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

Comparison of the Vaginal and Labial Dimensions of Ethnic Chinese and Western Nullipara

INTRODUCTION AND HYPOTHESIS

Vaginal dimensions have clinical and surgical implications. We sought to quantify the differences between vaginal and labial dimensions in healthy ethnic Chinese and Western women with normal pelvic organ support.

METHODS

This is a cross-sectional study of a convenience sample of ethnic Chinese nulliparas (n = 33) and Western nulliparas (n = 33) recruited for research purposes. For each subject, magnetic resonance imaging was used to quantify the vaginal and labial dimensions. Specifically, we identified the anterior and posterior vaginal wall, the outline of the cervix in the mid-sagittal and coronal planes, and the distance from the labia majora to the hymenal ring at the urethral meatus.

RESULTS

There were significant differences in age and weight between groups. Substantial variation in vaginal and labial dimensions was found within each group. The vaginal and labial dimensions of ethnic Chinese women ranged from 9-21% smaller than those of Western women; In the ethnic Chinese group, increasing weight and BMI correlated with greater labial distance (r = 0.66 and r = 0.63 respectively); as did height and the distance from the vaginal opening to the cervical os (r = 0.5). In the Western group, only weight correlated with the labial distance (r = 0.51).

CONCLUSIONS

Significant group differences in vaginal and labial dimensions were found, with the dimensions of Chinese nulliparas being up to 21% smaller than those of Western nulliparas.

Analysis of minimal levator ani hiatus area based on MRI in female adults without pelvic floor dysfunction at different age groups

PURPOSE

To investigate the association of minimal levator ani hiatus area with age in female adults without pelvic floor dysfunction.

METHODS

532 female subjects aged 18 ~ 90 years without pelvic floor dysfunction, divided into four groups (Group A, 18 ~ 29 years old; Group B, 30 ~ 39 years old; Group C, 40 ~ 49 years old; Group D, ≥ 50 years old) based on age, underwent traditional pelvic two-dimensional (2D) T2-weighted imaging (T2WI) axial to the body (AxB) for measuring the minimal levator ani hiatus area. 39 female volunteers were re-recruited to undergo both traditional pelvic 2D T2WI AxB and three-dimensional (3D) T2WI. An axial plane parallel to the direction of the puborectalis muscle (AxPRM) was acquired based on 3D T2WI. The difference of levator ani hiatus area measured on AxB and AxPRM images in 39 female volunteers was compared by one-sample t test, to verify if minimal levator ani hiatus area can be acquired on the traditional pelvic 2D T2WI AxB images. Spearman analysis evaluated the association of minimal levator ani hiatus area with age and the rank-sum test analyzed the area differences among four age groups.

RESULTS

Female age was positively correlated with minimal levator ani hiatus area (r = 0.23; p < 0.001). The minimal levator ani hiatus areas of 532 subjects were: 15.17 ± 1.77 cm2 in Group A, 15.52 ± 2.21 cm2 in Group B, 16.03 ± 2.16 cm2 in Group C, and 16.40 ± 2.10 cm2 in Group D. ANOVA showed significant statistical differences among four age groups (F = 7.519, p < 0.0001). Significant differences in minimal levator ani hiatus areas were found between Group A and Group C (p = 0.0491), Group A and Group D (p = 0.0007), and Group B and Group D (p < 0.001). There was no statistical difference in minimal levator ani hiatus areas measured on AxB and AxPRM images in 39 female volunteers (p = 0.1000). There were no statistical difference in minimal levator ani hiatus areas between nulliparous and multiparous group for each age group (all p > 0.05).

CONCLUSIONS

Based on a large sample, this study summarized the minimum levator ani hiatus area of female adults without pelvic floor dysfunction in different age groups. We found significant differences among different age groups. In addition, a positive correlation was found between age and the minimum levator ani hiatus area. These findings can provide reference criteria for diagnosing pelvic organ prolapse in female adults of different age groups.

A unified pelvic floor conceptual model for studying morphological changes with prolapse, age, and parity

Several 2-dimensional and 3-dimensional measurements have been used to assess changes in pelvic floor structures and shape. These include assessment of urogenital and levator hiatus dimensions, levator injury grade, levator bowl volume, and levator plate shape. We argue that each assessment reflects underlying changes in an individual aspect of the overall changes in muscle and fascial structures. Vaginal delivery, aging, and interindividual variations in anatomy combine to affect pelvic floor structures and their connections in different ways. To date, there is no unifying conceptual model that permits the evaluation of how these many measures relate to one another or that reflects overall pelvic floor structure and function. Therefore, this study aimed to describe a unified pelvic floor conceptual model to better understand how the aforementioned changes to the pelvic floor structures and their biomechanical interactions affect pelvic organ support with vaginal birth, prolapse, and age. In this model, the pelvic floor is composed of 5 key anatomic structures: the (1) pubovisceral, (2) puborectal, and (3) iliococcygeal muscles with their superficial and inferior fascia; (4) the perineal membrane or body; and (5) the anal sphincter complex. Schematically, these structures are considered to originate from pelvic sidewall structures and meet medially at important connection points that include the anal sphincter complex, perineal body, and anococcygeal raphe. The pubovisceral muscle contributes primarily to urogenital hiatus closure, whereas the puborectal muscle is mainly related to levator hiatus closure, although each muscle contributes to the other. Dorsally and laterally, the iliococcygeal muscle forms a shelflike structure in women with normal support that spans the remaining area between these medial muscles and attachments to the pelvic sidewall. Other features include the levator plate, bowl volume, and anorectal angle. The pelvic floor conceptual model integrates existing observations and points out evident knowledge gaps in how parturition, injury, disease, and aging can contribute to changes associated with pelvic floor function caused by the detachment of one or more important connection points or pubovisceral muscle failure.

Quantifying the Effects of Aging on Morphological and Cellular Properties of Human Female Pelvic Floor Muscles

Age-related pelvic floor muscle (PFM) dysfunction is a critical defect in the progression to pelvic floor disorders (PFDs). Despite dramatic prevalence of PFDs in older women, the underlying pathophysiology of age-related PFM dysfunction remains poorly understood. Using cadaveric specimens, we quantified aging effects on functionally relevant PFM properties and compared PFMs with the appendicular muscles from the same donors. PFMs, obturator internus, and vastus lateralis were procured from younger (N = 4) and older (N = 11) donors with known obstetrical and medical history. Our findings demonstrate that PFMs undergo degenerative, rather than atrophic, alterations. Importantly, age-related fibrotic degeneration disproportionally impacts PFMs compared to the appendicular muscles. We identified intramuscular lipid accumulation as another contributing factor to the pathological alterations of PFMs with aging. We observed a fourfold decrease in muscle stem cell (MuSC) pool of aged relative to younger PFMs, but the MuSC pool of appendicular muscles from the same older donors was only twofold lower than in younger group, although these differences were not statistically significant. Age-related degeneration appears to disproportionally impact PFMs relative to the appendicular muscles from the same donors. Knowledge of tissue- and cell-level changes in aged PFMs is essential to promote our understanding of the mechanisms governing PFM dysfunction in older women.

Pelvic cross-sectional area at the level of the levator ani and prolapse

INTRODUCTION AND HYPOTHESIS

Intraabdominal pressure acts on the pelvic floor through an aperture surrounded by bony and muscular structures of the pelvis. A small pilot study showed the area of the anterior portion of this plane is larger in pelvic organ prolapse. We hypothesize that there is a relationship between prolapse and anterior (APA) and posterior (PPA) pelvic cross-sectional area in a larger, more diverse population.

STUDY DESIGN

MRIs from 30 prolapse subjects and 66 controls were analyzed in this case-control study. The measurement plane was tilted to approximate the level of the levator ani attachments. Three evaluators made measurements. Patient demographic characteristics were compared using Wilcoxon rank-sum and Fisher's exact tests. A multivariable logistic regression model identified factors independently associated with prolapse.

RESULTS

Controls were 3.7 years younger and had lower parity, but groups were similar in terms of race, height, and BMI. Cases had a larger APA (p < 0.0001), interspinous diameter (ISD) (p = 0.001), anterior-posterior (AP) diameter (p = 0.01), and smaller total obturator internus muscle (OIM) area (p = 0.002). There was no difference in the size of the PPA(p = 0.12). Bivariate logistic regression showed age (p = 0.007), parity (p = 0.009), ISD (p = 0.002), AP diameter (p = 0.02), APA (p < 0.0001), and OIM size (p = 0.01) were significantly associated with prolapse; however, PPA was not (p = 0.12). After adjusting for age, parity, and major levator defect, prolapse was significantly associated with increased anterior pelvic area (p = 0.001).

CONCLUSIONS

We confirm that a larger APA and decreasing OIM area are associated with prolapse. The PPA was not significantly associated with prolapse.

Published Human Cadaveric Measurements Are Strongly Biased Toward the Elderly Population

Understanding of anatomy is based on the study of anatomical variations. Morphometric variations can have important implications in surgical practice. The sizes of some anatomical structures are affected by age; however, cadavers used in anatomical research are usually of advanced age. The main aim of this study is to quantify the mean age of samples in cadaveric studies reporting morphometric values. PubMed was searched for the last 3 years to locate cadaveric studies reporting size values, excluding histological, forensic, and osteological collections. Out of the 390 potentially relevant papers, 109 (28%) studies did not report the ages of their samples. In total, 177 studies were included for analysis comprising 4,807 subjects. The most studied structures were those of the musculoskeletal system. The mean age of the pooled sample was 71.1 ± 11.0 years. The lowest reported age was 16 while the highest was 104 years. Univariate and multivariate analyses showed no correlation with any of the following variables: country of study, anatomical region, anatomical structure, or journal type. The mean age of cadavers used to measure the sizes of human anatomical structures falls largely within the senior age category. The reported values in an aging population will not necessarily mirror other populations such as the pediatric. The outcomes of surgeries that depend to some extent on tight morphometric values such as flap surgeries, microsurgery, tendon transfer, or mini-invasive procedures could differ when they are performed on other age categories. More anatomical research is needed for better reporting of age-related morphometric changes. Clin. Anat., 33:804-808, 2020. © 2019 Wiley Periodicals, Inc.

A novel measurement of pelvic floor cross-sectional area in older and younger women with and without prolapse

BACKGROUND

An increase in size of the aperture of the pelvis that must be spanned by pelvic floor support structures translates to an increase in the force on these structures. Prior studies have measured the bony dimensions of the pelvis, but the effect of changes in muscle bulk that may affect the size of this area are unknown.

OBJECTIVES

To develop a technique to evaluate the aperture size in the anterior pelvis at the level of the levator ani muscle attachments, and to identify age-related changes in women with and without prolapse.

MATERIALS AND METHODS

This was a technique development and pilot case-control study evaluating pelvic magnetic resonance imaging from 30 primiparous women from the Michigan Pelvic Floor Research Group MRI Data Base: 10 younger women with normal support, 10 older women with prolapse, and 10 older menopausal women without prolapse. Anterior pelvic area measurements were made in a plane that included the bilateral ischial spines and the inferior pubic point, approximating the level of the arcus tendineus fascia pelvis. Measurements of the anterior pelvic area, obturator internus muscles, and interspinous diameter were made by 5 independent raters from the Society of Gynecologic Surgeons Pelvic Anatomy Group who focused on developing pelvic imaging techniques, and evaluating interrater reliability. Demographic characteristics were compared across groups of interest using the Wilcoxon rank sum test, χ2, or Fisher exact test where appropriate. Multiple linear regression models were created to identify independent predictors of anterior pelvic area.

RESULTS

Per the study design, groups differed in age and prolapse stage. There were no differences in race, height, body mass index, gravidity, or parity. Patients with prolapse had a significantly longer interspinous diameter, and more major (>50% of the muscle) levator ani defects when compared to both older and younger women without prolapse. Interrater reliability was high for all measurements (intraclass correlation coefficient = 0.96). The anterior pelvic area (cm2) was significantly larger in older women with prolapse compared to older (60 ± 5.1 vs 53 ± 4.9, P = .004) and younger (60 ± 5.1 vs 52 ± 4.6, P = .001) women with normal support. The younger and older women with normal support did not differ in anterior pelvic area (52 ± 4.6 vs 53 ± 4.9, P = .99). After adjusting for race and body mass index, increased anterior pelvic area was significantly associated with the following: being an older woman with prolapse (β = 6.61 cm2, P = .004), and interspinous diameter (β = 4.52 cm2, P = .004).

CONCLUSION

Older women with prolapse had the largest anterior area, suggesting that the anterior pelvic area is a novel measure to consider when evaluating women with prolapse. Interspinous diameter, and being an older woman with prolapse, were associated with a larger anterior pelvic area. This suggests that reduced obturator internus muscle size with age may not be the primary factor in determining anterior pelvic area, but that pelvic dimensions such as interspinous diameter could play a role. The measurements were highly repeatable. The high intraclass correlation coefficient indicates that all raters were able to successfully learn the imaging software and to perform measurements with high reproducibility.

Aging effects on pelvic floor support: a pilot study comparing young versus older nulliparous women

INTRODUCTION AND HYPOTHESIS

We sought to determine age-related changes to the pelvic floor in the absence of childbirth effects.

METHODS

A case-control study was conducted from June 2017 to August 2018 comparing two groups of nulliparous women: <40 years old and ≥ 70 years old. Clinical evaluation included POP-Q, instrumented speculum testing, and handgrip strength. Dynamic 3D-stress MRI was performed on all women to obtain genital and levator hiatus (LH) lengths, LH area, and levator bowl volume. LH shape was quantified using a novel measure called the "V-U index." Pubovisceral muscle (PVM) cross-sectional area (CSA) was also measured. Bivariate comparisons between the two groups were made for all variables. Effect sizes were calculated for MRI measurements.

RESULTS

Twelve young and 9 older nulliparous women were included. Levator bowl volume at rest was 83% larger in older women (108.0 ± 34.5 cm³ vs 59.2 ± 19.3 cm³, p = 0.001, d = 1.82). MRI genital hiatus at rest was larger among the older group (2.7 ± 0.6 cm vs 3.5 ± 0.6 cm, p = 0.007, d = 1.34). V-U index, a measure of LH shape where 0 = "V" and 1 = "U," differed between groups indicating a more "U"-like shape among older women (0.71 ± 0.23 vs 0.35 ± 0.18, p = 0.001, d = 1.72). Handgrip strength was lower in the older vs young group (23.2 ± 5.2 N vs 33.4 ± 5.2 N, p < 0.0001); however, the Kegel augmentation force and PVM CSA were similar (3.2 ± 1.1 N vs 3.3 ± 2.2 N, p = 0.89, and 0.8 ± 0.3 cm² vs 0.7 ± 0.2 cm², p = 0.23 respectively).

CONCLUSIONS

Levator bowl volume at rest was over 80% larger among older women, reflecting a generalized posterior distension with age.

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.

On the variation in maternal birth canal in vivo viscoelastic properties and their effect on the predicted length of active second stage and levator ani tears

The pubovisceral muscles (PVM) help form the distal maternal birth canal. It is not known why 13% of vaginal deliveries end in PVM tears, so insights are needed to better prevent them because their sequelae can lead to pelvic organ prolapse later in life. In this paper we provide the first quantification of the variation in in vivo viscoelastic properties of the intact distal birth canal in healthy nulliparous women using Fung's Quasilinear Viscoelastic Theory and a secondary analysis of data from a clinical trial of constant force birth canal dilation to 8 cm diameter in the first stage of labor in 26 nullipara. We hypothesized that no significant inter-individual variation would be found in the long time constant, τ_2, which characterizes how long it takes the birth canal to be dilated by the fetal head. That hypothesis was rejected because τ₂ values ranged 20-fold above and below the median value. These data were input to a biomechanical model to calculate how such variations affect the predicted length of the active second stage of labor as well as PVM tear risk. The results show there was a 100-fold change in the predicted length of active second stage for the shortest and longest τ₂ values, with a noticeable increase for τ₂ values over 1000 s. The correlation coefficent between predicted and observed second stage durations was 0.51. We conclude that τ₂ is a strong theoretical contributor to the time a mother has to push in order to deliver a fetal head larger than her birth canal, and a weak predictor of PVM tear risk.

A constitutive model description of the in vivo material properties of lower birth canal tissue during the first stage of labor

Remarkable changes must occur in the pelvic floor muscles and tissues comprising the birth canal to allow vaginal delivery. Despite these preparatory adaptations, approximately 13% of women who deliver vaginally for the first time (nulliparas) sustain tears near the origin of the pubovisceral muscle (PVM) which can result in pelvic organ prolapse later in life. To investigate why these tears occur, it is necessary to quantify the viscoelastic behavior of the term pregnant human birth canal. The goal of this study was to quantify the in vivo material properties of the human birth canal, in situ, during the first stage of labor and compare them to published animal data. The results show that pregnant human, ovine and squirrel monkey birth canal tissue can be characterized by the same set of constitutive relations; the interspecies differences were primarily explained by the long time constant, τ₂, with its values of 555s, 1110s, and 2777s, respectively. Quantification of these viscoelastic properties should allow for improved accuracy of computer models aimed at understanding birth-related injuries.

Increasing Age Is a Risk Factor for Decreased Postpartum Pelvic Floor Strength

OBJECTIVES

This study aimed to determine factors associated with decreased pelvic floor strength (PFS) after the first vaginal delivery (VD) in a cohort of low-risk women.

METHODS

This is a secondary analysis of a prospective study examining the risk of pelvic floor injury in a cohort of primiparous women. All recruited participants underwent an examination, three-dimensional ultrasound and measurement of PFS in the third trimester and repeated at 4 weeks to 6 months postpartum using a perineometer.

RESULTS

There were 84 women recruited for the study, and 70 completed the postpartum assessment. Average age was 28.4 years (standard deviation, 4.8). There were 46 (66%) subjects with a VD and 24 (34%) with a cesarean delivery who labored. Decreased PFS was observed more frequently in the VD group compared with the cesarean delivery group (68% vs 42%, P = 0.03).In modified Poisson regression models controlling for mode of delivery and time of postpartum assessment, women who were aged 25 to 29 years (risk ratio = 2.80, 95% confidence interval, 1.03-7.57) and 30 years and older (risk ratio = 2.53, 95% confidence interval, 0.93-6.86) were over 2.5 times more likely to have decreased postpartum PFS compared with women younger than 25 years.

CONCLUSIONS

In this population, women aged 25 years and older were more than twice as likely to have a decrease in postpartum PFS.

Age-related alterations in female obturator internus muscle

INTRODUCTION AND HYPOTHESIS

Pelvic floor muscle rehabilitation is a widely utilized, but often challenging therapy for pelvic floor disorders, which are prevalent in older women. Regimens involving the use of appendicular muscles, such as the obturator internus (OI), have been developed for strengthening of the levator ani muscle (LAM). However, changes that lead to potential dysfunction of these alternative targets in older women are not well known. We hypothesized that aging negatively impacts OI architecture, the main determinant of muscle function, and intramuscular extracellular matrix (ECM), paralleling age-related alterations in LAM.

METHODS

OI and LAM were procured from three groups of female cadaveric donors (five per group): younger (20 - 40 years), middle-aged (41 - 60 years), and older (≥60 years). Architectural predictors of the excursional (fiber length, L _f), force-generating (physiological cross-sectional area, PCSA) and sarcomere length (L _s) capacity of the muscles, and ECM collagen content (measure of fibrosis) were determined using validated methods. The data were analyzed using one-way ANOVA and Tukey's post-hoc test with a significance level of 0.05, and linear regression.

RESULTS

The mean ages of the donors in the three groups were 31.2 ± 2.3 years, 47.6 ± 1.2 years, and 74.6 ± 4.2 years (P < 0.005). The groups did not differ with respect to parity or body mass index (P > 0.5). OI L _f and L _s were not affected by aging. Age >60 years was associated with a substantial decrease in OI PCSA and increased collagen content (P < 0.05). Reductions in OI and LAM force-generating capacities with age were highly correlated (r ² = 0.9).

CONCLUSIONS

Our findings of age-related decreases in predicted OI force production and fibrosis suggest that these alterations should be taken into consideration, when designing pelvic floor fitness programs for older women.

Impact of vaginal parity and aging on the architectural design of pelvic floor muscles

BACKGROUND

Vaginal delivery and aging are key risk factors for pelvic floor muscle dysfunction, which is a critical component of pelvic floor disorders. However, alterations in the pelvic floor muscle intrinsic structure that lead to muscle dysfunction because of childbirth and aging remain elusive.

OBJECTIVES

The purpose of this study was to determine the impact of vaginal deliveries and aging on human cadaveric pelvic floor muscle architecture, which is the strongest predictor of active muscle function.

STUDY DESIGN

Coccygeus, iliococcygeus, and pubovisceralis were obtained from younger donors who were ≤51 years old, vaginally nulliparous (n = 5) and vaginally parous (n = 6) and older donors who were >51 years old, vaginally nulliparous (n = 6) and vaginally parous (n = 6), all of whom had no history of pelvic floor disorders. Architectural parameters, which are predictive of muscle's excursion and force-generating capacity, were determined with the use of validated methods. Intramuscular collagen content was quantified by hydroxyproline assay. Main effects of parity and aging and the interactions were determined with the use of 2-way analysis of variance, with Tukey's post-hoc testing and a significance level of .05.

RESULTS

The mean age of younger and older donors differed by approximately 40 years (P = .001) but was similar between nulliparous and parous donors within each age group (P > .9). The median parity was 2 (range, 1-3) in younger and older vaginally parous groups (P = .7). The main impact of parity was increased fiber length in the more proximal coccygeus (P = .03) and iliococcygeus (P = .04). Aging changes manifested as decreased physiologic cross-sectional area across all pelvic floor muscles (P < .05), which substantially exceeded the age-related decline in muscle mass. The physiologic cross-sectional area was lower in younger vaginally parous, compared with younger vaginally nulliparous, pelvic floor muscles; however, the differences did not reach statistical significance. Pelvic floor muscle collagen content was not altered by parity but increased dramatically with aging (P < .05).

CONCLUSIONS

Increased fiber length in more proximal pelvic floor muscles likely represents an adaptive response to the chronically increased load placed on these muscles by the displaced apical structures, presumably as a consequence of vaginal delivery. In younger specimens, a consistent trend towards decrease in force-generating capacity of all pelvic floor muscles in the parous group suggests a potential mechanism for clinically identified pelvic floor muscle weakness in vaginally parous women. The substantial decrease in predicted muscle force production and fibrosis with aging represent likely mechanisms for the pelvic floor muscle dysfunction in older women.

Variability of the pubic arch architecture and its influence on the minimal levator hiatus area

OBJECTIVE

To investigate the association between the minimal levator hiatus (MLH) area at rest with its surrounding soft-tissue and bony structures in nulliparous asymptomatic women with a normal levator ani muscle.

METHODS

A subanalysis was undertaken of a prospective study of the appearance of the levator ani in asymptomatic nulliparous women conducted between September 2010 and September 2011. The subanalysis included women with a normal levator ani muscle. Three-dimensional ultrasonography volumes were used to obtain pelvic floor measurements.

RESULTS

The analysis included 56 women with mean age of 43.0±13.4years. The mean MLH area was 13.1±1.8cm(2) (range 9.0-17.3). The pubic arch angle had no influence on the MLH area (Pearson correlation coefficient r=0.13). Height and pubic arch length were positively correlated with the MLH area (r=0.26 [P=0.52] and r=0.50 [P<0.001], respectively).

CONCLUSION

The MLH size of nulliparous women varied widely and was positively correlated with the height and pubic arch length of the women. Therefore, caution is warranted when interpreting the MLH area as an indicator of a levator ani defect or a predictor of pelvic organ prolapse without taking a woman's pelvic bone characteristics into account.

Comparison of muscle fiber directions between different levator ani muscle subdivisions: in vivo MRI measurements in women

INTRODUCTION AND HYPOTHESIS

This study describes a technique to quantify muscle fascicle directions in the levator ani (LA) and tests the null hypothesis that the in vivo fascicle directions for each LA subdivision subtend the same parasagittal angle relative to a horizontal reference axis.

METHODS

Visible muscle fascicle direction in the each of the three LA muscle subdivisions, the pubovisceral (PVM; synonymous with pubococcygeal), puborectal (PRM), and iliococcygeal (ICM) muscles, as well as the external anal sphincter (EAS), were measured on 3-T sagittal MRI images in a convenience sample of 14 healthy women in whom muscle fascicles were visible. Mean ± standard deviation (SD) angle values relative to the horizontal were calculated for each muscle subdivision. Repeated measures ANOVA and post-hoc paired t tests were used to compare muscle groups.

RESULTS

Pubovisceral muscle fiber inclination was 41 ± 8.0°, PRM was -19 ± 10.1°, ICM was 33 ± 8.8°, and EAS was -43 ± 6.4°. These fascicle directions were statistically different (p < 0.001). Pairwise comparisons among levator subdivisions showed angle differences of 60° between PVM and PRM, and 52° between ICM and PRM. An 84° difference existed between PVM and EAS. The smallest angle difference between levator divisions was between PVM and ICM 8°. The difference between PRM and EAS was 24°. All pairwise comparisons were significant (p < 0.001).

CONCLUSIONS

The null hypothesis that muscle fascicle inclinations are similar in the three subdivisions of the levator ani and the external anal sphincter was rejected. The largest difference in levator subdivision inclination, 60°, was found between the PVM and PRM.

Comparison of muscle fiber directions between different levator ani muscle subdivisions: in vivo MRI measurements in women

INTRODUCTION AND HYPOTHESIS

This study describes a technique to quantify muscle fascicle directions in the levator ani (LA) and tests the null hypothesis that the in vivo fascicle directions for each LA subdivision subtend the same parasagittal angle relative to a horizontal reference axis.

METHODS

Visible muscle fascicle direction in the each of the three LA muscle subdivisions, the pubovisceral (PVM; synonymous with pubococcygeal), puborectal (PRM), and iliococcygeal (ICM) muscles, as well as the external anal sphincter (EAS), were measured on 3-T sagittal MRI images in a convenience sample of 14 healthy women in whom muscle fascicles were visible. Mean ± standard deviation (SD) angle values relative to the horizontal were calculated for each muscle subdivision. Repeated measures ANOVA and post-hoc paired t tests were used to compare muscle groups.

RESULTS

Pubovisceral muscle fiber inclination was 41 ± 8.0°, PRM was -19 ± 10.1°, ICM was 33 ± 8.8°, and EAS was -43 ± 6.4°. These fascicle directions were statistically different (p < 0.001). Pairwise comparisons among levator subdivisions showed angle differences of 60° between PVM and PRM, and 52° between ICM and PRM. An 84° difference existed between PVM and EAS. The smallest angle difference between levator divisions was between PVM and ICM 8°. The difference between PRM and EAS was 24°. All pairwise comparisons were significant (p < 0.001).

CONCLUSIONS

The null hypothesis that muscle fascicle inclinations are similar in the three subdivisions of the levator ani and the external anal sphincter was rejected. The largest difference in levator subdivision inclination, 60°, was found between the PVM and PRM.

Temporalis muscle morphomics: the psoas of the craniofacial skeleton

BACKGROUND

The psoas muscle has been shown to predict patient outcomes based on the quantification of muscle area using computed tomography (CT) scans. The accuracy of morphomic analysis on other muscles has not been clearly delineated. In this study, we determine the correlation between temporalis muscle mass, psoas muscle area, age, body mass index (BMI), and gender.

METHODS

Temporalis and psoas muscle dimensions were determined on all trauma patients who had both abdominal and maxillofacial CT scans at the University of Michigan between 2004 and 2011. Age, BMI, and gender were obtained through chart review. Univariate and multivariate analyses were performed to determine the relative relationship between morphomic data of the temporalis and psoas muscles and the ability of such information to correspond with clinical variables, such as BMI, age, and gender.

RESULTS

A total of 646 patients were included in the present study. Among the 249 (38.5%) women and 397 (61.5%) men, the average age was 49.2 y. Average BMI was 27.9 kg/m². Total psoas muscle area directly correlated with mean temporalis muscle thickness (r = 0.57, P < 0.001). There was an indirect correlation between age and psoas muscle area (r = -0.52, P < 0.001) and temporalis muscle thickness (r = -0.36, P < 0.001). Neither psoas nor temporalis measurements correlated strongly with BMI (r = 0.18, P < 0.001; r = 0.14, P = 0.002), although stronger correlations were found in a more "frail," subgroup as defined by a BMI of <20 (r = 0.59, P = 0.002).

CONCLUSIONS

We demonstrate that dimensions of the temporalis muscle can be quantified and may serve as a proxy for age. Going forward, we aim to assess the utility of temporalis and psoas morphomics in predicting complication rates among trauma patients admitted to the hospital to predict outcomes in the future.

Architectural design of the pelvic floor is consistent with muscle functional subspecialization

INTRODUCTION AND HYPOTHESIS

Skeletal muscle architecture is the strongest predictor of a muscle's functional capacity. The purpose of this study was to define the architectural properties of the deep muscles of the female pelvic floor (PFMs) to elucidate their structure-function relationships.

METHODS

PFMs coccygeus (C), iliococcygeus (IC), and pubovisceral (PV) were harvested en bloc from ten fixed human cadavers (mean age 85 years, range 55-102). Fundamental architectural parameters of skeletal muscles [physiological cross-sectional area (PCSA), normalized fiber length, and sarcomere length (L(s))] were determined using validated methods. PCSA predicts muscle-force production, and normalized fiber length is related to muscle excursion. These parameters were compared using repeated measures analysis of variance (ANOVA) with post hoc t tests, as appropriate. Significance was set to α = 0.05.

RESULTS

PFMs were thinner than expected based on data reported from imaging studies and in vivo palpation. Significant differences in fiber length were observed across PFMs: C = 5.29 ± 0.32 cm, IC = 7.55 ± 0.46 cm, PV = 10.45 ± 0.67 cm (p < 0.001). Average L(s) of all PFMs was short relative to the optimal L(s) of 2.7 μm of other human skeletal muscles: C = 2.05 ± 0.02 μm, IC = 2.02 ± 0.02 μm, PC/PR = 2.07 ± 0.01 μm (p = <0.001 compared with 2.7 μm; p = 0.15 between PFMs, power = 0.46). Average PCSA was very small compared with other human muscles, with no significant difference between individual PFMs: C = 0.71 ± 0.06 cm(2), IC = 0.63 ± 0.04 cm(2), PV = 0.59 ± 0.05 cm(2) (p = 0.21, power = 0.27). Overall, C had shortest fibers, making it a good stabilizer. PV demonstrated the longest fibers, suggesting that it functions to produce large excursions.

CONCLUSIONS

PFM design shows individual muscles demonstrating differential architecture, corresponding to specialized function in the pelvic floor.

Does age affect visualization of the levator ani in nulliparous women?

INTRODUCTION AND HYPOTHESIS

Our aim was to assess whether differences in the ages of nulliparous women affect: (1) interobserver reliability, and (2) visualization of the levator ani (LA) muscle subdivisions in nulliparous women using 3D endovaginal ultrasound (3D-EVUS).

METHODS

This was a cross-sectional study. Community-dwelling nulliparous women ages 21-70 years were recruited. Participants underwent a standard examination and a 3D-EVUS. LA subdivisions of interest included the puboperinealis, puboanalis, pubococcygeus, puborectalis, and ileococcygeus muscles. Each ultrasound (US) volume was scored using a validated scale and assessed by two observers. Defect severity was scored for each muscle from 0 (no defect) to 6 (complete muscle loss). A summed score of the two sides was grouped as normal (0), minor (1-3), or major (4-6). Bias was examined using Bland-Altman plots. Intraclass coefficients were calculated to report agreement of total scores. Spearman's rank correlation was used to evaluate the association between age and LA scores.

RESULTS

Eighty nulliparous women were evaluated. Exact agreement for bilateral scoring of each LA subdivision ranged from 82 % to 84 %. Bilateral scoring of the puboperinealis, puborectalis, and ileococcygeus showed moderate to substantial agreement. Bilateral scores of the puboperinealis demonstrated substantial agreement between observers, with an ICC of 0.8 and a mean difference of -0.2 using the Bland-Altman analysis. When women were analyzed by age decade, reader agreement was overall good to excellent. There was no significant correlation between increasing age and total LA muscle scores (r = 0.179, p = 0.113).

CONCLUSIONS

Interobserver reliability or visualization of the LA muscle in nulliparous women was not affected by a woman's age.

New insights into the pelvic organ support framework

OBJECTIVE

It is important to understand the underlying mechanisms of the physiological framework of the pelvic organ support system to develop more effective interventions. Developing more successful interventions for restoration of defects of the pelvic floor will lead to symptomatic improvement of pelvic floor prolapse and stress incontinence disorders. The purpose of the current study was to investigate the physiological framework related to the pelvic organ support system and propose the underlying mechanisms of pelvic organ support based on the anatomical findings.

STUDY DESIGN

Ten female soft embalmed cadavers were dissected after a colorectal hands-on workshop to visualize components of the pelvic organ support system.

RESULTS

The puborectalis attached at the superior pubic ramus above the arcus tendineus fasciae pelvis. The anterior half of the iliococcygeus originated at the level of the arcus tendineus fasciae pelvis but descended from the arcus tendineus fasciae pelvis before it reached the ischial spine. The fibrous visceral sheath of the endopelvic fascia covered both the bladder and the upper vagina and bound these structures together. The levator ani muscle was separated into a horizontal and a vertical part at the medial attachment of the fibrous visceral sheath. A well-circumscribed adipose cushion pillow, in the ischioanal fossa and its anterior recess, supported the horizontal part of the levator ani muscle and pressed the vertical part against the pelvic viscera. Perivascular sheaths and pelvic nerve plexuses were reinforced by condensed endopelvic fascia, they suspended the pelvic organs posterolaterally.

CONCLUSION

The pelvic organ support framework consists of two mechanical structures: (1) the supporting system of the levator ani muscle, the arcus tendineus fasciae pelvis and the adipose cushion pillow, and (2) the suspension system of the neurovascular structures and the associated endopelvic fascia condensation.