Modelling of Soft Connective Tissues to Investigate Female Pelvic Floor Dysfunctions

Quantifying the effects of five rehabilitation training methods on the ability of elderly men to control bowel movements: a finite element analysis study

Purpose

The study aims to develop a finite element model of the pelvic floor and thighs of elderly men to quantitatively assess the impact of different pelvic floor muscle trainings and the urinary and defecation control ability.

Methods

A finite element model of the pelvic floor and thighs of elderly men was constructed based on MRI and CT. Material properties of pelvic floor tissues were assigned through literature review, and the relative changes in waistline, retrovesical angle (RVA) and anorectad angulation (ARA) to quantitatively verify the effectiveness of the model. By changing the material properties of muscles, the study analyzed the muscle strengthening or impairment effects of the five types of rehabilitation training for four types of urination and defecation dysfunction. The changes in four outcome indicators, including the retrovesical angle, anorectad angulation, stress, and strain, were compared.

Results

This study indicates that ARA and RVA approached their normal ranges as material properties changed, indicating an enhancement in the urinary and defecation control ability, particularly through targeted exercises for the levator ani muscle, external anal sphincter, and pelvic floor muscles. This study also emphasizes the effectiveness of personalized rehabilitation programs including biofeedback, exercise training, electrical stimulation, magnetic stimulation, and vibration training and advocates for providing optimized rehabilitation training methods for elderly patients.

Discussion

Based on the results of computational biomechanics, this study provides foundational scientific insights and practical recommendations for rehabilitation training of the elderly's urinary and defecation control ability, thereby improving their quality of life. In addition, this study also provides new perspectives and potential applications of finite element analysis in elderly men, particularly in evaluating and designing targeted rehabilitation training.

In silico prediction of maximum perineal muscle strain during vaginal delivery by design of experiment

BACKGROUND AND OBJECTIVE

The prevalence of pelvic floor muscle injuries induced by childbirth is higher than 23 % in the general women population. Such injuries can lead to prolapses and other pathologies in future female life. Leveraging computational biomechanics, the study implements an advanced female pelvic floor model for computing the maximum pelvic muscle strain, which serves as an injury risk indicator. The design of experiment method, abbreviated as DoE, is used to compute the maximum strain for boundary values of bony pelvis dimensions, namely the anterior-posterior diameter (abbreviated as APD) and the transverse diameter (abbreviated as TD). This is done in combination with small, medium and large percentiles of fetal head circumference (abbreviated as HC).

METHODS

We utilized a previously developed finite element model of a female pelvic floor, as a reference, and enhanced it with new features, including a more detailed tissue geometry and advanced constitutive material models. The APD and TD dimensions were sourced from the set of MRI of 64 nulliparous women. This data was used to estimate the boundary dimensions of the female bony pelvis, combining both small and large values of APD and TD. Together with the 10th and the 95th percentiles for HC, a three-dimensional domain was constructed to assess the maximum pelvic muscle strain. In boundary cases, the maximum pelvic muscle strain was computed across 8 full-factorial design models (each situated at one corner of the domain, thereby combining the minimum and the maximum values of APD, TD and HC). This was done to define a response surface that predicts the maximum pelvic muscle strain within the domain. The accuracy of this response surface prediction was validated using 15 additional intermediate design models. These models were placed at the center of the domain (1 point), the centres of the domain boundary surfaces (6 points), and midway along each domain boundary edge (8 points).

RESULTS

The maximum strain results for 8 combinations of APD, TD, and HC were employed to construct a linear response surface as a function of APD, TD, and HC. Tests at an additional 19 domain points served to evaluate the efficiency of the response surface prediction. The response surface demonstrated strong predictability, with an absolute average error of 1.52 %, an absolute median error of 1.52 %, and an absolute maximum error of 11.11 %. HC emerged as the most influencing dimension, accounting for 16 % of influence.

CONCLUSIONS

The reference finite element pelvic floor model was scaled to 8 full-factorial female-specific pelvic floor models, which represent the combination of boundary values for APD, TD, and HC. The maximum pelvic floor muscle strain from these 8 models was used to design a response surface. When implementing the DoE approach to construct the response, there was consistent predictability for the maximum perineal muscle strain, as validated by the additional 19 intermediate design models. As a result, the response surface methodology can serve as an initial predictor for potential childbirth-induced pelvic floor muscle injury.

Anatomical investigation of the pelvic urogenital fascia in 10 formalin-fixed female cadavers: novel insights into the laparoscopic total mesometrial resection

PURPOSE

Previous anatomical studies of the urogenital fascia (UGF) have focused on males, and there is a lack of relevant anatomical studies on the distribution of the extraperitoneal UGF in females.

METHODS

In this investigation, guided by the embryonic development of the female urogenital system, the ventral pelvic fascia structure of 10 female cadavers was dissected, and the distribution and morphology of female extraperitoneal UGF were observed, recorded in text, photographs and video, and 3D modeling was performed.

RESULTS

We find that in the female extraperitoneal space there is a migratory fascial structure, the UGF, which surrounds the urogenital system and extends from the perinephric region to the pelvis along with the development of the urogenital organs. The two layers of the UGF are composed of loose connective tissue rich in fat that surrounds the urogenital organs, their accessory vascular structures, and the nerves of the abdominopelvic cavity. In the pelvis, it participates in the formation of the ligamentous structures around the rectum and uterus. Finally, it surrounds the bladder and gradually moves into the loose connective tissue of the medial umbilical fold.

CONCLUSIONS

Sorting out the distribution characteristics of UGF has some reference value for studying the metastasis of gynecological tumors, the biomechanical structure of the female pelvis, and the surgical methods of gynecology, colorectal surgery, and hernia surgery.

Small Extracellular Vesicles Secreted by Peri-urethral Tissues Regulate Fibroblast Function and Contribute to the Pathogenesis of Female Stress Urinary Incontinence

OBJECTIVE

This study aimed to explore the existence of small extracellular vesicles (sEVs) in peri-urethral tissues and the role of abnormal expression of sEVs in the pathogenesis of female stress urinary incontinence (SUI).

METHODS

sEVs were extracted from peri-urethral vaginal wall tissues using differential centrifugation and were observed by transmission electron microscopy (TEM). The number of sEVs and their protein contents were compared between SUI and control groups using nanoparticle tracking analysis (NTA) and bicinchoninic acid (BCA) protein assay. Fibroblasts were cultured separately with SUI (SsEVs group) and normal tissue sEVs (NsEVs group). Proliferation and migration of fibroblasts were compared between groups using CCK-8 and wound healing assays, respectively. Expression levels of collagen I and III were compared among blank control (BC), NsEVs, and SsEVs groups using real-time PCR. Protein mass spectrometry was used to test the differentially expressed proteins contained in sEVs between groups.

RESULTS

sEVs were extracted and found under the electron microscope. There were significantly more sEVs extracted from the SUI group compared to the normal group. Fibroblasts showed increased proliferative and decreased migratory abilities, and expressed more collagen in the SsEVs group compared to the NsEVs and BC groups. Protein spectrum analysis demonstrated several differentially expressed targets, including components of microfibrils, elastin polymer, and anti-inflammatory factors.

CONCLUSION

sEVs were detected in the peri-urethral tissues. SUI tissues expressed more sEVs than control. The abnormal expression of sEVs and their protein contents may contribute to the pathogenesis and progression of SUI.

Creation of the biomechanical finite element model of female pelvic floor supporting structure based on thin-sectional high-resolution anatomical images

PURPOSE

The main purpose of this study is to obtain a finite element biomechanical model that accurately mimics pelvic organ prolapse in women, to study pelvic floor supporting structures' biomechanical properties and function. We used thin-sectional high-resolution anatomical images (Chinese Visible Human, CVH) to reconstruct a detailed three-dimensional (3D) biomechanical finite element model of the female pelvic floor supporting structure including cardinal ligament, uterosacral ligament, levator ani muscle (LAM) and perianal body. The Valsalva maneuver was simulated by loading the uterus and bladder with a pressure increasing from 0 to 10 kPa. The stress, strain and displacement of supporting structures were calculated. The cardinal ligament, the uterosacral ligament and the LAM were stressed greatly when the uterus moved downward, and the maximum stress could reach 0.267 MPa, 1.51 MPa and 0.065 MPa respectively, and the maximum strain could reach 0.154, 0.16, 0.265, and the maximum displacement could reach 1.786 cm, 1.946 cm and 0.567 cm. Displacement of the perineal body also occurred, and its stress, strain and displacement were 0.092 MPa, 0.381, 0.73 cm. The stress, strain and displacement of the supporting structure around the urethra were 0.339 MPa, 0.169, 1.491 cm. Our model based on CVH has more detailed anatomical structures, which is superior to that based on MRI. Our simulation results were consistent with previous findings, which verified the unbalance of abdominal pressure and pelvic floor supporting structures will lead to POP, which provide a theoretical basis for pelvic floor anatomy and function as well as obstetrical surgery.

Distinctive structure, composition and biomechanics of collagen fibrils in vaginal wall connective tissues associated with pelvic organ prolapse

Collagen is the predominant structural protein within connective tissues. Pelvic organ prolapse (POP) is characterized by weakening of the pelvic floor connective tissues and loss of support for pelvic organs. In this study, we examined the multiscale structure, molecular composition and biomechanics of native collagen fibrils in connective tissues of the posterior vaginal fornix collected from healthy women and POP patients, and established the correlation of these properties with clinical POP quantification (POP-Q) scores. The collagen characteristics, including collagen amount, ratio of Collagen I and Collagen III, collagen fibril d-period, alignment and stiffness, were found to change progressively with the increase of the clinical measurement of Point C, a measure of uterine descent and apical prolapse. The results imply that a severe prolapse is associated with stiffer collagen fibrils, reduced collagen d-period, increased fibril alignment and imbalanced collagen synthesis, degradation and deposition. Additionally, prolapse progression appears to be synchronized with deterioration of the collagen matrix, suggesting that a POP-Q score obtained via a non-invasive clinical test can be potentially used to quantitatively assess collagen abnormality of a patient's local tissue. STATEMENT OF SIGNIFICANCE: Abnormal collagen metabolism and deposition are known to associate with connective tissue disorders, such as pelvic organ prolapse. Quantitative correlation of the biochemical and biophysical characteristics of collagen in a prolapse patient's tissue with the clinical diagnostic measurements is unexplored and unestablished. This study fills the knowledge gap between clinical prolapse quantification and the individual's cellular and molecular disorders leading to connective tissue failure, thus, provides the basis for clinicians to employ personalized treatment that can best manage the patient's condition and to alert pre-symptomatic patients for early management to avoid unwanted surgery.

Impact of treatment modality on pelvic floor dysfunction among uterine cancer survivors

OBJECTIVE

Pelvic floor dysfunction is a common adverse effect of uterine cancer treatment. In this study we compared patient-reported outcomes regarding pelvic floor dysfunction among uterine cancer survivors after hysterectomy and bilateral salpingo-oophorectomy, surgery and brachytherapy, or surgery and external beam radiotherapy with or without brachytherapy versus women who had a hysterectomy for benign indications.

METHODS

We used the validated 20-item Pelvic Floor Distress Inventory to assess lower urinary distress, colorectal distress, and pelvic organ prolapse dysfunction in each treatment group. Pelvic floor dysfunction-related quality of life in these domains was compared across treatment modalities using the Pelvic Floor Impact Questionnaire-7. Treatment type, body mass index, comorbidities, and number of vaginal births were obtained from medical records. A zero-inflated negative binomial regression model was used to assess the association of treatment regimens and covariates relative to the non-cancer cohort.

RESULTS

A total of 309 surveys were analyzed. The median age of the patients at surgery was 58 years (range 20-87) and the median age at survey completion was 66 years (range 34-92). Most participants reported experiencing at least one symptom of pelvic floor dysfunction (76% by Pelvic Floor Distress Inventory-2). The type of treatment had no effect on overall pelvic floor dysfunction on multivariate analysis (all p>0.05). Worse urinary-related symptoms were associated with higher body mass index at surgery (OR 1.41), higher age at time of survey (OR 1.07), and higher numbers of vaginal births (OR 1.43) (all p<0.05).

CONCLUSIONS

Overall, pelvic floor dysfunction did not significantly vary by treatment modality. Our findings suggest complex interactions among age, body mass index, and parity as to how uterine cancer treatment affects pelvic floor quality of life, which should be considered in the choice of treatment strategy and patient counseling.

Simulation of vaginal uterosacral ligament suspension damage, mimicking a mesh-augmented apical prolapse repair

Synthetic implants were used for repair of anterior compartment prolapses, which can be caused by direct trauma resulting in damaged pelvic structures. The mechanical properties of these implants may cause complications, namely erosion of the mesh through the vagina. In this study, we evaluated, by modeling, the behavior of implants, during Valsalva maneuver, used to replace damaged uterosacral ligaments (USLs), mimicking a sacrocolpopexy repair. For this purpose, two synthetic implants (A®, for prolapse repair and B®, for Hernia repair) were uniaxially tested, and the mechanical properties obtained were incorporated in the computational models of the implants. The computational model for the implant was incorporated into the model of the female pelvic cavity, in order to mimic the USLs after its total rupture and with 90% and 50% impairment. The total rupture and impairments of the USLs, caused a variation of the supero-inferior displacement and displacement magnitude of the vagina, with higher values for the total rupture. With total rupture of the USLs, when compared to healthy USLs, supero-inferior displacement and displacement magnitude of the vagina increased by 4.98 mm (7.69 mm vs 12.67 mm) and 6.62 mm (9.38 mm vs 16.00 mm), respectively. After implantation (A® and B®) a reduction of the supero-inferior displacements of the anterior vaginal wall occurred, to values found in the case of the model without any impairment or rupture of the ligaments. The simulation was able to mimic the biomechanical response of the USLs, in response to different implants stiffnesses, which can be used in the development of novel meshes.

The evolution of pelvic canal shape and rotational birth in humans

BACKGROUND

The human foetus typically needs to rotate when passing through the tight birth canal because of the complex shape of the pelvis. In most women, the upper part, or inlet, of the birth canal has a round or mediolaterally oval shape, which is considered ideal for parturition, but it is unknown why the lower part of the birth canal has a pronounced anteroposteriorly oval shape.

RESULTS

Here, we show that the shape of the lower birth canal affects the ability of the pelvic floor to resist the pressure exerted by the abdominal organs and the foetus. Based on a series of finite element analyses, we found that the highest deformation, stress, and strain occur in pelvic floors with a circular or mediolaterally oval shape, whereas an anteroposterior elongation increases pelvic floor stability.

CONCLUSIONS

This suggests that the anteroposterior oval outlet shape is an evolutionary adaptation for pelvic floor support. For the pelvic inlet, by contrast, it has long been assumed that the mediolateral dimension is constrained by the efficiency of upright locomotion. But we argue that the mediolateral elongation has evolved because of the limits on the anteroposterior diameter imposed by upright posture. We show that an anteroposteriorly deeper inlet would require greater pelvic tilt and lumbar lordosis, which compromises spine health and the stability of upright posture. These different requirements of the pelvic inlet and outlet likely have led to the complex shape of the pelvic canal and to the evolution of rotational birth characteristic of humans.

Uterus Modeling from Cell to Organ Level: towards Better Understanding of Physiological Basis of Uterine Activity

The relatively limited understanding of the physiology of uterine activation prevents us from achieving optimal clinical outcomes for managing serious pregnancy disorders such as preterm birth or uterine dystocia. There is increasing awareness that multi-scale computational modeling of the uterus is a promising approach for providing a qualitative and quantitative description of uterine physiology. The overarching objective of such approach is to coalesce previously fragmentary information into a predictive and testable model of uterine activity that, in turn, informs the development of new diagnostic and therapeutic approaches to these pressing clinical problems. This article assesses current progress towards this goal. We summarize the electrophysiological basis of uterine activation as presently understood and review recent research approaches to uterine modeling at different scales from single cell to tissue, whole organ and organism with particular focus on transformative data in the last decade. We describe the positives and limitations of these approaches, thereby identifying key gaps in our knowledge on which to focus, in parallel, future computational and biological research efforts.

A Preliminary Study on Quantitative Quality Measurements of the Urethral Rhabdosphincter Muscle by Supersonic Shear Wave Imaging in Women With Stress Urinary Incontinence

OBJECTIVES

To quantitatively assess the quality of the urethral rhabdosphincter muscle by measuring its shear wave velocity (V_s ) and calculating the Young modulus (E) with supersonic shear wave imaging (SSI).

METHODS

This was a prospective study of 43 women with SUI and 52 female control participants who underwent a transperineal US examination with SSI. Supersonic shear wave imaging was performed at rest with a linear transducer and a specialized-preset procedure. The stability and validity of the shear waves were automatically assessed by the SSI procedure. The SSI images were visualized in a color-coded elastographic image. In the postprocessing analysis, the ventral part of the urethral rhabdosphincter muscle was manually outlined. The mean V_s and the mean E of the muscle were measured by the SSI procedure. The relationship between the mean V_s , mean E, and SUI was evaluated.

RESULTS

The SSI examination was successfully performed in 40 patients with SUI (93.0%) and 40 female control participants (76.9%). No significant differences between the groups in age, body mass index, and parity were identified. For the SUI and control groups, the mean V_s values were 2.54 and 2.73 m/s, respectively, and the mean E values were was 19.7 and 22.7kPa. Significant correlations were found between SUI and the mean V_s as well as the mean E (Spearman correlation coefficients, -0.41 and -0.43; P < .05).

CONCLUSIONS

The mechanical properties of the urethral sphincter can be quantitatively assessed by SSI. The stiffness of the urethral rhabdosphincter muscle was significantly lower in women with SUI.

A computational analysis of the effect of supporting organs on predicted vesical pressure in stress urinary incontinence

Stress urinary incontinence (SUI) or urine leakage from urethra occurs due to an increase in abdominal pressure resulting from stress like a cough or jumping height. SUI is more frequent among post-menopausal women. In the absence of bladder contraction, vesical pressure exceeds urethral pressure leading to urine leakage. The main aim of this study is to utilize fluid-structure interaction techniques to model bladder and urethra computationally under an external pressure like sneezing. Both models have been developed with linear elastic properties for the bladder wall while the patient model has also been simulated utilizing the Mooney-Rivlin solid model. The results show a good agreement between the clinical data and the predicted values of the computational models, specifically the pressure at the center of the bladder. There is 1.3% difference between the predicted vesical pressure and the vesical pressure obtained from urodynamic tests. It can be concluded that the accuracy of the predicted pressure in the center of the bladder is significantly higher for the simulation assuming nonlinear material property (hyperelastic) for the bladder in comparison to the accuracy of the linear elastic model. The model is beneficial for exploring treatment solutions for SUI disorder. Graphical abstract ^{3D processing of bladder deformation during abdominal pressure of a the physiological model and b the pathological model (starting from left to right and up to down, consecutively)}.