Force-length relationship in the pelvic floor muscles under transverse vaginal distension: a method study in healthy women

Accuracy and Reliability of Different Approaches for the Assessment of Pelvic Floor Muscle Strength: A Systematic Review

There had been various methods employed for the evaluation of pelvic floor muscle (PFM) strength. The aim of the study was to do a systemic review of these methods for a better understanding of these techniques and to find the best appropriate method. A systemic review of the literature was done using three databases that included: PubMed, Scopus and Web of Science using the keywords "pelvic floor anatomy" and "functional anatomy of pelvic floor muscles" from 1985 to 2022. All the studies involved were analyzed for the methodologies used by the researcher, advantages, disadvantages, and the conclusion of the study. A total of 1,876 studies were found, out of which only 64 met the criteria of inclusion. In these studies, seven methods were used for the determination of PFM strength. These methods included: clinical palpation, perineometer, electromyography, dynamometer, ultrasonography, magnetic resonance imaging, and vaginal cones. The PFM cannot be calculated accurately using any one measuring technique. There is therefore no "gold standard" approach to PFM assessment. However, combining these methods will result in the best outcomes. According to the literature review, the most often employed procedures were digital palpation, perineometry, and Ultrasonography (USG).

The state of pelvic floor muscle dynamometry: A scoping review

AIMS

To discuss the advantages and limitation of the different pelvic floor muscle (PFM) dynamometers available, both in research and industry, and to present the extent of variation between them in terms of structure, functioning, psychometric properties, and assessment procedures.

METHODS

We identified relevant studies from four databases (MEDLINE, Compendex, Web of Science, and Derwent Innovations Index) up to December 2020 using terms related to dynamometry and PFM. In addition, we conducted a hand search of the bibliographies of all relevant reports. Peer-reviewed papers, conference proceedings, patents and user's manuals for commercial dynamometers were included and assessed by two independent reviewers.

RESULTS

One hundred and one records were included and 23 PFM dynamometers from 15 research groups were identified. From these, 20 were considered as clinical dynamometers (meant for research settings) and three as personal dynamometers (developed by the industry). Overall, significant heterogeneity was found in their structure and functioning, which limits development of normative data for PFM force in women. Further research is needed to assess the psychometric properties of PFM dynamometers and to standardize assessment procedures.

CONCLUSION

This review points up to the heterogeneity of existing dynamometers and methods of assessing PFM function. It highlights the need to better document their design and assessment protocol methods. Additionally, this review recommends standards for new dynamometers to allow the establishment of normalized data.

Portable Dynamometer-Based Measurement of Pelvic Floor Muscle Force

OBJECTIVE

In attempts to improve the quality of life of women, continuous projects are sought between rehabilitation intervention and engineering. Using the knowledge of the pelvic floor muscle (PFM) physiology, assessment and training methods are developed to reduce lower urinary tract symptoms such as urinary incontinence. Therefore, this paper covers the design and implementation of a portable vaginal dynamometer.

METHODS

A PFM probe is designed, 3D printed, assembled, and tested in ten women to assess its acceptability and usability. The feedback from the usability study is used to optimize the PFM probe design. A vaginal dynamometer is developed based on the designed PFM probe, then tested for linearity, repeatability, hysteresis, noise and heat effect, and power consumption. The variability between the different produced PFM probe prototypes is evaluated.

RESULTS

Force measurements are made using a load cell. Wireless communication is performed through a Bluetooth low energy transceiver v5.0, with a corresponding interface on both computer and smartphone. The device operates at a 3.3V supply and achieves a power consumption of 49.5 mW in operating mode. Two PFM probe sizes are designed to accommodate different vaginal hiatus sizes, based on usability study feedback. The proposed system allows the physiotherapist to wirelessly monitor variation in pelvic floor muscle force during assessment and/or training.

DISCUSSION/CONCLUSION

The testing results showed that the newly designed system has the potential to measure the PFM function in functional conditions such as the standing position.

External Anal Sphincter Fatigability: An Electromyographic and Manometric Study in Patients With Anorectal Disorders

Background/Aims

External anal sphincter (EAS) plays an important role in fecal and gas voluntary continence. Like every muscle, it can be affected by repeated efforts due to fatigability (physiological response) and/or fatigue (pathological response). No standardized fatiguing protocol and measure method to assess EAS fatigability has existed. The aim is to test a simple, standardized protocol for fatiguing and measuring EAS fatigability and fatigue to understand better the part of EAS fatigability in the pathophysiology of fecal incontinence.

Methods

Patients with anorectal disorders evaluated with anorectal manometry were included. They had to perform 10 repetitions of maximum voluntary contraction (MVC) of 20 seconds. Measurement was made with an anorectal manometry catheter and a surface recording electromyography (EMG). The primary outcome was the difference in EMG root mean square between the first and the last MVC. Secondary outcomes were differences in other EMG and manometry parameters between the first and the last MVC. Difficulties and adverse effects were recorded.

Results

Nineteen patients underwent the fatiguing protocol. All patients completed the entire protocol and no complications were found. No difficulty was declared by the examiner. A significant decrease in root mean square was found between the first and last MVC (0.01020 ± 0.00834 mV vs 0.00661 ± 0.00587 mV; P = 0.002), in maximum anal pressure area under the curve of continuous recordings of anal pressure and mean and total EMG power (P < 0.05).

Conclusions

This protocol is simple and minimally invasive to measure EAS fatigue and fatigability. We highlighted a fatigue of EAS in many patients with anorectal disorders.

Design and validation of an automated dual-arm instrumented intravaginal dynamometer

AIMS

(1) To present the design of a novel intravaginal dynamometer (IVD) capable of measuring vaginal closure force on both the anterior and posterior arms, (2) to use bench testing to validate the force, speed of arm opening, and positional accuracy of load measurement along the IVD arms, and (3) to present in vivo force measurements made with this device, comparing forces measured by the anterior and posterior arms.

METHODS

IVD load measurements were validated against an Instron® Universal Tester, arm opening speeds were validated using video analysis, and position-load accuracy was validated against calibration weights. In vivo IVD data were acquired from female volunteers during passive opening and pelvic floor muscle contraction tasks. Anterior and posterior IVD arm force outcomes were compared.

RESULTS

Forces measured by the IVD and Instron® exhibited a strong linear relationship with excellent model fit. The speed control system was valid when tested under physiological loading conditions, however smaller antero-posterior opening diameters (25 and 30 mm) exhibited some error. The loading position along the IVD arms had no effect on force outcomes. In vivo data exhibited differences between force outcomes measured at the anterior and posterior aspects of the vagina during active contraction and passive elongation of the pelvic floor muscles.

CONCLUSIONS

This IVD design demonstrates valid load measurement and speed control during bench testing. Active and passive forces measured are consistent with the literature. With dual instrumented arms, this device allows for further investigation into the source of measured vaginal closure forces.

Pelvic floor muscle function and symptoms of dysfunctions in midwifes and nurses of reproductive age with and without pelvic floor dysfunction

OBJECTIVES

This study aims to compare pelvic floor muscle (PFM) functions in midwifes and nurses of reproductive age with and without pelvic floor dysfunction (PFD) and investigate the relationship between PFM function and the number, type and symptoms of PFDs.

MATERIALS AND METHODS

82 midwifes and nurses of reproductive age with (n = 51) and without PFD (n = 31) participated in the study. PFM function was assessed by digital palpation using PERFECT scale. Gynecological examination, ultrasonography, disease-specific questionnaires, questions and tests were used to assess symptoms of PFD. PFD was assessed in terms of risk factors, urinary incontinence, fecal incontinence, pelvic organ prolapse (POP), pelvic pain and sexual dysfunctions.

RESULTS

Power parameter of PERFECT scheme was significantly lower in subjects with PFD compared to Non-PFD group (p = 0.002). 41% of the subjects with Power 5 PFM strength in PFD group were diagnosed as stage 1 POP, 5.8% as stage 2 POP, 15.7% of urge incontinence, 23.3% of stress incontinence and 10.5% of mixed incontinence. Both urinary incontinence and POP were detected in 15.7% of them. Among all subjects, incontinence symptoms decreased whereas POP and sexual function did not change as PFM increased. PFM strength was negatively correlated with the number of PFD (p = 0.002, r = -0.34). The type of dysfunction did not correlate with PFM strength (p > 0.05).

CONCLUSION

PFM strength only affects of urinary incontinence sypmtoms among all PFDs in midwifes and nurses of reproductive age. PFM strength may not be the main factor in the occurrence of PFDs as pelvic floor does not consist solely of muscle structure. However, it strongly affects the number of dysfunctions. Therefore, PFM training should be performed to prevent the occurrence of extra dysfunctions in addition to the existing ones even if it does not alter the symptoms.

An automated intravaginal dynamometer: Reliability metrics and the impact of testing protocol on active and passive forces measured from the pelvic floor muscles

AIMS

(1) To determine the reliability of an automated dynamometer designed to assess pelvic floor muscle (PFM) strength and resistance to passive elongation. (2) To evaluate the impact of PFM length and rate of tissue elongation on dynamometric outcomes.

METHODS

At each of two sessions, twenty nulliparous women performed three maximum voluntary contractions (MVC) of their PFMs with the dynamometer set to two different anteroposterior (AP) diameters (25 mm, 35 mm). Next, with PFMs relaxed, the arms of the dynamometer opened three times to 40 mm at two speeds (25 mm/s, 50 mm/s). Outcomes included baseline force, peak force, relative peak force, rate of force development (RFD), stiffness and stress relaxation. Repeated-measures ANOVAs were used to test trial, day, and task effects (α = 0.05), and intra-class correlation coefficients (ICCs) were computed.

RESULTS

Forces measured on MVC were higher with the larger AP diameter, and passive resistance was higher for the faster rate of tissue elongation. The between-trial reliability of all outcomes was excellent (0.82 < ICC < 0.98) for all measures except for peak force during the passive elongation task (0.56 < ICC < 0.93). Between-day reliability was good to excellent for active and passive RFD (0.75 < ICC < 0.93), stiffness (ICC = 0.77) and relative peak force (0.71 < ICC < 0.87); absolute force (0.11 < ICC < 0.85) and stress relaxation responses (0.19 < ICC < 0.98) tended to be less reliable.

CONCLUSIONS

The reliability of the dynamometer is adequate for both clinical and research applications. Relative forces were more reliable than absolute forces. Dimensions and rate of tissue elongation should be controlled and reported with all pelvic floor muscle assessments as these parameters impact outcomes.

Active and Passive Components of Pelvic Floor Muscle Tone in Women with Provoked Vestibulodynia: A Perspective Based on a Review of the Literature

AIM

Pelvic floor muscle (PFM) dysfunctions, especially elevated tone or tension, are suggested to play an important role in the pathophysiology of provoked vestibulodynia (PVD). However, the involvement of the PFMs remains misunderstood as the assessment of muscle tone is complex and requires a thorough understanding of muscle physiology in relation to the characteristics and limitations of current PFM assessment tools. The aim of this review was to describe the structures and mechanisms involved in muscle tone in normally innervated muscle, and to discuss and relate these concepts to the PFM findings in women with PVD.

METHODS

A narrative overview of the literature retrieved from searches of electronic databases and hand searches.

RESULTS

Muscle tone in a normally innervated muscle comprises both active (contractile) and passive (viscoelastic) components. Current methods for evaluating PFM tone such as digital palpation, ultrasound imaging, pressure perineometry, dynamometry, and electromyography may evaluate different components. Research findings suggestive of PFM hypertonicity in women with PVD include elevated general PFM tone, changes in viscoelastic properties, and at least in some women, abnormal increases in electrogenic activity.

CONCLUSION

There is a growing body of evidence to support the involvement of PFM hypertonicity in the pathophysiology of PVD. Limitations of the instruments as well as their properties should be considered when evaluating PFM tone in order to obtain better insight into which component of PFM tone is assessed. Future research is required for further investigating the underlying mechanisms of PFM hypertonicity, and studying the specific effects of physiotherapeutic interventions on PFM tone in women with PVD.

Intra and inter-rater reliability study of pelvic floor muscle dynamometric measurements

OBJECTIVE:

The aim of this study was to evaluate the intra and inter-rater reliability of pelvic floor muscle (PFM) dynamometric measurements for maximum and average strengths, as well as endurance.

METHOD:

A convenience sample of 18 nulliparous women, without any urogynecological complaints, aged between 19 and 31 (mean age of 25.4±3.9) participated in this study. They were evaluated using a pelvic floor dynamometer based on load cell technology. The dynamometric evaluations were repeated in three successive sessions: two on the same day with a rest period of 30 minutes between them, and the third on the following day. All participants were evaluated twice in each session; first by examiner 1 followed by examiner 2. The vaginal dynamometry data were analyzed using three parameters: maximum strength, average strength, and endurance. The Intraclass Correlation Coefficient (ICC) was applied to estimate the PFM dynamometric measurement reliability, considering a good level as being above 0.75.

RESULTS:

The intra and inter-raters' analyses showed good reliability for maximum strength (ICC_intra-rater1=0.96, ICC_intra-rater2=0.95, and ICC_inter-rater=0.96), average strength (ICC_intra-rater1=0.96, ICC_intra-rater2=0.94, and ICC_inter-rater=0.97), and endurance (ICC_intra-rater1=0.88, ICC_intra-rater2=0.86, and ICC_inter-rater=0.92) dynamometric measurements.

CONCLUSIONS:

The PFM dynamometric measurements showed good intra- and inter-rater reliability for maximum strength, average strength and endurance, which demonstrates that this is a reliable device that can be used in clinical practice.

Anal sphincter complex muscles defects and dysfunction in asymptomatic parous women

INTRODUCTION AND HYPOTHESIS

We aimed to determine anatomy and function of anal sphincter complex using three-dimensional ultrasound (3D-US) and manometry in asymptomatic parous women.

METHODS

3D-US of puborectalis muscle (PRM), external (EAS), and internal anal sphincters (IAS) anatomy was performed in 45 women without pelvic floor dysfunction. To assess function, rest and squeeze vaginal and anal pressures were measured. Based on 3D-US, subjects were divided into injured and uninjured groups.

RESULTS

Forty-four of 45 subjects had adequate PRM images. The injured PRM (N = 14) group had significantly lower vaginal pressures as compared with uninjured PRM group (N = 30; p = 0.001). Four of 45 subjects with IAS and EAS defects had lower resting and squeeze anal canal pressure. Muscle injury to IAS, EAS and PRM in the same individual was uncommon.

CONCLUSIONS

In asymptomatic parous women, PRM defects were more common than the EAS/IAS defects but defects in more than one muscle were infrequent. Subjects with injured PRM had low vaginal pressure than the ones without.

Dynamic assessment of the vaginal high-pressure zone using high-definition manometery, 3-dimensional ultrasound, and magnetic resonance imaging of the pelvic floor muscles

OBJECTIVE

We used a novel technique, high-definition manometry (HDM) that utilizes 256 tactile sensitive microtransducers to define the characteristics of vaginal high-pressure zone.

STUDY DESIGN

Sixteen nullipara asymptomatic women were studied using HDM, transperineal 2-dimensional dynamic ultrasound and dynamic magnetic resonance (MR) imaging.

RESULTS

Vaginal high-pressure zone revealed higher contact pressures in anterior and posterior directions compared with lateral directions, both at rest and squeeze. At rest, anterior pressure cluster is located 10 mm cephalad to posterior pressure cluster; with squeeze the latter moves in the cranial direction by 7 mm. Ultrasound and MR images revealed that the anorectal angle moves cephalad and ventrally during squeeze. Cephalad movement of posterior pressure cluster during squeeze is similar to the cranial movement of anorectal angle.

CONCLUSION

We propose that the vaginal high-pressure zone represents the constrictor function and cranial movement of the posterior pressure cluster represents the elevator function of pelvic floor. HDM may be used to measure the constrictor and elevator functions of pelvic floor muscles.

Evidence for benefit of transversus abdominis training alone or in combination with pelvic floor muscle training to treat female urinary incontinence: A systematic review

AIMS

Pelvic floor muscle training (PFMT) has Level A evidence to treat female urinary incontinence (UI). Recently, indirect training of the pelvic floor muscles (PFM) via the transversus abdominis muscle (TrA) has been suggested as a new method to treat UI. The aim of this article is to discuss whether there is evidence for a synergistic co-contraction between TrA and PFM in women with UI, whether TrA contraction is as effective, or more effective than PFMT in treating UI and whether there is evidence to recommend TrA training as an intervention strategy.

METHODS

A computerized search on PubMed, and hand searching in proceedings from the meetings of the World Confederation of Physical Therapy (1993-2007), International Continence Society and International Urogynecology Association (1990-2007) were performed.

RESULTS

While a co-contraction of the TrA normally occurs with PFM contraction, there is evidence that a co-contraction of the PFM with TrA contraction can be lost or altered in women with UI. No randomized controlled trials (RCTs) were found comparing TrA training with untreated controls or sham. Two RCTs have shown no additional effect of adding TrA training to PFMT in the treatment of UI.

CONCLUSIONS

To date there is insufficient evidence for the use of TrA training instead of or in addition to PFMT for women with UI. Neurourol. Urodyn. 28:368-373, 2009. (c) 2009 Wiley-Liss, Inc.

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.

Force and stiffness of the pelvic floor as function of muscle length: A comparison between women with and without stress urinary incontinence

AIMS

To compare passive and active mechanical properties in the pelvic floor as a function of tissue length in continent and incontinent parous women.

MATERIALS AND METHODS

Twenty-four parous continent and 21 parous incontinent women were examined with an intravaginal device. Passive and active force/stiffness were measured by increasing the transverse diameter of the vagina. To allow a more accurate comparison between groups, measured forces were normalized with respect to bodyweight, that is, force/bodyweight.

RESULTS

In both groups passive and active forces increased as a function of the increase in length of the pelvic floor tissues. No difference was found between the groups according to passive forces (P = 0.646), but active force was significantly higher (P = 0.030) in the continent group when normalized for bodyweight. There was an almost linear increase in normalized passive stiffness in the range tested. No differences were found between the groups (P = 0.855). Normalized active stiffness was significantly reduced in the incontinent group (P = 0.021).

CONCLUSIONS

This study indicates that both active force development and active stiffness in the pelvic floor tissues are significantly reduced in incontinent women, whereas the passive resting mechanical forces in the pelvic floor tissues in both groups are not different.