Length tension function of puborectalis muscle: implications for the treatment of fecal incontinence and pelvic floor disorders

Current and future perspectives on the utility of provocative tests of anal sphincter function: A state-of-the-art summary

BACKGROUND

The maintenance of fecal continence depends upon coordinated interactions between the pelvic floor, anorectum, and anal sphincter complex orchestrated by central and peripheral neural activities. The current techniques to objectively measure anorectal function rely on fixed diameter catheters placed inside the anal canal with a rectal balloon to obtain measurements of anal resting and squeeze function, and rectal compliance. Until recently it had not been possible to measure the distensibility of the anal canal, or in other words its ability to resist opening against an increasing pressure, which has been proposed as the main determinant of a biological sphincter's function. Anal acoustic reflectometry (AAR) and the functional lumen imaging probe (FLIP) are two novel, provocative techniques that dynamically assess the anal sphincter complex under volume-controlled distension. In doing so, both provide information on the viscoelastic properties of the anal canal and offer new insights into its function.

PURPOSE

This review details the current and potential future applications of AAR and FLIP and highlights the unanswered questions relevant to these new technologies.

Risk factors of pelvic floor muscle strength in south Chinese women: a retrospective study

Objectives

To evaluate pelvic floor muscle strength using surface electromyography and risk factors for pelvic floor muscle strength in the early postpartum period.

Methods

This retrospective study included 21,302 participants who visited Fujian Maternity and Child Health Hospital from September 2019 to February 2022. All participants were assessed by medical professionals for general information and surface electromyography.

Results

Univariate analysis indicated that age was inversely related to tonic and endurance contractions. In contrast, all the other variables, including education level, body mass index, neonatal weight, and number of fetuses, had a positive impact on rapid, tonic, and endurance contractions. Likewise, parity was also positively associated with rapid contractions. In addition, compared with vaginal delivery, cesarean section delivery had a protective effect on the amplitude of the three types of contractions. Stepwise regression analysis showed that both age and neonatal weight had a negative linear relationship with the amplitude of rapid, tonic and endurance contractions. In contrast, the amplitude of rapid, tonic and endurance contractions significantly increased as body mass index, parity (≤ 3), education level and gestational weight gain (endurance contractions only) increased. Participants with cesarean section delivery showed positive effects on rapid, tonic, and endurance contractions compared to participants with vaginal delivery.

Conclusions

We found that age, neonatal weight, vaginal delivery, episiotomy, and forceps delivery were risk factors for pelvic floor muscle strength; in contrast, body mass index, parity (≤ 3) and gestational weight gain had a positive relationship with pelvic floor muscle strength.

Anorectal Anatomy and Function

Anatomy of pelvic floor muscles has long been controversial. Novel imaging modalities, such as three-dimensional transperineal ultrasound imaging, MRI, and diffusion tensor imaging, have revealed unique myoarchitecture of the external anal sphincter and puborectalis muscle. High-resolution anal manometry, high-definition anal manometry, and functional luminal imaging probe are important new tools to assess anal sphincter and puborectalis muscle function. Increased understanding of the structure and function of anal sphincter complex/pelvic floor muscle has improved the ability to diagnose patients with pelvic floor disorders. New therapeutic modalities to treat anal/fecal incontinence and other pelvic floor disorders will emerge in the near future.

Comparison of Anorectal Function as Measured with High-Resolution and High-Definition Anorectal Manometry

INTRODUCTION

Anorectal manometry (ARM) provides comprehensive assessment of pressure activity in the rectum and anal canal. Absolute pressure values might depend on the catheter used.

OBJECTIVE

Our aim was to compare the results obtained by different anorectal catheters in children with functional anorectal disorders.

METHODS

Children diagnosed with functional defecation disorders based on the Rome IV criteria were prospectively enrolled. ARM was performed in the supine position successively using 2 different probes in each patient in random order. Resting, squeeze pressures, and bear-down maneuver variables obtained by high-resolution (2-dimensional [2D]) and high-definition (3-dimensional [3D]) catheters were compared.

RESULTS

We prospectively included 100 children {mean age 7.5 [standard deviation (SD) ± 4.3] years; 62 boys}. Mean resting pressures were significantly higher when measured with the 3D than with the 2D catheter (71 [SD ± 19.4] vs. 65 [SD ± 20.1] mm Hg, respectively; p = 0.000). Intrarectal pressure measured by 3D and 2D catheters was similar (35 vs. 39 mm Hg, respectively; p = 0.761), but the percent of anal relaxation appeared to be higher for the 3D than for the 2D probe (12 vs. 5%, respectively; p = 0.002). Dyssynergic defecation (DD) was diagnosed in 41/71 patients (57.7%) using the 3D probe and in 51/71 children (71.8%) using the 2D probe (p = 0.044). Cohen's kappa showed only fair agreement between the catheters (κ = 0.40) in diagnosis of DD.

CONCLUSIONS

Our study demonstrated significantly different values of pressures obtained with different types of catheters. Normal ranges for conventional manometry cannot be applied to high-resolution systems, and results obtained by different types of manometry cannot be compared without adjustments (NCT02812823).

Evaluation of Age- and Radical-Prostatectomy Related Changes in Male Pelvic Floor Anatomy Based on Magnetic Resonance Imaging and 3-Dimensional Reconstruction

Purpose

Puborectalis muscles (PRM) and ischiocavernosus muscles (ICM) play important roles in urinary continence and male erectile functions. Understanding of anatomy and surgical-injury related changes to these muscles is critical to monitor changes in continence or erectile function. Anatomical description of these muscles has undergone revisions because these conclusions were derived from cadavers. Our objectives were to: (i) elucidate male pelvic muscles by in-vivo magnetic resonance imaging (MRI) and 3-dimensional (3-D) reconstruction of these images and (ii) compare PRM and ICM thickness in healthy volunteers and symptomatic patients.

Materials and Methods

Healthy young male (mean age, 25 years; n=5), older male (age, 65–70 years; n=5), and post-prostatectomy patients with erectile dysfunction and urinary incontinence (age, 65–70 years; n=5) were scanned on a 3T-magnetic resonance scanner. Images were acquired from slices above urinary bladder base to urethra entry into penis. Pelvic bone, bladder/urethra, corpus cavernosum, ICM, PRM, and prostate were segmented. 3-D models of each structure were generated and assembled into composite images, and ICM and PRM thicknesses were calculated.

Results

We successfully reconstructed 3-D male pelvic floor anatomy including ICM, PRM, bladder, urethra, bulbospongiosus, corpus cavernosa, prostate and bones from the two groups. We documented significant reduction in PRM and ICM thickness in older men.

Conclusions

This is perhaps the first 3-D reconstruction of male pelvic floor structures based on in-vivo MRI in healthy and symptomatic patients. Observed reduction in PRM and ICM thickness is possibly due to age-related atrophy.

Endoflip vs high-definition manometry in the assessment of fecal incontinence: A data-driven unsupervised comparison

BACKGROUND

How much anal sphincter dysfunction contributes to fecal incontinence (FI) is not clear. High-definition anorectal manometry (HDAM) and functional luminal imaging probe (Endoflip) are two new techniques to study anal sphincter function.

AIMS

The goal was to compare the diagnostic utility of HDAM and Endoflip using optimal feature(s) in each modality for FI diagnosis.

METHODS

Blinded classification was carried out on 70 female subjects (32 FI & 38 controls), using 3 prominent machine-learning clustering techniques, with 3 distance metrics. For HDAM, descriptive statistics, shape, and textural features characterizing the spatial relationship of pixels in the HDAM high-pressure zone, and for Endoflip, permutations of pressure and CSA combinations (ie, multiplication, division, or individually) at rest and squeeze were tested.

RESULTS

Intramodality: (a) Endoflip: Best clustering was obtained using the combination of the ratio of CSA over pressure at 40 and 50 mL at rest, which had significantly better specificity (P < 0.001) than using only pressure at 50 mL, no difference in sensitivity (P = 0.68). (b) HDAM: clustering using textural information at rest had significantly higher specificity compared to using only the maximal pressure at rest (P < 0.001). Intermodality: Clustering results using optimal features were not significantly different with respect to sensitivity or specificity (P > 0.05). Optimal Endoflip feature set differed significantly in specificity compared to HDAM maximal pressure at both rest (P < 0.001) and squeeze (P < 0.001).

CONCLUSION

Defective anal closure function is fairly sensitive and highly specific in diagnosing FI. Using optimal feature sets, HDAM and Endoflip perform in a similar fashion in diagnosing FI, but are not complementary.

Measuring length-tension function of the anal sphincters and puborectalis muscle using the functional luminal imaging probe

The functional luminal imaging probe (FLIP) has been used to measure the distensibility of the anal canal. We hypothesized that with increasing distension of the anal canal with FLIP there will be an increase in length of the anal sphincter muscle allowing measurement of the length-tension function of anal sphincter and puborectalis muscles (PRM). We studied 14 healthy nulliparous women. A custom-designed FLIP bag (30-mm diameter) was placed in the vagina and then in the anal canal, distended in 10-ml steps with volumes ranging from 30 to 90 ml. At each volume, subject performed maximal voluntary squeezes. Length-tension measurements were also made with a manometric probe system. Tension was calculated (pressure × radius) in Newtons per meter using a custom software program. Peak tensions at different FLIP volumes were compared with the manometric data. No change in the luminal CSA was noted at low fluid volumes; the sphincter muscles were able to fully collapse the FLIP bag within the anal canal/vagina even at rest. At larger volumes, with each squeeze there was an increase in the bag pressure and reduction in the cross-sectional area, which represents concentric contraction of the muscle. Both rest and squeeze tension increased with the increase in volume in the anal as well as vaginal canal indicating that the external anal sphincter and puborectalis muscles produce more tension when lengthened. FLIP device, which has been used to describe the distensibility of the anal canal can also provide information on the length-tension function of the anal sphincters and PRM. NEW & NOTEWORTHY The functional luminal imaging probe (FLIP) has been used to describe the distensibility of the anal canal. This report is the first to describe the use of the FLIP in the vaginal canal and the anal canal to provide information on the length-tension function of the anal sphincter and puborectalis muscles, which may provide clinicians with additional information regarding the active components of muscle contraction involved in the anal closure function.

Anatomy and mechanical properties of the anal sphincter muscles in healthy senior volunteers

BACKGROUND

A large proportion of age-related fecal incontinence is attributed to weakness or degeneration of the muscles composing the anal continence organ. However, the individual role of these muscles and their functional interplay remain poorly understood.

METHODS

This study employs a novel technique based on the combination of MR imaging and FLIP measurements (MR-FLIP) to obtain anatomical and mechanical information simultaneously. Unlike previous methods used to assess the mechanics of the continence organ, MR-FLIP allows inter-individual comparisons and statistical analysis of the sphincter morpho-mechanical parameters. The anatomy as well as voluntary and involuntary mechanical properties of the anal continence organ were characterized in 20 healthy senior volunteers.

RESULTS

Results showed that the external anal sphincter (EAS) forms a funnel-like shape with wall thickness increasing by a factor of 2.5 from distal (6 ± 0 mm) to proximal (15 ± 3 mm). Both voluntary and involuntary mechanical properties in this region correlate strongly with the thickness of the muscle. The positions of least compliance and maximal orifice closing were both located toward the proximal EAS end. In addition, maximal contraction during squeeze maneuvers was reached after 2 s, but high muscle fatigue was measured during a 7 s holding phase, corresponding to about 60% loss of the energy produced by the muscles during the contraction phase.

CONCLUSIONS

This work reports baseline parameters describing the morpho-mechanical condition of the sphincter muscle of healthy elderly volunteers. New parameters were also proposed to quantify the active properties of the muscles based on the mechanical energy associated with muscle contraction and fatigue. This information could be used to assess patients suffering from AI or for the design of novel implants.

Thermosensitive hydrogels a versatile concept adapted to vaginal drug delivery

Vaginal drug delivery represents an attractive strategy for local and systemic delivery of drugs otherwise poorly absorbed after oral administration. The rather dense vascular network, mucus permeability and the physiological phenomenon of the uterine first-pass effect can all be exploited for therapeutic benefit. However, several physiological factors such as an acidic pH, constant secretion, and turnover of mucus as well as varying thickness of the vaginal epithelium can impact sustained drug delivery. In recent years, polymers have been designed to tackle challenges mentioned above. In particular, thermosensitive hydrogels hold great promise due to their stability, biocompatibility, adhesion properties and adjustable drug release kinetics. Here, we discuss the physiological and anatomical uniqueness of the vaginal environment and how it impacts the safe and efficient vaginal delivery and also reviewed several thermosensitive hydrogels deemed suitable for vaginal drug delivery by addressing specific characteristics, which are essential to engage the vaginal environment successfully.