Biomechanical Mapping of the Female Pelvic Floor: Prolapse versus Normal Conditions

The impact of short-term pelvic floor muscle training on the biomechanical parameters of the pelvic floor among patients with stress urinary incontinence: A pilot study

OBJECTIVE

Our study aimed to improve the understanding of the biomechanical changes occurring in the pelvic floor due to pelvic floor muscle training (PFMT), which is responsible for improving stress urinary incontinence (SUI) symptoms.

STUDY DESIGN

In this prospective cohort study, we examined the impact of a six-week PFMT program in women with stress or stress-predominant urinary incontinence on the biomechanical parameters of the pelvic floor. Fifty-two biomechanical parameters were measured by Vaginal Tactile Imager (VTI) at baseline and at a six-week follow-up. In addition, we have assessed the Urinary Distress Inventory (UDI-6), Incontinence Impact Questionnaire (IIQ-7), and Patient's Global Impression of Severity (PGI-S) scores at enrolment and at six-week follow-up. We have divided our cohort into two groups, Improved Group (IG) and Not-improved Group (NIG), based on the change in UDI-6 score after six weeks and compared the biomechanical changes within and between the two groups.

RESULTS

The overall cohort included twenty women with stress or stress-predominant SUI based on MESA questionnaire [MESA SUI index (mean ± SD) 63.3 % ± 24.0 %, MESA UUI index (mean ± SD) 13.3 % ± 15.3 %, p < 0.01]. Nine of the 52 VTI parameters have changed significantly after six weeks of PFMT in the entire cohort. Eleven women (IG) achieved the minimum 11-point change in the UDI-6 scaled score. In IG, we found that three VTI parameters differed significantly: Parameter 1: the maximum value of force measured during the VTI probe insertion [(N, mean ± SD) 0.55 ± 0.18 vs. 0.78 ± 0.31, p < 0.049], parameter 18: the maximum gradient at the upper third of the vagina (posterior) [(kPa/mm, mean ± SD) 0.16 ± 0.05 vs. 0.36 ± 0.28, p < 0.048], and parameter 47: integral force change in the anterior compartment at reflex pelvic muscle contraction (cough) [(N, mean ± SD) 1.61 ± 0.85 vs. 1.97 ± 0.71, p < 0.045].

CONCLUSION

Our study revealed a significant association between the improvement of strength in targeted muscle groups and a reduction in urinary incontinence symptoms. Identifying specific muscles changing PFMT provides valuable insights for specific interventions. Our findings may help to create personalized and targeted interventions to improve the quality of life of women affected by SUI.

Biomechanical Integrity Score of the Female Pelvic Floor for Stress Urinary Incontinence

INTRODUCTION AND HYPOTHESIS

This study is aimed at developing and validating a new integral parameter, the Biomechanical Integrity score (BI-score) of the female pelvic floor for stress urinary incontinence conditions.

METHODS

A total of 130 subjects were included in the observational cohort study; 70 subjects had normal pelvic floor conditions, and 60 subjects had stress urinary incontinence (SUI). A Vaginal Tactile Imager (VTI) was used to acquire and automatically calculate 52 biomechanical parameters for eight VTI test procedures (probe insertion, elevation, rotation, Valsalva maneuver, voluntary muscle contractions in two planes, relaxation, and reflex contraction). Statistical methods were applied (t test, correlation) to identify the VTI parameters sensitive to the pelvic SUI conditions.

RESULTS

Twenty-seven parameters were identified as statistically sensitive to SUI development. They were subdivided into five groups to characterize tissue elasticity (group 1), pelvic support (group 2), pelvic muscle contraction (group 3), involuntary muscle relaxation (group 4), and pelvic muscle mobility (group 5). Every parameter was transformed to its standard deviation units using the dataset for normal pelvic conditions, similar to the T-score for bone density. Linear combinations with specified weights led to the composition of five component parameters for groups 1-5 and to the BI-score in standard deviation units. The p value for the BI-score has p = 4.0 × 10-28 for SUI versus normal conditions.

CONCLUSIONS

Quantitative transformations of the pelvic tissues, support structures, and functions under diseased conditions may be studied with the SUI BI-score in future research and clinical applications.

Analysis of the anatomical and biomechanical characteristics of the pelvic floor in cystocele

INTRODUCTION

Stress urinary incontinence (SUI) occurs due to disruption of the pelvic floor anatomy; however, the complexity of the pelvic floor support structures and individual patient differences make it difficult to identify the weak points in the pelvic floor support that cause SUI to occur, develop, and recur. This study aimed to analyze the pelvic floor anatomy, structural features, and biomechanics of cystoceles to develop more effective treatment plans with individualized and precise healthcare.

MATERIAL AND METHODS

In this observational case-controlled study (clinical trial identifier BOJI201855L), 102 women with normal pelvic floor function and 273 patients diagnosed with cystocele degrees I-III were identified at Shanghai General Hospital from October 2016 to December 2019. We combined ultrasound and vaginal tactile imaging (VTI) to assess the anatomy and biomechanical functions of the anterior and posterior vaginal walls. Both examinations included relaxation and muscle tension tests.

RESULTS

Of the 42 VTI parameters, 13 were associated with the degree of cystocele, six with an increase in the urethral rotation angle (pointing to the mobility of the urethra), and six with a decrease in the retrovesical angle (pointing to hypsokinesis and decrease in bladder position). According to these data, the strength of tissues, especially the muscles in both the anterior and posterior compartments, contributes to the stability of the pelvic floor structure. The strength of the levator ani muscle (LAM) is important for the degree of cystocele, mobility of the urethra, hypsokinesis, and decrease in bladder position.

CONCLUSIONS

In general, the biomechanical status of the pelvic floor in patients with cystocele is complex and involves various muscles, ligaments, tendons, and fascia. Of these, repair and exercise of the LAM have not received much attention in the treatment of patients with cystoceles, which may be an important risk factor for the high recurrence rate.

Correlation between the female pelvic floor biomechanical parameters and the severity of stress urinary incontinence

BACKGROUND

Stress urinary incontinence (SUI) is a common condition that requires proper evaluation to select a personalized therapy. Vaginal Tactile Imaging (VTI) is a novel method to assess the biomechanical parameters of the pelvic floor.

METHODS

Women with SUI were enrolled in this cross-sectional study. Participants completed the Medical, Epidemiologic, and Social Aspects of Aging (MESA) questionnaire and the Patient Global Impression of Severity Question (PGI-S) and underwent a VTI examination. Based on the MESA and PGI-S questionnaires, participants were divided into mild, moderate, and severe SUI groups. Fifty-two biomechanical parameters of the pelvic floor were measured by VTI and compared between the groups (mild vs. moderate and severe). SUI Score and Index were calculated from the MESA questionnaire. Pearson correlation was used to determine the strength of association between selected VTI parameters and the MESA SUI Index and MESA SUI Score.

RESULTS

Thirty-one women were enrolled into the study. Significant differences were observed in the VTI parameters 16, 22-24, 38, 39 when the difference between mild and severe subgroups of SUI based on the PGI-S score was examined. Parameter 16 refers to the maximum gradient at the perineal body, parameter 22-24 refers to the pressure response of the tissues behind the vaginal walls, and parameter 38, 39 refers the maximum pressure change and value on the right side at voluntary muscle contraction. VTI parameter 49, describing the displacement of the maximum pressure peak in the anterior compartment, showed a significant difference between the mild SUI and the moderate-severe SUI according to the MESA SUI score (mean ± SD 14.06 ± 5.16 vs. 7.54 ± 7.46, P = 0.04). The MESA SUI Index and SUI Score displayed a positive correlation concerning VTI parameters 4 (the maximum value of the posterior gradient) and 27 (the displacement of the maximum pressure peak in the anterior compartment) (VTI4 vs. MESA SUI Index r = 0.373, P = 0.039; VTI4 vs. MESA SUI Score r = 0.376, P = 0.037; VTI27 vs. MESA SUI Index r = 0.366, P = 0.043; VTI27 vs. MESA SUI Score r = 0.363, P = 0.044).

CONCLUSIONS

Female pelvic floor biomechanical parameters, as measured by VTI, correlate significantly with the severity of SUI and may help guide therapeutic decisions.

Biomechanical integrity score of the female pelvic floor

INTRODUCTION AND HYPOTHESIS

The aim of this study is to develop and validate a new integral parameter, the Biomechanical Integrity score (BI-score), for the characterization of the female pelvic floor.

METHODS

A total of 253 subjects with normal and pelvic organ prolapse (POP) conditions were included in the multi-site observational, case-control study; 125 subjects had normal pelvic floor conditions, and 128 subjects had POP stage II or higher. A Vaginal Tactile Imager (VTI) was used to acquire and automatically calculate 52 biomechanical parameters for eight VTI test procedures (probe insertion, elevation, rotation, Valsalva maneuver, voluntary muscle contractions in two planes, relaxation, and reflex contraction). Statistical methods were applied (t-test, correlation) to identify the VTI parameters sensitive to the pelvic conditions.

RESULTS

Twenty-six parameters were identified as statistically sensitive to POP development. They were subdivided into five groups to characterize (1) tissue elasticity, (2) pelvic support, (3) pelvic muscle contraction, (4) involuntary muscle relaxation, and (5) pelvic muscle mobility. Every parameter was transformed to its standard deviation units against the patient age similar to T-score for bone density. Linear combinations with specified weights led to the composition of five component parameters for groups (1)-(5) and the BI-score in standard deviation units. The p-value for the BI-score has p = 4.3 × 10-31 for POP versus normal conditions. A reference BI-score curve against age for normal pelvic floor conditions was defined.

CONCLUSIONS

Quantitative transformations of the pelvic tissues, support structures, and functions under diseased conditions may be studied with the BI-score in future research and practical applications.

The impact of radiation therapy on vaginal biomechanical properties

OBJECTIVE

In women with cervical cancer (CC), treatment with radiation causes changes in vaginal biomechanical properties, anatomy and function. The aims of the current study were to objectively assess effects of radiotherapy (RT) on vaginal elasticity, wall mobility and contraction strength; and to evaluate associations of these changes with sexual function.

STUDY DESIGN

This prospective cohort study was approved by our Institutional Review Board. Between May 2018 and June 2020, women with CC who were candidates for RT were eligible to participate. Participants underwent vaginal tactile imaging (VTI) evaluation and were asked to fill the Female Sexual Function Index (FSFI) questionnaire at the time of first RT session and at a 6-month post-treatment follow up visit. Women who underwent radical hysterectomy, or had pelvic side-wall, pelvic or distant organ metastasis were not included.

RESULTS

A total of 25 women with locally advanced CC were included in the final analysis. The mean age was 39 ± 2.7 years, the mean BMI was 24.8 ± 2.2 kg/m² and the median parity was 2 (range: 1-5). Following RT, the mean scores for vaginal elasticity and vaginal tightening were significantly lower than at pre-treatment: 11.3 ± 2.5 vs. 28.3 ± 9, P < 0.0001 and 2.6 ± 0.7 vs. 16.7 ± 3, P < 0.0001, respectively. Following RT, significant decreases were demonstrated in vaginal wall mobility and pelvic muscle contraction strength: from 1.77 ± 0.34 to 0.36 ± 0.15, P < 0.0001 and from 2.55 ± 0.48 to 0.52 ± 0.23, P < 0.0001, respectively. Compared to pre-treatment, post-RT vaginal length was significantly shorter (3.30 ± 0.22 vs. 7.64 ± 0.63, P = 0.0023) and sexual intercourse frequency significantly lower: 1 (range 1-2) vs. 2 (range 1-4), P = 0.014). The mean total FSFI score was significantly lower following RT (6.7 ± 1 vs. 14.5 ± 2.7, P < 0.0001).

CONCLUSIONS

Women with locally advanced CC who have been treated with RT exhibit persistent vaginal biomechanical changes that compromise sexual activity and result in considerable distress.

Tactile and Ultrasound Image Fusion for Functional Assessment of the Female Pelvic Floor

INTRODUCTION

The true etiology of pelvic organ prolapse and urinary incontinence and variations observed among individuals are not entirely understood. Tactile (stress) and ultrasound (anatomy, strain) image fusion may furnish new insights into the female pelvic floor conditions. This study aimed to explore imaging performance and clinical value of vaginal tactile and ultrasound image fusion for characterization of the female pelvic floor.

METHODS

A novel probe with 96 tactile and 192 ultrasound transducers was designed. Women scheduled for a urogynecological visit were considered eligible for enrollment to observational study. Intravaginal tactile and ultrasound images were acquired for vaginal wall deformations at probe insertion, elevation, rotation, Valsalva maneuver, voluntary contractions, involuntary relaxation, and reflex pelvic muscle contractions. Biomechanical mapping has included tactile/ultrasound imaging and functional imaging.

RESULTS

Twenty women were successfully studied with the probe. Tactile and ultrasound images for tissues deformation as well as functional images were recorded. Tactile (stress) and ultrasound (strain) images allowed creation of stress-strain maps for the tissues of interest in absolute scale. Functional images allowed identification of active pelvic structures and their biomechanical characterization (anatomical measurements, contractive mobility and strength). Fusion of the modalities has allowed recognition and characterization of levator ani muscles (pubococcygeal, puborectal, iliococcygeal), perineum, urethral and anorectal complexes critical in prolapse and/or incontinence development.

CONCLUSIONS

Vaginal tactile and ultrasound image fusion provides unique data for biomechanical characterization of the female pelvic floor. Bringing novel biomechanical characterization for critical soft tissues/structures may provide extended scientific knowledge and improve clinical practice.

Predictive Value of Biomechanical Mapping for Pelvic Organ Prolapse Surgery

OBJECTIVE

This study examined biomechanical changes in pelvic floor after urogynecological surgery.

METHODS

This multisite clinical study was designed to explore changes in tissue elasticity, pelvic support, and certain functions (contractive strength, muscle relaxation speed, muscle motility) after pelvic organ prolapse (POP) surgery. A biomechanical mapping of the pelvic floor was performed before and 4 to 6 months after the surgery. The biomechanical data for 52 parameters were acquired by vaginal tactile imaging for manually applied deflection pressures to vaginal walls and pelvic muscle contractions. The two-sample t-test (P < 0.05) was used to test the null hypothesis that presurgery data in group 1 (positive parameter change after surgery) and presurgery data in group 2 (negative parameter change after surgery) belonged to the same distribution.

RESULTS

A total of 78 subjects with 255 surgical procedures were analyzed across 5 participating clinical sites. All 52 t-tests for group 1 versus group 2 had P value in the range from 4.0 × 10-10 to 4.3 × 10-2 associating all of the 52 parameter changes after surgery with the presurgical conditions. The P value of before and after surgery correlation ranged from 3.7 × 10-18 to 1.6 × 10-2 for 50 of 52 tests, with Pearson correlation coefficient ranging from -0.79 to -0.27. Thus, vaginal tactile imaging parameters strongly correlated weak pelvic floor presurgery with the positive POP surgery outcome of improved biomechanical properties.

CONCLUSIONS

Pelvic organ prolapse surgery, in general, improves the biomechanical conditions and integrity of the weak pelvic floor. The proposed biomechanical parameters can predict changes resulting from POP surgery.

The impact of vaginal hysterectomy and uterosacral ligament suspension on vaginal elasticity and sexual function

OBJECTIVE

Hysterectomy for benign indications has profound effects on both anatomical and physiological pelvic floor and vaginal properties. Vaginal tactile imaging (VTI) enables the quantification of pelvic floor and vaginal biomechanical properties; this enables objective evaluation of various pelvic floor functions. The purposes of this study were to evaluate via VTI, the changes in vaginal elasticity, mobility and strength, before and after hysterectomy by transvaginal natural orifice transluminal endoscopic surgery (vNOTES) and high utero-sacral ligament suspension (USLS); and to assess associations with sexual function. The objective of the current study was to evaluate the effect of these procedures on vaginal elasticity and sexual function.

STUDY DESIGN

This prospective cohort study included women who underwent hysterectomy by vNOTES and USLS for the treatment of pelvic organ prolapse (POP). All the women underwent both pre- and postoperative VTI and sexual function evaluation. Vaginal elasticity and wall mobility, and the contraction strength and tone of levator muscles, were measured prior to and 6 months following surgery using VTI.

RESULTS

A total of 23 women, mean age 56.5 years, with stage 3-4 POP participated. Vaginal elasticity increased from 27.3 ± 8.8 to 34.8 ± 12 (P < 0.05) and Female Sexual Function Index (FSFI) scores increased from 22.17 ± 1.62 to 28.66 ± 1.51 (P < 0.05). No correlation was observed between these results. A statistically significant decrease in the mobility of the anterior vaginal wall was demonstrated, from 7.98 ± 10.6 to 0.83 ± 7.5 (P < 0.0001).

CONCLUSIONS

VTI showed improvements in vaginal elasticity, mobility and FSFI scores following hysterectomy and POP repair performed by vNOTES.

Characterization of Perineum Elasticity and Pubic Bone-Perineal Critical Distance with a Novel Tactile Probe: Results of an Intraobserver Reproducibility Study

BACKGROUND

Tactile imaging provides biomechanical mapping of soft tissues. Objective biomechanical and anatomical assessment of critical structures within the vagina and pelvis may allow development and validation of a clinical tool that could assist with clinical decisions regarding obstetrical procedures and mode of delivery. Objective: To assess intraobserver reproducibility of measurements of perineal elasticity and pubic bone-perineal critical distance with a novel tactile probe in pregnant women.

METHODS

An Antepartum Tactile Imager (ATI) was designed with a vaginal probe resembling a fetal skull. The probe comprises 128 tactile sensors on a double curved surface and measures 46 mm in width and 72 mm in length. The probe has a motion tracking sensor that allows acquisition of 3D tactile images. There were two arms of the study. In the first arm, biomechanical mapping of the perineum and pelvic bone location was performed in 10 non-pregnant women for purposes of demonstrating safety and feasibility. In the second arm, biomechanical mapping was performed in 10 pregnant women to explore intraobserver reproducibility. Each subject had two standardized examinations over 3 - 5 minutes by the same observer. Examination comfort and pain levels were assessed by post-procedure survey. Reproducibility was analyzed by intraclass correlation coefficients (ICC) with 95% confidence intervals and Bland-Altman plots. Bias and the 95% limits of agreement were also calculated.

RESULTS

The safety and feasibility arm of the study demonstrated high degree of safety and tolerability and reliable acquisition of tactile signals. In the reproducibility arm, 10 pregnant women were recruited at mean gestational age of 34.2 ± 6.5 weeks. The mean perineum elasticity (Young's modulus, E) was 9.8 ± 5.9 kPa, and the mean pubic bone-perineal critical distance (D) at 20 kPa load was 34.6 ± 6.2 mm. The ICC was 0.97 [95% confidence interval (CI) 0.91, 0.99] and 0.82 [CI 0.44, 0.95] for E and D respectively, consistent with excellent intrarater agreement. The bias and the 95% limits of agreement of E were -6.3% and -29.4% to +16.7%, respectively. The bias and the 95% limits of agreement of D were -2.6% and -25.3% to +20.2%, respectively.

CONCLUSIONS

The tactile imaging data obtained in the study reproducibly characterized perineal elasticity and pubic bone-perineal critical distance. Further evaluation of this tool in clinical settings is warranted.

Cervical Characterization with Tactile-Ultrasound Probe

BACKGROUND

Premature cervical softening and shortening may be considered an early mechanical failure that predisposes to preterm birth. Preliminary clinical studies demonstrate that cervical elastography may be able to quantify this phenomenon and predict spontaneous preterm delivery.

OBJECTIVE

To explore a new approach for cervix elasticity and length measurements with tactile-ultrasound probe.

METHODS

Cervix probe has tactile array and ultrasound transducer designed to apply controllable load to cervix and acquire stress-strain data for calculation of cervical elasticity (Young's modulus) and cervical length for four cervix sectors. Average values, standard deviations, intraclass correlation coefficients and the 95% limits of agreement (Bland-Altman plots) were estimated.

RESULTS

Ten non-pregnant and ten pregnant women were examined with the probe. The study with non-pregnant women demonstrated a reliable acquisition of the tactile signals. The ultrasound signals had a prolonged appearance; identification of the internal os of the cervix in these signals was not reliable. The study with pregnant women with the gestational age of 25.4 ± 2.3 weeks demonstrated reliable data acquisition with real-time visualization of the ultrasound signals. Average values for cervical elasticity and standard deviations of 19.7 ± 15.4 kPa and length of 30.7 ± 6.6 mm were calculated based on two measurements per 4 sectors. Measurement repeatability calculated as intraclass correlation coefficients between two measurements at the same cervix sector on pregnant women was found to be 0.97 for cervical elasticity and 0.93 for the cervical length. The 95% limits of agreement of 1) cervical elasticity were from -22.4% to +14.9%, and 2) cervical length from -13.3% to +16.5%.

CONCLUSIONS

This study demonstrated clinically acceptable measurement performance and reproducibility. The availability of stress-strain data allowed the computation of cervical elasticity and length. This approach has the potential to provide cervical markers to predict spontaneous preterm delivery.

Engineering approaches for characterizing soft tissue mechanical properties: A review

From cancer diagnosis to detailed characterization of arterial wall biomechanics, the elastic property of tissues is widely studied as an early sign of disease onset. The fibrous structural features of tissues are a direct measure of its health and functionality. Alterations in the structural features of tissues are often manifested as local stiffening and are early signs for diagnosing a disease. These elastic properties are measured ex vivo in conventional mechanical testing regimes, however, the heterogeneous microstructure of tissues can be accurately resolved over relatively smaller length scales with enhanced spatial resolution using techniques such as micro-indentation, microelectromechanical (MEMS) based cantilever sensors and optical catheters which also facilitate in vivo assessment of mechanical properties. In this review, we describe several probing strategies (qualitative and quantitative) based on the spatial scale of mechanical assessment and also discuss the potential use of machine learning techniques to compute the mechanical properties of soft tissues. This work details state of the art advancement in probing strategies, associated challenges toward quantitative characterization of tissue biomechanics both from an engineering and clinical standpoint.

Biomechanical Mapping of the Female Pelvic Floor: Uterine Prolapse Versus Normal Conditions

INTRODUCTION

Quantitative biomechanical characterization of pelvic supportive structures and functions in vivo is thought to provide insight into the pathophysiology of pelvic organ prolapse (POP). Vaginal tactile imaging is an innovative approach to the biomechanical mapping of the female pelvic floor to quantify tissue elasticity, pelvic support, and pelvic muscle functions. The Vaginal Tactile Imager (VTI) records high definition pressure patterns through the vaginal walls under an applied tissue deformation and during pelvic floor muscle contractions.

OBJECTIVE

The objective of this study is to explore an extended set of 52 biomechanical parameters of the female pelvis for the differentiation and characterization of uterine prolapse relative to normal pelvic floor conditions.

METHODS

Sixty subjects were included in the data analysis from observational and case-controlled studies. Out of these 60, forty-two subjects had normal pelvic floor conditions and 18 subjects had uterine prolapse (no anterior, no posterior prolapse). The VTI, model 2S, was used with an analytical software package to automatically calculate 52 biomechanical parameters for 8 VTI test procedures (probe insertion, elevation, rotation, Valsalva maneuver, voluntary muscle contractions in 2 planes, relaxation, and reflex contraction).

RESULTS

The ranges, mean values, and standard deviations for all 52 VTI parameters were established. Twenty-two of 52 parameters were identified as statistically sensitive (p < 0.05; t-test) to the development of uterine prolapse. Among these 21 parameters, 6 parameters show changes (decrease) in tissue elasticity, 5 parameters show deteriorations in pelvic support, and 10 parameters show weakness in muscle functions for uterine prolapsed versus normal conditions.

CONCLUSION

The biomechanical mapping of the female pelvic floor with the VTI provides a unique set of parameters characterizing uterine prolapse versus normal conditions. These objectively measurable biomechanical transformations of pelvic tissues, support structures, and functions under the prolapse conditions may be useful in future research and practical applications.