence from 11 RCTs to recommend PFMT as first-line treatment for POP in the general female population. PFMT pre- and post-POP surgery does not seem to have any additional effect on POP. PFMT is effective and safe but needs thorough instruction and supervision to be effective.

Embodiment of intra-abdominal pressure in a flexible multibody model of the trunk and the spinal unloading effects during static lifting tasks

The role of intra-abdominal pressure (IAP) in spinal load reduction has remained controversial, partly because previous musculoskeletal models did not introduce the pressure generating mechanism. In this study, an integrated computational methodology is proposed to combine the IAP change with core muscle activations. An ideal gas relationship was introduced to calculate pressure distribution within the abdominal cavity. Additionally, based on flexible multibody dynamics, a muscle membrane element was developed by incorporating the muscular fiber deformation, inter-fiber stiffness, and volume constancy. This element was then utilized in discretizing the diaphragm and transversus abdominis, forming an IAP-muscle coupling system of the abdominal cavity. Based on this methodology, a forward dynamic simulation of spinal flexion was presented to examine the unloading effect of abdominal breathing. The results confirm that core muscle contraction during the abdominal breathing cycle can substantially reduce the forces of spinal compression together with trunk extensor muscles, and this effect is more pronounced when the IAP increase is produced by contraction of the transversus abdominis. This unloading effect still holds even with the co-activation of other abdominal muscles, providing a potential choice when designing trunk movements during weight-lifting tasks.

Biomechanical trade-offs in the pelvic floor constrain the evolution of the human birth canal

Compared with most other primates, humans are characterized by a tight fit between the maternal birth canal and the fetal head, leading to a relatively high risk of neonatal and maternal mortality and morbidities. Obstetric selection is thought to favor a spacious birth canal, whereas the source for opposing selection is frequently assumed to relate to bipedal locomotion. Another, yet underinvestigated, hypothesis is that a more expansive birth canal suspends the soft tissue of the pelvic floor across a larger area, which is disadvantageous for continence and support of the weight of the inner organs and fetus. To test this "pelvic floor hypothesis," we generated a finite element model of the human female pelvic floor and varied its radial size and thickness while keeping all else constant. This allowed us to study the effect of pelvic geometry on pelvic floor deflection (i.e., the amount of bending from the original position) and tissue stresses and stretches. Deflection grew disproportionately fast with increasing radial size, and stresses and stretches also increased. By contrast, an increase in thickness increased pelvic floor stiffness (i.e., the resistance to deformation), which reduced deflection but was unable to fully compensate for the effect of increasing radial size. Moreover, larger thicknesses increase the intra-abdominal pressure necessary for childbirth. Our results support the pelvic floor hypothesis and evince functional trade-offs affecting not only the size of the birth canal but also the thickness and stiffness of the pelvic floor.

The pathophysiology of stress urinary incontinence: a systematic review and meta-analysis

Introduction and hypothesis

To evaluate the evidence for pathologies underlying stress urinary incontinence (SUI) in women.

Methods

For the data sources, a structured search of the peer-reviewed literature (English language; 1960–April 2020) was conducted using predefined key terms in PubMed and Embase. Google Scholar was also searched. Peer-reviewed manuscripts that reported on anatomical, physiological or functional differences between females with signs and/or symptoms consistent with SUI and a concurrently recruited control group of continent females without any substantive urogynecological symptoms. Of 4629 publications screened, 84 met the inclusion criteria and were retained, among which 24 were included in meta-analyses.

Results

Selection bias was moderate to high; < 25% of studies controlled for major confounding variables for SUI (e.g., age, BMI and parity). There was a lack of standardization of methods among studies, and several measurement issues were identified. Results were synthesized qualitatively, and, where possible, random-effects meta-analyses were conducted. Deficits in urethral and bladder neck structure and support, neuromuscular and mechanical function of the striated urethral sphincter (SUS) and levator ani muscles all appear to be associated with SUI. Meta-analyses showed that observed bladder neck dilation and lower functional urethral length, bladder neck support and maximum urethral closure pressures are strong characteristic signs of SUI.

Conclusion

The pathology of SUI is multifactorial, with strong evidence pointing to bladder neck and urethral incompetence. While there is also evidence of impaired urethral support and levator ani function, standardized approaches to measurement are needed to generate higher levels of evidence.

Is pelvic floor muscle strength and thickness associated with pelvic organ prolapse in Nepali women? - A cross-sectional study

BACKGROUND

Pelvic floor muscle function has been shown to be inversely associated with pelvic organ prolapse in Western women, however differences have been documented between ethnic groups.

OBJECTIVE

To determine if pelvic floor muscle strength and thickness and hiatal area are associated with pelvic organ prolapse in Nepali women.

METHODS

This cross-sectional study included non-pregnant Nepali women ≥18 years attending an outpatient gynecology clinic in Kathmandu, Nepal. A clinical examination included the pelvic organ prolapse quantification (POP-Q)- system examination and Modified Oxford Scale. Puborectalis muscle thickness and hiatal area were assessed using 3D/4D translabial ultrasound. Statistical analysis included Pearson's correlation and multiple regression (p<0.05).

RESULTS

Of the 123 women; 14 (11%) had POP-Q stage 0 prolapse, 29 (24%) stage I, 69 (56%) stage II, 8 (7%) stage III, and 3 (2%) stage IV. Mean±SD Modified Oxford Scale was 3.37±0.48 and muscle thickness was 1.14±0.21cm, hiatal area at rest was 14.67±3.11cm² and on contraction was 11.29±2.51cm². No associations were found between pelvic floor muscle strength or thickness and POP-Q stages 0-IV. There was a positive correlation found between hiatal area at rest and pelvic organ prolapse stage (r=0.34, p<0.001)and hiatal area on contraction and prolapse stage (r=0.30, p<0.001) and a negative correlation between pelvic floor muscle strength and hiatal area on contraction (r=-0.36, p<0.001).

CONCLUSION

In contrast to previous findings, pelvic floor muscle strength and thickness are not associated with pelvic organ prolapse in this sample of Nepali women. It is important to consider these findings when developing pelvic organ prolapse treatment and management strategies in this population.

Pelvic magnetic resonance imaging parameters predict urinary incontinence after robot-assisted radical prostatectomy

OBJECTIVE

Urinary incontinence (UI) is a major prostate cancer (PCa) treatment-related morbidity. It has been reported that post-prostatectomy UI is related to the width of the pelvic floor muscles (PFM) and the length of the urethra. However, the details of these anatomical parameters are unknown. The aim of this study was to investigate whether preoperative pelvic parameters or anatomical parameters of the urethra, as measured by magnetic resonance imaging (MRI), are correlated with UI.

METHODS

Between 2010 and 2017, 571 patients with localized PCa underwent robot-assisted radical prostatectomy (RARP) at Okayama University Hospital. Patients treated by a single experienced surgeon were included in the study. Preoperative prostate volume, obturator internal muscle, anal sphincter muscle, levator ani muscle (LAM), urethra wall thickness (UWT), and membranous urethral length (MUL) were measured by MRI. Patients were divided into two groups depending on leakage status 1 year after RARP using Expanded Prostate Index Composite Item 1.

RESULTS

Seventy patients were included in this retrospective study. Based on leakage status, 37 and 33 patients were allocated to the no-leakage and leakage groups, respectively. There were significant differences between the two groups in age (P = 0.03), MUL (P < 0.001), UWT (P = 0.03), and LAM (P = 0.001). Multivariate logistic regression analyses revealed that MUL and LAM predicted UI 1 year after RARP.

CONCLUSIONS

Pelvic parameters measured by MRI before RARP may be useful in the prediction of UI. In particular, MUL and LAM can predict postoperative UI by strict definition.

Technique development and measurement of cross-sectional area of the pubovisceral muscle on MRI scans of living women

INTRODUCTION AND HYPOTHESIS

Measurements of the anatomic cross-sectional area (CSA) of the pubovisceral muscle (PVM) in women are confounded by the difficulty of separating the muscle from the adjacent puborectal (PRM) and iliococcygeal (ICM) muscles when visualized in a plane orthogonal to the fiber direction. We tested the hypothesis that it might be possible to measure the PVM CSA within a defined region of interest based on magnetic resonance images (MRI).

METHODS

MRI scans of 11 women with unilateral PVM tears and seven primiparous women with intact muscles following elective C-section were used to identify the PVM injury zone defined by the mean location of its boundaries with the adjacent intact PRM and ICM from existing anatomic reference points using 3D Slicer and ImageJ software. Then, from the 15 or more 2-mm transverse slices available, the slice with the maximum anatomic CSA of the left and right PVM was found in 24 primiparous women with bilaterally intact muscles who had delivered via C-section.

RESULTS

Mean [± standard deviation (SD)] of the maximum left or right PVM cross-section areas for the 24 women, measured by two different raters, was 1.25 ± 0.29 cm² (range 0.75-1.86). The 5th, 50th, and 95th percentile values were 0.77, 1.23, and 1.80 cm², respectively. Inter- and intrarater measurement repeatability intraclass correlation coefficients exceeded 0.89 and 0.90, respectively.

CONCLUSIONS

It is possible to use MRI to identify the volume of interest with the maximum anatomic cross section of the PVM belly while minimizing the inadvertent inclusion of adjacent PRM or ICM in that measurement.

Recommended standardized terminology of the anterior female pelvis based on a structured medical literature review

BACKGROUND

The use of imprecise and inaccurate terms leads to confusion amongst anatomists and medical professionals.

OBJECTIVE

We sought to create recommended standardized terminology to describe anatomic structures of the anterior female pelvis based on a structured review of published literature and selected text books.

STUDY DESIGN

We searched MEDLINE from its inception until May 2, 2016, using 11 medical subject heading terms to identify studies reporting on anterior female pelvic anatomy; any study type published in English was accepted. Nine textbooks were also included. We screened 12,264 abstracts, identifying 200 eligible studies along with 13 textbook chapters from which we extracted all pertinent anatomic terms.

RESULTS

In all, 67 unique structures in the anterior female pelvis were identified. A total of 59 of these have been previously recognized with accepted terms in Terminologia Anatomica, the international standard on anatomical terminology. We also identified and propose the adoption of 4 anatomic regional terms (lateral vaginal wall, pelvic sidewall, pelvic bones, and anterior compartment), and 2 structural terms not included in Terminologia Anatomica (vaginal sulcus and levator hiatus). In addition, we identified 2 controversial terms (pubourethral ligament and Grafenberg spot) that require additional research and consensus from the greater medical and scientific community prior to adoption or rejection of these terms.

CONCLUSION

We propose standardized terminology that should be used when discussing anatomic structures in the anterior female pelvis to help improve communication among researchers, clinicians, and surgeons.

MRI changes of pelvic floor and pubic bone observed in primiparous women after childbirth by normal vaginal delivery

Objective

To identify and characterize changes in the pelvic floor and pubic bone, using magnetic resonance imaging, in primiparous women with normal vaginal delivery, in comparison with nulliparous women.

Methods

Pelvic MR images from ten primiparous women, 6–7 weeks after normal vaginal delivery, and ten nulliparous women were obtained from January to April 2014. The selected women were scanned using a multiplanar T2FRFSE sequence and T2fsFRFSE sequence. Changes in the pelvic floor and pubic bone in primiparous women, including tears of the levator ani fibers, pubic bone edema, and fractures, were assessed on the MR images in comparison with images from normal nulliparous women. Injury to the levator ani was evaluated and scored. The incidence, location and the extent of injury to the levator ani and pubic bone were characterized further.

Results

Eight out of ten primiparous women had imaging abnormalities after normal vaginal delivery. Three women had unilateral tears of the pubococcygeus, in which the defect in the muscle was located at or near its origin at the pubic bone, and one had a pubococcygeus tear accompanied by bilateral spilling of the vagina. Four women had partial tears of the iliococcygeus: one was a bilateral tear, and three were unilateral. None had a tear of the coccygeus. Eight women had pubic bone marrow edema; one was accompanied by a pubic bone fracture line. None of the nulliparous women had any abnormality of the pelvic floor and pubic bone.

Conclusion

Abnormalities of the pelvic floor and pubic bone were observed in primiparous women but not in nulliparous women. In primiparous women, most levator ani muscle tears are at or near the point of origin, and pubococcygeus injuries are usually accompanied by pubic bone marrow edema.

Biomechanical properties of synthetic surgical meshes for pelvic prolapse repair

Synthetic meshes are widely used for surgical repair of different kind of prolapses. In the light of the experience of abdominal wall repair, similar prostheses are currently used in the pelvic region, to restore physiological anatomy after organ prolapse into the vaginal wall, that represent a recurrent dysfunction. For this purpose, synthetic meshes are surgically positioned in contact with the anterior and/or posterior vaginal wall, to inferiorly support prolapsed organs. Nonetheless, while mesh implantation restores physiological anatomy, it is often associated with different complications in the vaginal region. These potentially dangerous effects induce the surgical community to reconsider the safety and efficacy of mesh transvaginal placement. For this purpose, the evaluation of state-of-the-art research may provide the basis for a comprehensive analysis of mesh compatibility and functionality. The aim of this work is to review synthetic surgical meshes for pelvic organs prolapse repair, taking into account the mechanics of mesh material and structure, and to relate them with pelvic and vaginal tissue biomechanics. Synthetic meshes are currently available in different chemical composition, fiber and textile conformations. Material and structural properties are key factors in determining mesh biochemical and mechanical compatibility in vivo. The most significant results on vaginal tissue and surgical meshes mechanical characterization are here reported and discussed. Moreover, computational models of the pelvic region, which could support the surgeon in the evaluation of mesh performances in physiological conditions, are recalled.

Characteristics associated with pelvic organ prolapse in women with significant levator ani muscle deficiency

INTRODUCTION AND HYPOTHESIS

Age is a factor associated with symptomatic pelvic organ prolapse (POP) among women with significant levator ani deficiency.

METHODS

This cross-sectional study included patients who were referred for varied pelvic floor disorders, had 3D endovaginal ultrasound as part of their evaluation, and were diagnosed with significant levator ani muscle deficiency defined as a score of 12 or more on 3D endovaginal ultrasound. Patients were categorized as having no pelvic organ prolapse (stages 0 and 1), or symptomatic prolapse (stages 2-4).

RESULTS

Seventy-six women were available for analysis and found to have significant levator ani muscle deficiency, including 51 with symptomatic POP and 25 without POP. Patients with symptomatic POP were older, (mean age 66 (SD ± 11.8) vs 48 (SD ± 17.3) years; p <0.0001), had greater mean minimal levator hiatus (MLH) area (19.7 cm(2) (SD ± 4.6) vs 17.5 cm(2) (SD ± 3.5); p = 0.048), and were more likely to be menopausal (91.3 % vs 54.5 %; p <0.001) compared with those with no POP. In a modified Poisson regression analysis excluding nulliparous women, increasing age (RR = 2.39, 95 % CI 1.03-5.55) and smoking (RR = 1.34, 95 % CI 1.08-1.67) remained associated with symptomatic POP after controlling for one another and the MLH area.

CONCLUSIONS

Among women with significant levator ani deficiency, older women and smokers had an increased prevalence of symptomatic POP. On average, women without POP, but with significant levator ani deficiency were 18 years younger than women with POP and significant muscle deficiency.

How well can levator ani muscle morphology on 3D pelvic floor ultrasound predict the levator ani muscle function?

INTRODUCTION AND HYPOTHESIS

The aim of our study was to assess the performance of levator ani muscle deficiency (LAD) evaluated by 3D endovaginal ultrasound (EVUS) to detect pelvic floor muscle function as assessed by digital examination.

METHODS

This cross-sectional study was conducted among 77 patients referred to our urogynecology clinic for pelvic floor dysfunction symptoms. Patients underwent physical examinations including digital pelvic muscle strength assessment using the Modified Oxford scale (MOS). EVUS volumes were evaluated and levator ani muscles were scored according to a validated LAD scoring system. MOS scores were categorized as nonfunctional (scores 0-1) and functional (scores 2-5).

RESULTS

Mean age of participants was 56 (SD ± 12.5) and 71% were menopausal. Overall, 32.5% had nonfunctional muscle strength and 44.2% were classified as having significant LAD. LAD identified by ultrasound had a sensitivity of 60% (95% CI 41 -79%) for detecting nonfunctional muscle and a specificity of 63% (95% CI 50 -77%) for detecting functional muscle. Overall, LAD demonstrated fair ability to discriminate between patients with and those without poor muscle function (area under the ROC curve = 0.70 [95% CI 0.58-0.83]). Among patients with an LAD score of 16-18, representing almost total muscle avulsion, 70% had nonfunctional MOS scores, whereas in patients with normal/minimal LAD (scores of 0-4), 89.5% had functional MOS scores.

CONCLUSIONS

Levator ani deficiency and MOS scales were moderately negatively correlated. Among patients with normal morphology or the most severe muscle deficiency, LAD scores can identify the majority of patients with functional or nonfunctional MOS scores respectively.

Anal sphincter complex: 2D and 3D endoanal and translabial ultrasound measurement variation in normal postpartum measurements

INTRODUCTION AND HYPOTHESIS

Women may experience anal sphincter anatomy changes after vaginal birth (VB) or Cesarean delivery (CD). Therefore, accurate and acceptable imaging options to evaluate the anal sphincter complex (ASC) are needed. ASC measurements may differ between translabial (TLUS) and endoanal (EAUS) ultrasound imaging and between 2D and 3D US. The objective of this analysis was to describe measurement variation between these modalities.

METHODS

Primiparous women underwent 2D and 3D TLUS imaging of the ASC 6 months after VB or CD. A subset of women also underwent EAUS measurements. Measurements included internal anal sphincter (IAS) thickness at proximal, mid, and distal levels and the external anal sphincter (EAS) at 3, 6, 9, and 12 o'clock positions, as well as bilateral thickness of the pubovisceralis muscle (PVM).

RESULTS

There were 433 women presenting for US: 423 had TLUS and 64 had both TLUS and EAUS of the ASC. All IAS measurements were significantly thicker on TLUS than EAUS (all p < 0.01), while EAS measurements were significantly thicker on EAUS (p < 0.01). PVM measurements with 3D or 2D imaging were similar (p > 0.20). On both TLUS and EAUS, there were multiple sites where significant asymmetry existed in left versus right measurements.

CONCLUSIONS

US modality used to image the ASC introduces small but significant changes in measurements, and the direction of the bias depends on the muscle and location being imaged.

Magnetic resonance imaging of the pelvic floor: from clinical to biomechanical imaging

This article reviews the current role of magnetic resonance imaging in the study of the pelvic floor anatomy and pelvic floor dysfunction. The application of static and dynamic magnetic resonance imaging in the clinical context and for biomechanical simulation modeling is assessed, and the main findings are summarized. Additionally, magnetic resonance-based diffusion tensor imaging is presented as a potential tool to evaluate muscle fiber morphology. In this article, focus is set on pelvic floor muscle damage related to urinary incontinence and pelvic organ prolapse, sometimes as a consequence of vaginal delivery. Modeling applications that evaluate anatomical and physiological properties of pelvic floor are presented to further illustrate their particular characteristics. Finally, finite element method is described as a method for modeling and analyzing pelvic floor structures' biomechanical performance, based on material and behavioral properties of the tissues, and considering pressure loads that mimic real-life conditions such as active contraction or Valsalva maneuver.

Are pelvic floor muscle thickness and size of levator hiatus associated with pelvic floor muscle strength, endurance and vaginal resting pressure in women with pelvic organ prolapse stages I-III? A cross sectional 3D ultrasound study

AIMS

To investigate if pelvic floor muscle (PFM) thickness and area of levator hiatus (LH) are associated with manometry measured PFM function in 109 women with pelvic organ prolapse (POP) stages I-III.

METHODS

In this cross-sectional study pubovisceral muscle thickness and LH area were assessed with three-dimensional transperineal ultrasound at rest and analyzed in the axial plane. PFM function was assessed with manometry and included strength, endurance, and vaginal resting pressure. Relationships were investigated using univariate linear logistic regressions models, Pearson product-moment correlation coefficient and hierarchical multiple regression.

RESULTS

The mean age was 49 (SD 12). There was a significant positive moderate association between muscle thickness and PFM strength (r = 0.49, P < 0.001) and endurance (r = .45, P < 0.001). A moderate negative association was found between LH area and vaginal resting pressure (r = -0.46, P < 0.001), strength (r = -0.41, P < 0.001) and endurance (r = -0.40, P < 0.001). Multivariate analyses included PFM strength, endurance, vaginal resting pressure, age, parity, BMI and socioeconomic status. Muscle thickness was best explained by PFM strength and LH area was best explained by vaginal resting pressure. However, PFM function explained only 20.0% and 26.4% of the variance in muscle thickness and LH area after controlling for age, parity, BMI, and socioeconomic status.

CONCLUSION

There are moderate associations between measurements using ultrasound and manometry in POP women. Thicker muscles and smaller LH were associated with higher strength and endurance. Smaller LH was additionally associated with higher vaginal resting pressure. Ultrasound and manometry measure different aspects of the PFM and cannot be used interchangeably.

A comparison of the effect of age on levator ani and obturator internus muscle cross-sectional areas and volumes in nulliparous women

AIMS

Functional tests have demonstrated minimal loss of vaginal closure force with age. So we tested the null hypotheses that age neither affects the maximum cross-sectional area (CSA) nor the volume of the levator muscle. Corresponding hypotheses were also tested in the adjacent obturator internus muscle, which served as a control for the effect of age on appendicular muscle in these women.

METHODS

Magnetic resonance images of 15 healthy younger (aged 21-25 years) and 12 healthy older nulliparous women (aged >63 years) were selected to avoid the confounding effect of childbirth. Models were created from tracing outlines of the levator ani muscle in the coronal plane, and obturator internus in the axial plane using 3D Slicer v. 3.4. Muscle volumes were calculated using Slicer, while CSA was measured using Imageware™ at nine locations. The hypotheses were tested using repeated measures analysis of variance with P < 0.05 being considered significant.

RESULTS

The effect of age did not reach statistical significance for the decrease in levator ani muscle maximum CSA or the decrease in volume (4.3%, P = 0.62 and 10.9%, 0.12, respectively). However, age did significantly adversely decrease obturator internus muscle maximum CSA and volume (24.5% and 28.2%, P < 0.001, respectively). Significant local age-related changes were observed dorsally in both muscles.

CONCLUSIONS

Unlike the adjacent appendicular muscle, obturator internus, the levator ani muscle in healthy nullipara does not show evidence of significant age-related atrophy.

Measuring the levator hiatus with axial MRI sequences: adjusting the angle of acquisition

AIMS

We aimed to compare MRI measurements of the female levator hiatus and the most caudal "levator ani" muscles between image slices in a plane axial to the body (AxB) and an axial plane parallel to the direction of the puborectalis muscle (AxPRM).

METHODS

We performed high-resolution, T2-weighted axial magnetic resonance imaging (in two different planes) on 20 sequentially recruited asymptomatic nulliparous women. Levator hiatus measurements were compared between the two planes.

RESULTS

The mean tilt angle of the AxPRM slices relative to the AxB slices was 18.9° (SD 8.5) and the area of the levator hiatus was 10% greater (P=0.04) in the AxPRM plane.

CONCLUSIONS

By rotating the acquisition plane to be parallel to the puborectalis muscle (sometimes called the plane of minimal hiatal dimensions), some of the measurements of the distal and medial pelvic floor muscles (and the hiatus defined by them) are altered. This issue is important because both MRI and 3D ultrasound are increasingly being used to evaluate the pelvic floor hiatus, and its relationship to childbirth injury and pelvic floor disorders. To make meaningful comparisons, it is important that both modalities are measuring the same thing.

Alterations in pelvic floor muscles and pelvic organ support by pregnancy and vaginal delivery in squirrel monkeys

INTRODUCTION AND HYPOTHESIS

The objective of this study was to measure the effects of pregnancy and parturition on pelvic floor muscles and pelvic organ support.

METHODS

Levator ani, obturator internus, and coccygeus (COC) muscle volumes and contrast uptake were assessed by MRI of seven females prior to pregnancy, 3 days, and 4 months postpartum. Bladder neck and cervix position were measured dynamically with abdominal squeezing.

RESULTS

The sides of three paired muscles were similar (p > 0.66). COC volumes were greater (p < 0.004) after parturition than before pregnancy or after recovery. COC contrast uptake increased (p < 0.02) immediately after delivery. Bladder neck position both in the relaxed state and abdominal pressure descended (p < 0.04) after delivery and descended further (p < 0.001) after recovery. Cervical position in the relaxed state before delivery was higher (p < 0.001) than postpartum but was unchanged (p = 0.50) with abdominal pressure relative to delivery.

CONCLUSION

In squirrel monkeys, coccygeus muscles demonstrate the greatest change related to parturition, and parturition-related bladder neck descent seems permanent.

Anatomy and histology of the lower urinary tract

The function of the lower urinary tract is basically storage of urine in the bladder and the at-will periodic evacuation of the stored urine. Urinary incontinence is one of the most common lower urinary tract disorders in adults, but especially in the elderly female. The urethra, its sphincters, and the pelvic floor are key structures in the achievement of continence, but their basic anatomy is little known and, to some extent, still incompletely understood. Because questions with respect to continence arise from human morbidity, but are often investigated in rodent animal models, we present findings in human and rodent anatomy and histology. Differences between males and females in the role that the pelvic floor plays in the maintenance of continence are described. Furthermore, we briefly describe the embryologic origin of ureters, bladder, and urethra, because the developmental origin of structures such as the vesicoureteral junction, the bladder trigone, and the penile urethra are often invoked to explain (clinical) observations. As the human pelvic floor has acquired features in evolution that are typical for a species with bipedal movement, we also compare the pelvic floor of humans with that of rodents to better understand the rodent (or any other quadruped, for that matter) as an experimental model species. The general conclusion is that the "Bauplan" is well conserved, even though its common features are sometimes difficult to discern.

In vivo assessment of anterior compartment compliance and its relation to prolapse

INTRODUCTION AND HYPOTHESIS

The objective of the study was to compare anterior compartment compliance between women with and without pelvic organ prolapse and to explore factors determining the extent of anterior compartment prolapse.

METHODS

Ten women with normal pelvic support and nine with anterior compartment prolapse were analyzed. Abdominal pressure was measured during Valsalva and simultaneous midsagittal dynamic MR imaging. The distance between the most dependent anterior vaginal wall point and a previously determined average nulliparous anterior vaginal wall point was measured. A best-fit line was determined when anterior vaginal wall displacement was plotted relative to abdominal pressure. The slope of this line is a measure of anterior compartment compliance. Multivariate analyses and t tests were performed.

RESULTS

Mean compliance (centimeters per centimeter of water) was higher for cases [0.05 +/- 0.006 standard error of the mean (SEM)] than controls (0.03 +/- .007, p = 0.039). Degree of anterior compartment prolapse correlated best with compliance (R (2) = 0.75, p < 0.01) and also with resting anterior vaginal wall point (R (2) = 0.55, p < 0.01).

CONCLUSIONS

Women with anterior compartment prolapse have a 67% more compliant support system compared with those with normal support. Both compliance and resting anterior vaginal wall location are predictors of the degree of anterior compartment prolapse.

Morphological changes after pelvic floor muscle training measured by 3-dimensional ultrasonography: a randomized controlled trial

OBJECTIVE

To investigate morphological and functional changes after pelvic floor muscle training in women with pelvic organ prolapse.

METHODS

This randomized controlled trial was conducted at a university hospital and a physical therapy clinic. One hundred nine women with pelvic organ prolapse stages I, II, and III were randomly allocated by a computer-generated random number system to pelvic floor muscle training (n=59) or control (n=50). Both groups received lifestyle advice and learned to contract the pelvic floor muscles before and during increases in intraabdominal pressure. In addition the pelvic floor muscle training group did individual strength training with a physical therapist and daily home exercise for 6 months. Primary outcome measures were pelvic floor muscle (pubovisceral muscle) thickness, levator hiatus area, pubovisceral muscle length at rest and Valsalva, and resting position of bladder and rectum, measured by three-dimensional ultrasonography.

RESULTS

Seventy-nine percent of women in the pelvic floor muscle training group adhered to at least 80% of the training protocol. Compared with women in the control group, women in the pelvic floor muscle training group increased muscle thickness (difference between groups: 1.9 mm, 95% confidence interval [CI] 1.1-2.7, P<.001), decreased hiatal area (1.8 cm, 95% CI 0.4-3.1, P=.026), shortened muscle length (6.1 mm, 95% CI 1.5-10.7, P=.007), and elevated the position of the bladder (4.3 mm, 95% CI 2.1-6.5, P<.000) and rectum (6.7 mm, 95% CI 2.2-11.8, P=.007). Additionally, they reduced the hiatal area and muscle length at maximum Valsalva indicating increased pelvic floor muscle stiffness.

CONCLUSION

Supervised pelvic floor muscle training can increase muscle volume, close the levator hiatus, shorten muscle length, and elevate the resting position of the bladder and rectum.

CLINICAL TRIAL REGISTRATION

www.clinicaltrials.gov, NCT00271297.

LEVEL OF EVIDENCE

I.

Selected interventions in nuclear medicine: gastrointestinal motor functions

The measurement of gastrointestinal functions by the use of scintigraphy is established in clinical practice and research. The most commonly used test is the gastric-emptying test, which is acknowledged as the gold standard to measure gastric motility and is conducted according to a consensus statement from the national nuclear medicine and motility societies. Other techniques are somewhat more esoteric (eg, measurement of gastric accommodation with single-photon emission computed tomography) or the scintigraphic approach is not the acknowledged gold standard (eg, colonic transit, rectoanal angle, and emptying, esophageal transit). The performance characteristics of many of the scintigraphic measurements have been published and the pros and cons established in the literature. Pharmacologic interventions may also be used during scintigraphy to aid in diagnosis and treatment. Gastrointestinal scintigraphy is an integral and important component of the assessment of gastrointestinal function.

Physical-based statistical shape modeling of the levator ani

The levator ani is the main muscular support of the pelvic floor organs and damage caused by childbirth can affect its function. The full functionality of this muscle group is still unknown but it is essential for effective surgical planning. To elucidate its functional significance, a physical-based statistical shape model was built from the levator ani surfaces of 15 subjects scanned in an open access scanner. Simulation of dynamic exercises was performed on the resulting surfaces with finite element analysis. Statistical shape modeling was performed on the training set consisting of the original and simulated shapes along with thickness and strain distributions. Simulation results are presented on 15 subjects. The statistical shape model shows good correspondence to inter- and intra-subject shape variability, with the modes of variation highlighting movement in the posterior of the levator ani as well as in the levator arms. Strain distribution plots and the modes of variation show results that correspond to clinical findings. Further validation of the technique and a repeatability test were performed on four subjects with internal global pressure readings taken from a perineometer and five patients suffering from minor pelvic floor disorders due to obstructed defaecation. A Mann-Whitney nonparametric test was used to compare the normal model fitting to the two subject groups.

A 3D finite element model of anterior vaginal wall support to evaluate mechanisms underlying cystocele formation

OBJECTIVES

To develop a 3D computer model of the anterior vaginal wall and its supports, validate that model, and then use it to determine the combinations of muscle and connective tissue impairments that result in cystocele formation, as observed on dynamic magnetic resonance imaging (MRI).

METHODS

A subject-specific 3D model of the anterior vaginal wall and its supports were developed based on MRI geometry from a healthy nulliparous woman. It included simplified representations of the anterior vaginal wall, levator muscle, cardinal and uterosacral ligaments, arcus tendineus fascia pelvis and levator ani, paravaginal attachments, and the posterior compartment. This model was then imported into ABAQUS and tissue properties were assigned from the literature. An iterative process was used to refine anatomical assumptions until convergence was obtained between model behavior under increases of abdominal pressure up to 168 cm H(2)O and deformations observed on dynamic MRI.

RESULTS

Cystocele size was sensitive to abdominal pressure and impairment of connective tissue and muscle. Larger cystocele formed in the presence of impairments in muscular and apical connective tissue support compared to either support element alone. Apical impairment resulted in a larger cystocele than paravaginal impairment. Levator ani muscle impairment caused a larger urogenital hiatus size, longer length of the distal vagina exposed to a pressure differential, larger apical descent, and resulted in a larger cystocele size.

CONCLUSIONS

Development of a cystocele requires a levator muscle impairment, an increase in abdominal pressure, and apical and paravaginal support defects.

Magnetic resonance assessment of pelvic anatomy and pelvic floor disorders after childbirth

To compare pelvic anatomy, using magnetic resonance imaging, between postpartum women with or without pelvic floor disorders. We measured postpartum bony and soft tissue pelvic dimensions in 246 primiparas, 6-12-months postpartum. Anatomy was compared between women with and without urinary or fecal incontinence, or pelvic organ prolapse; P < 0.01 was considered statistically significant. A deeper sacral hollow was significantly associated with fecal incontinence (P = 0.005). Urinary incontinence was marginally associated with a wider intertuberous diameter (P = 0.017) and pelvic arch (P = 0.017). There were no significant differences in pelvimetry measures between women with and without prolapse (e.g., vaginal or cervical descent to or beyond the hymen). We did not detect meaningful differences in soft tissue dimensions for women with and without these pelvic floor disorders. Dimensions of the bony pelvis do not differ substantially between primiparous women with and without postpartum urinary incontinence, fecal incontinence and prolapse.

Role of static and dynamic MR imaging in surgical pelvic floor dysfunction

Pelvic floor dysfunction (PFD) is a hidden women's health epidemic in the United States, with over 10% of women having a lifetime risk for undergoing a surgical repair for this problem. Given the paucity of understanding of PFD pathophysiology and the high rate of recurrence and repeat surgery, imaging plays a major role in its clinical management, especially for the preoperative assessment of patients with multicompartment defects and failed surgical repairs. The recent development of fast magnetic resonance (MR) imaging sequences allows noninvasive, radiation-free, rapid, high-resolution evaluation of the entire pelvis in one examination. The H line, M line, organ prolapse (HMO) classification system, which is applied to dynamic MR images, allows consistent standardization and grading of various forms of PFD. In addition, the HMO system clearly defines and differentiates between the two main components of PFD: pelvic floor relaxation and pelvic organ prolapse. In addition to serving as an objective diagnostic tool in patients with surgical PFD, MR imaging has tremendous potential to be used as a research tool in trying to understand the pathophysiology of these complex disorders.

Pelvic floor anatomy and applied physiology

Pelvic floor muscles have two major functions: they provide support or act as a floor for the abdominal viscera including the rectum; and they provide a constrictor or continence mechanism to the urethral, anal, and vaginal orifices (in females). This article discusses the relevance of pelvic floor to the anal opening and closure function, and discusses new findings with regards to the role of these muscles in the vaginal and urethra closure mechanisms.

Posterior compartment anatomy as seen in magnetic resonance imaging and 3-dimensional reconstruction from asymptomatic nulliparas

OBJECTIVE

The objective of the study was to identify characteristic anatomical features of the posterior compartment using magnetic resonance (MR) cross-sectional anatomy and 3-dimensional (3-D) modeling.

STUDY DESIGN

Supine, static proton-density MR images of 20 nulliparas were analyzed. MR images were used to create models in a selected exemplar.

RESULTS

The compartment's upper, mid, and lower segments are best seen in the axial plane. It is bounded inferiorly by the perineal body, ventrally by the posterior vaginal wall, and dorsally by the levator ani muscles and coccyx. In the upper portion, the compartment is bordered laterally by the uterosacral ligaments, whereas in the middle portion, there is more direct contact with the lateral levator ani muscles. In the lower portion, the contact becomes obliterated because the vagina and levator ani muscles become fused to each another and to the perineal body.

CONCLUSION

The posterior compartment has characteristic anatomic features in MR cross-sectional anatomy that can be further elucidated and integrated with 3-D anatomy.

Dynamic magnetic resonance imaging for grading pelvic organ prolapse according to the International Continence Society classification: which line should be used?

AIMS

To assess and compare the reliability of dynamic MRI to quantify pelvic organ prolapse (POP) according to the International Continence Society (ICS) using two different reference lines, and to determine which line gives the best concordance with clinical examination.

METHODS

Forty-seven patients with genital prolapse underwent physical examination and dynamic MRI. Five nulliparous, symptom-free female volunteers underwent dynamic MRI as control subjects. Two distinct observers performed the MRI measurements of POP according to the ICS using two distinct reference lines: the mid-pubic line and a new one, the perineal line that provides a better match with the hymen plane. Measurements were repeated twice according to each line. The intra-class coefficient was used to estimate intra-observer and inter-observer reliability; the Altman and Bland plot was used to assess the agreement between MRI and clinical measurements.

RESULTS

The intra-observer and inter-observer reliability of MRI measurements were in general excellent. Intra-class coefficients were better for the mid-pubic line than the perineal line. Although the MRI measurements correlate significantly with the physical measurements, the Altman and Bland plot shows an unacceptable magnitude of discrepancy between clinical and MRI examinations.

CONCLUSIONS

Although dynamic MRI shows excellent inter- and intra-observer reliability, its agreement with clinical examination is poor whatever the line used.

Test-retest reliability of an instrumented speculum for measuring vaginal closure force

AIMS

The study aimed to: a) determine reliability of an instrumented speculum designed for measuring intravaginal closure pressure, and b) compare findings with a comparable device reported in the literature. The goal of these new devices is to reduce subjectivity, improve precision, and acknowledge reliability issues in quantifying levator ani closure force acting on the vagina.

METHODS

The instrumented speculum consisted of two parallel aluminum bills, similar in size to a Peterson speculum. Strain gages located near the root of each bill measure the magnitude of force exerted in the distal vagina. A contraction of the "U-shaped" levator ani muscle closes the levator hiatus with resultant reaction force measured by the speculum in the mid-sagittal plane. We tested the device in twelve nulliparous women making repeated measures within and across 3 different visit days. All measures were made by the same investigator.

RESULTS

Same day measures were repeatable within +/-3.8 N by the third visit, with lesser repeatability on the 1st and 2nd visit days. Across days, repeatability was improved by Visits 2 and 3 with a coefficient of repeatability between those days of +/-5.5 N. Better repeatability was obtained using averaged scores rather than 'best effort' ; but average scores can underestimate best effort.

CONCLUSION

Reasonable within-visit repeatability was found. Across-visit repeatability is consistent with the known difficulty that women have in maximally isolating and activating their levator ani muscles. The results corroborate the repeatability results of Dumoulin et al. [2004] using a similar type of dynamometer.

Racial differences in pelvic floor muscle thickness in asymptomatic nulliparas as seen on magnetic resonance imaging-based three-dimensional color thickness mapping

OBJECTIVE

The objective of the study was to compare levator and obturator thickness between asymptomatic black and white nulliparas using three-dimensional (3D) magnetic resonance imaging (MRI) color mapping.

STUDY DESIGN

3D color-mapped MRI of pelvic muscles were evaluated in 22 similar nulliparas (12 black, 10 white). Levator and obturator (OI) were divided into right and left. Levator was subdivided into puborectalis (PR) and ileococcygeus (IC) portions. Maximal thickness of each muscle was recorded and compared between groups. Nonparametric testing was applied, with significance at P = .05.

RESULTS

Levator thickness was significantly greater in blacks bilaterally (median right PR, 8.5 vs 6.0 mm; P = .001; right IC, 6.5 vs 4.5 mm; P = .002; left PR, 9.5 vs 5.75 mm; P = .0002; left IC, 6.5 vs 5.75 mm; P = .02). Obturator thicknesses were similar (right OI, 20.0 vs 19.5 mm; left OI, 19.25 vs 19.25 mm; P = NS).

CONCLUSION

Significantly thicker levators but similar obturators were seen in black nulliparas, compared with white nulliparas. These levator differences may influence pelvic floor dysfunction risk. The clinical significance of these findings is under study.

Innervation of the levator ani muscles: description of the nerve branches to the pubococcygeus, iliococcygeus, and puborectalis muscles

We described the innervation of the levator ani muscles (LAM) in human female cadavers. Detailed pelvic dissections of the pubococcygeus (PCM), iliococcygeus (ICM), and puborectalis muscles (PRM) were performed on 17 formaldehyde-fixed cadavers. The pudendal nerve and the sacral nerves entering the pelvis were traced thoroughly, and nerve branches innervating the LAM were documented. Histological analysis of nerve branches entering the LAM confirmed myelinated nerve tissue. LAM were innervated by the pudendal nerve branches, perineal nerve, and inferior rectal nerve (IRN) in 15 (88.2%) and 6 (35.3%) cadavers, respectively, and by the direct sacral nerves S3 and/or S4 in 12 cadavers (70.6%). A variant IRN, independent of the pudendal nerve, was found to innervate the LAM in seven (41.2%) cadavers. The PCM and the PRM were both primarily innervated by the pudendal nerve branches in 13 cadavers (76.5%) each. The ICM was primarily innervated by the direct sacral nerves S3 and/or S4 in 11 cadavers (64.7%).

Deformation of the pelvic floor muscles during a vaginal delivery

Pelvic floor dysfunction is a hidden problem with a magnitude unknown to many. Statistics show that one in every ten women will have pelvic floor dysfunction so severe that it will require surgery. Several studies have shown that pelvic floor injuries during a vaginal delivery can be considered a significant factor in the development of urinary incontinence, fecal incontinence, and pelvic organ prolapse. The objective of the present work is to contribute to the clarification of the mechanisms behind pelvic floor disorders related to a vaginal delivery. For this purpose, a numerical simulation based on the finite element method was carried out. The finite element model intends to represent the effects that the passage of a fetal head can induce on the muscles of the pelvic floor, from a mechanical point of view. The model used for the simulation represents the pelvic bones, with the attached pelvic floor muscles and the fetus. In this work, we simulated the movements of the fetus during birth, in vertex position. We simulated the engagement, descent, flexion, internal rotation, and extension of the fetal head. Results for the pelvic floor stretch values obtained during the passage of the fetus head are presented; the deformation field is also shown. The results were obtained using the finite element method and a three-dimensional computer model of the pelvic floor and fetus. The maximum deformation obtained was 0.66 for a vertical displacement of the fetal head of approximately 60 mm.

Finite element studies of the deformation of the pelvic floor

This article describes research involving finite element simulations of women's pelvic floor, undertaken in the engineering schools of Lisbon and Oporto, in collaboration with the medical school of Oporto. These studies are motivated by the pelvic floor dysfunctions that lead namely to urinary incontinence and pelvic organ prolapse. This research ultimately aims at: (i) contributing to clarify the primary mechanism behind such disorders; (ii) providing tools to simulate the pelvic floor function and the effects of its dysfunctions; (iii) contributing to planning and performing surgeries in a more controlled and reliable way. The finite element meshes of the levator ani are based on a publicly available geometric data set, and use triangular thin shell or special brick elements. Muscle and soft tissues are assumed as (quasi-)incompressible hyperelastic materials. Skeletal muscles are transversely isotropic with a single fiber direction, embedded in an isotropic matrix. The fibers considered in this work may be purely passive, or active with input of neuronal excitation and consideration of the muscle activation process. The first assumption may be adequate to simulate passive deformations of the pelvic muscles and tissues (namely, under the extreme loading conditions of childbirth). The latter may be adequate to model faster contractions that occur in time intervals of the same order as those of muscle activation and deactivation (as in preventing urinary incontinence in coughing or sneezing). Numerical simulations are presented for the active deformation of the levator ani muscle under constant pressure and neural excitation, and for the deformation induced by a vaginal childbirth.

Comparison of levator ani muscle defects and function in women with and without pelvic organ prolapse

BACKGROUND

To compare levator ani defects and pelvic floor function among women with prolapse and controls.

METHODS

Levator ani structure and function were measured in a case-control study with group matching for age, race, and hysterectomy status among 151 women with prolapse (cases) and 135 controls with normal support (controls) determined by pelvic organ prolapse quantification examination. Magnetic resonance imaging was used to determine whether there were "major" (more than half missing), "minor" (less than half of the muscle missing), or no defects in the levator ani muscles. Vaginal closure force at rest and during maximal pelvic muscle contraction was measured with an instrumented vaginal speculum.

RESULTS

Cases were more likely to have major levator ani defects than controls (55% compared with 16%), with an adjusted odds ratio of 7.3 (95% confidence interval 3.9-13.6, P<.001) but equally likely to have minor defects (16% compared with 22%). Of women who reported delivery by forceps, 53% had major defects compared with 28% for the nonforceps women, adjusted odds ratio 3.4 (95% confidence interval 1.95-5.78). Women with prolapse generated less vaginal closure force during pelvic muscle contraction than controls (2.0 Newtons compared with 3.2 Newtons P<.001), whereas those with defects generated less force than women without defects (2.0 Newtons compared with 3.1 Newtons, P<.001). The genital hiatus was 50% longer in cases than controls (4.7+/-1.4 cm compared with 3.1+/-1.0 cm, P<.001).

CONCLUSION

Women with prolapse more often have defects in the levator ani and generate less vaginal closure force during a maximal contraction than controls.

LEVEL OF EVIDENCE

II.

Validating a clinical measure of levator hiatus size

OBJECTIVE

We evaluate the interrater reliability of levator hiatus (LH) size and correlate size to other measures of muscle function.

STUDY DESIGN

Participants were examined independently by 2 examiners. During maximal contraction of the levator ani, the muscle was assessed by using Brink's scale. The LH was measured in the transverse and sagittal dimensions by digital palpation. The paired t test was used to compare continuous variables and Spearman's coefficient was used for correlations.

RESULTS

The mean LH transverse was 4.5 cm and the mean LH sagittal was 3 cm. The inter-rater correlation for the LH transverse measurement was 0.6 (P < .01) and 0.8 (P < .01) for the LH sagittal measurement. The correlations between the LH size and Brink's scale were moderate (correlation coefficient -0.4 to -0.5, P < .01). Eighty-three percent of measurements were within 1 cm.

CONCLUSION

This technique for clinical measurement of levator hiatus size shows good interrater reliability.

Effects of pelvic floor muscle contraction on anal canal pressure

The role of pelvic floor muscle contraction in the genesis of anal canal pressure is not clear. Recent studies have suggested that vaginal distension increases pelvic floor muscle contraction. We studied the effects of vaginal distension on anal canal pressure in 15 nullipara asymptomatic women. Anal pressure, rest, and squeeze were measured using station pull-through manometry techniques with no vaginal probe, a 10-mm vaginal probe, and a 25-mm vaginal probe in place. Rest and squeeze vaginal pressures were significantly higher when measured with the 25-mm probe compared with the 10-mm probe, suggesting that vaginal distension enhances pelvic floor contraction. In the presence of the 25-mm vaginal probe, rest and squeeze anal pressures in the proximal part of the anal canal were significantly higher compared with no vaginal probe or the 10-mm vaginal probe. On the other hand, distal anal pressures were not affected by any of the vaginal probes. Ultrasound imaging of the pelvic floor revealed that vaginal distension increased the anterior-posterior length of the puborectalis muscle. Atropine at 15 micro g/kg had no influence on the rest and squeeze anal pressures with or without vaginal distension. Our data suggest that pelvic floor contractions increase pressures in the proximal part of the anal canal, which is anatomically surrounded by the puborectalis muscle. We propose that pelvic floor contraction plays an important role in the fecal continence mechanism by increasing anal canal pressure.

Quantification of levator ani cross-sectional area differences between women with and those without prolapse

OBJECTIVE

Compare levator ani cross-sectional area as a function of prolapse and muscle defect status.

METHODS

Thirty women with prolapse and 30 women with normal pelvic support were selected from an ongoing case-control study of prolapse. For each of the two groups, 10 women were selected from three categories of levator defect severity: none, minor, and major identified on supine magnetic resonance scans. Using those scans, three-dimensional (3D) models of the levator ani muscles were made using a modeling program (3D Slicer), and cross-sections of the pubic portion were calculated perpendicular to the muscle fiber direction using another program, I-DEAS. An analysis of variance was performed.

RESULTS

The ventral component of the levator muscle of women with major defects had a 36% smaller cross-sectional area, and women with minor defects had a 29% smaller cross-sectional area compared with the women with no defects (P < .001). In the dorsal component, there were significant differences in cross-sectional area according to defect status (P = .03); women with major levator defects had the largest cross-sectional area compared with the other defect groups. For each defect severity category (none, minor, major), there were no significant differences in cross-sectional area between women with and those without prolapse.

CONCLUSION

Women with visible levator ani defects on magnetic resonance imaging had significantly smaller cross-sectional areas in the ventral component of the pubic portion of the muscle compared with women with intact muscles. Women with major levator ani defects had larger cross-sectional areas in the dorsal component than women with minor or no defects.

LEVEL OF EVIDENCE

II-2.

Interrater reliability of assessing levator ani muscle defects with magnetic resonance images

The objective of this study is to determine interrater reliability of assessing pubovisceral levator ani muscle defects with magnetic resonance images. Normal pubovisceral muscle was assigned a grade of 0; PVM defects were graded as mild=1 (less than half missing), moderate=2 (more than half missing), and severe=3 (total or near total loss). Among six pairs of examiners, percent agreement and weighted kappa coefficients were calculated to determine agreement between pairs of examiners and among all examiners (i.e., "overall"). For unilateral scoring, exact agreement was found in 83.7%, and differences of one, two, and three grades were found in 14.7, 1.5, and 0.1%, respectively. For bilateral scoring, exact agreement and differences of one, two and three grades were found in 75.4, 15.9, 6.9, and 1.6%, respectively. Thus, exact agreement or a one-point difference was reached in 91.3% of cases. When defect status was categorized as none/normal, minor, and major, the overall weighted kappa coefficient was 0.86 (95% CI 0.83, 0.89). There was variation among examiner pairs with unilateral (p=0.002) and bilateral (p=0.02) scoring, but not when defect status was categorized as none/normal, minor, and major (p=0.59). There was agreement to within one point in 91% of cases when six examiner pairs scored levator ani defects on a seven-point scale. Examiner pairs discriminated injury similarly when defect status was categorized as normal/none, minor, or major.