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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., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Pelvic floor disorders after childbirth have distressing lifelong consequences for women, requiring more than 300,000 women to have surgery annually. This represents approximately 10% of the 3 million women who give birth vaginally each year. Vaginal birth is the largest modifiable risk factor for prolapse, the pelvic floor disorder most strongly associated with birth, and is an important contributor to stress incontinence. These disorders require 10 times as many operations as anal sphincter injuries. Imaging shows that injuries of the levator ani muscle, perineal body, and membrane occur in up to 19% of primiparous women. During birth, the levator muscle and birth canal tissues must stretch to more than 3 times their original length; it is this overstretching that is responsible for the muscle tear visible on imaging rather than compression or neuropathy. The injury is present in 55% of women with prolapse later in life, with an odds ratio of 7.3, compared with women with normal support. In addition, levator damage can affect other aspects of hiatal closure, such as the perineal body and membrane. These injuries are associated with an enlarged urogenital hiatus, now known as antedate prolapse, and with prolapse surgery failure. Risk factors for levator injury are multifactorial and include forceps delivery, occiput posterior birth, older maternal age, long second stage of labor, and birthweight of >4000 g. Delivery with a vacuum device is associated with reduced levator damage. Other steps that might logically reduce injuries include manual rotation from occiput posterior to occiput anterior, slow gradual delivery, perineal massage or compresses, and early induction of labor, but these require study to document protection. In addition, teaching women to avoid pushing against a contracted levator muscle would likely decrease injury risk by decreasing tension on the vulnerable muscle origin. Providing care for women who have experienced difficult deliveries can be enhanced with early recognition, physical therapy, and attention to recovery. It is only right that women be made aware of these risks during pregnancy. Educating women on the long-term pelvic floor sequelae of childbirth should be performed antenatally so that they can be empowered to make informed decisions about management decisions during labor., (Copyright © 2023 Elsevier Inc. All rights reserved.)

The uterine suspensory tissue (UST) complex includes the cardinal (CL) and uterosacral "ligaments" (USL), which are mesentery-like structures that play a role in resisting pelvic organ prolapse (POP). Since there is no information on the time-dependent material properties of the whole structure in situ and in vivo, we developed and tested an intraoperative technique to quantify in vivo whether there is a significant difference in visco-hyperelastic behavior of the CL and USL between women with and without POP. Thirteen women with POP (cases) and four controls scheduled for surgery were selected from an ongoing POP study. Immediately prior to surgery, a computer-controlled linear servo-actuator with a series force transducer applied a continuous, caudally directed traction force while simultaneously recording the resulting cervical displacement in the same direction. After applying an initial 1.1 N preload, a ramp rate of 4 mm/s was used to apply a maximum force of 17.8 N in three "ramp-and-hold" test trials. A simplified bilateral four-cable biomechanical model was used to identify the material behavior of each ligament. For this, the initial cross-section areas of the CL and USL were measured on 3-T magnetic resonance image-based 3D models from each subject. The time-dependent strain energy function of CL/USL was defined with a three-parameter hyperelastic Mooney-Rivlin material model and a two-term Prony series in relaxation form. When cases were compared with controls, the estimated time-dependent material constants of CL and USL did not differ significantly. These are the first measurements that compare the in vivo and in situ visco-hyperelastic response of the tissues comprising the CL and USL to loading in women with and without prolapse. Larger sample sizes would help improve the precision of intergroup differences., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Background: During the second stage of labor, the maternal pelvic floor muscles undergo repetitive stretch loading as uterine contractions and strenuous maternal pushes combined to expel the fetus, and it is not uncommon that these muscles sustain a partial or complete rupture. It has recently been demonstrated that soft tissues, including the anterior cruciate ligament and connective tissue in sheep pelvic floor muscle, can accumulate damage under repetitive physiological (submaximal) loads. It is well known to material scientists that this damage accumulation can not only decrease tissue resistance to stretch but also result in a partial or complete structural failure. Thus, we wondered whether certain maternal pushing patterns (in terms of frequency and duration of each push) could increase the risk of excessive damage accumulation in the pelvic floor tissue, thereby inadvertently contributing to the development of pelvic floor muscle injury., Objective: This study aimed to determine which labor management practices (spontaneous vs directed pushing) are less prone to accumulate damage in the pelvic floor muscles during the second stage of labor and find the optimum approach in terms of minimizing the risk of pelvic floor muscle injury., Study Design: We developed a biomechanical model for the expulsive phase of the second stage of labor that includes the ability to measure the damage accumulation because of repetitive physiological submaximal loads. We performed 4 simulations of the second stage of labor, reflecting a directed pushing technique and 3 alternatives for spontaneous pushing., Results: The finite element model predicted that the origin of the pubovisceral muscle accumulates the most damage and so it is the most likely place for a tear to develop. This result was independent of the pushing pattern. Performing 3 maternal pushes per contraction, with each push lasting 5 seconds, caused less damage and seemed the best approach. The directed pushing technique (3 pushes per contraction, with each push lasting 10 seconds) did not reduce the duration of the second stage of labor and caused higher damage accumulation., Conclusion: The frequency and duration of the maternal pushes influenced the damage accumulation in the passive tissues of the pelvic floor muscles, indicating that it can influence the prevalence of pelvic floor muscle injuries. Our results suggested that the maternal pushes should not last longer than 5 seconds and that the duration of active pushing is a better measurement than the total duration of the second stage of labor. Hopefully, this research will help to shed new light on the best practices needed to improve the experience of labor for women., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Background: One of the major causes of pelvic organ prolapse is pelvic muscle injury sustained during a vaginal delivery. The most common site of this injury is where the pubovisceral muscle takes origin from the pubic bone. We hypothesized that it is possible for low-cycle material fatigue to occur at the origin of the pubovisceral muscle under the large repetitive loads associated with pushing during the second stage of a difficult labor., Purpose: The main goal was to test if the origin of the pubovisceral muscle accumulates material damage under sub-maximal cyclic tensile loading and identify any microscopic evidence of such damage., Methods: Twenty origins of the ishiococcygeous muscle (homologous to the pubovisceral muscle in women) were dissected from female sheep pelvises. Four specimens were stretched to failure to characterize the failure properties of the specimens. Thirteen specimens were then subjected to relaxation and subsequent fatigue tests, while three specimens remained as untested controls. Histology was performed to check for microscopic damage accumulation., Results: The fatigue stress-time curves showed continuous stress softening, a sign of material damage accumulation. Histology confirmed the presence of accumulated microdamage in the form of kinked muscle fibers and muscle fiber disruption in the areas with higher deformation, namely in the muscle near the musculotendinous junction., Conclusions: The origin of ovine ishiococcygeous muscle can accumulate damage under sub-maximal repetitive loading. The damage appears in the muscle near the musculotendinous junction and was sufficient to negatively affect the macroscopic mechanical properties of the specimens., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Background: Vaginal birth is a risk factor for pubovisceral muscle tear, decreased urethral closure pressure, and urinary incontinence. The relationship between these 3 factors is complicated. Urinary continence relies on maintaining urethral closure pressure, particularly when low urethral closure pressure can usefully be augmented by a volitional pelvic muscle (Kegel) contraction just before and during stress events like a cough. However, it is unknown whether a torn pubovisceral muscle decreases the ability to increase urethral closure during an attempted pelvic muscle contraction., Objective: We tested the null hypothesis that a pubovisceral muscle tear does not affect the ability to increase urethral closure pressure during a volitional pelvic muscle contraction in the Evaluating Maternal Recovery from Labor and Delivery (EMRLD) study., Study Design: We studied 56 women 8 months after their first vaginal birth. All had at least 1 risk factor for pubovisceral muscle tear (eg, forceps and long second stage). A tear was assessed bilaterally by magnetic resonance imaging. Urethral closure pressure was measured both at rest and during an attempted volitional pelvic muscle contraction. A Student t test was used to compare urethral closure pressures. Multiple linear regression was used to estimate the effect of a magnetic resonance imaging-confirmed pubovisceral muscle tear on volitionally contracted urethral closure pressure after adjusting for resting urethral closure pressure., Results: The mean age was just a little more than 30 years, with the majority being white. By magnetic resonance imaging measure, unadjusted for other factors, the 21 women with tear had significantly lower urethral closure pressure during an attempted contraction compared with the 35 women without tear (65.9 vs 86.8 cm H 2 O, respectively, P = .004), leading us to reject the null hypothesis. No significant group difference was found in resting urethral closure pressure. After adjusting for resting urethral closure pressure, pubovisceral muscle tear was associated with lower urethral closure pressure (beta = -21.1, P = .001)., Conclusion: In the first postpartum year, the presence of a pubovisceral muscle tear did not influence resting urethral closure. However, women with a pubovisceral muscle tear achieved a 25% lower urethral closure pressure during an attempted pelvic muscle contraction than those without a pubovisceral muscle tear. These women with pubovisceral muscle tear may not respond to classic behavioral interventions, such as squeeze when you sneeze or strengthen through repetitive pelvic muscle exercises. When a rapid rise to maximum urethral pressure is used as a conscious volitional maneuver, it appears to be reliant on the ability to recruit the intact pubovisceral muscle to simultaneously contract the urethral striated muscle., (Copyright © 2019 Elsevier Inc. All rights reserved.)

To explain the pathophysiology of pelvic organ prolapse, we must first understand the complexities of the normal support structures of the uterus and vagina. In this review, we focus on the apical ligaments, which include the cardinal and uterosacral ligaments. The aims of this review are the following: (1) to provide an overview of the anatomy and histology of the ligaments; (2) to summarize the imaging and biomechanical studies of the ligament properties and the way they relate to anterior and posterior vaginal wall prolapse; and (3) to synthesize these findings into a conceptual model for the progression of prolapse., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Although non-contact human ACL tears are a common knee injury, little is known about why they usually fail near the femoral enthesis. Recent histological studies have identified a range of characteristic femoral enthesis tidemark profiles and ligament attachment angles. We tested the effect of the tidemark profile and attachment angle on the distribution of strain across the enthesis, under a ligament stretch of 1.1. We employed a 2D analytical model followed by 3D finite element models using three constitutive forms and solved with ABAQUS/Standard. The results show that the maximum equivalent strain was located in the most distal region of the ACL femoral enthesis. It is noteworthy that this strain was markedly increased by a concave (with respect to bone) entheseal profile in that region as well as by a smaller attachment angle, both of which are features more commonly found in females. Although the magnitude of the maximum equivalent strain predicted was not consistent among the constitutive models used, it did not affect the relationship observed between entheseal shape and maximum equivalent strain. We conclude that a concave tidemark profile and acute attachment angle at the femoral ACL enthesis increase the risk for ACL failure, and that failure is most likely to begin in the most distal region of that enthesis., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

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, τ 2 , 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., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Background: It is unknown how initial cervix location and cervical support resistance to traction, which we term "apical support stiffness," compare in women with different patterns of pelvic organ support. Defining a normal range of apical support stiffness is important to better understand the pathophysiology of apical support loss., Objective: The aims of our study were to determine whether: (1) women with normal apical support on clinic Pelvic Organ Prolapse Quantification, but with vaginal wall prolapse (cystocele and/or rectocele), have the same intraoperative cervix location and apical support stiffness as women with normal pelvic support; and (2) all women with apical prolapse have abnormal intraoperative cervix location and apical support stiffness. A third objective was to identify clinical and biomechanical factors independently associated with clinic Pelvic Organ Prolapse Quantification point C., Study Design: We conducted an observational study of women with a full spectrum of pelvic organ support scheduled to undergo gynecologic surgery. All women underwent a preoperative clinic examination, including Pelvic Organ Prolapse Quantification. Cervix starting location and the resistance (stiffness) of its supports to being moved steadily in the direction of a traction force that increased from 0-18 N was measured intraoperatively using a computer-controlled servoactuator device. Women were divided into 3 groups for analysis according to their pelvic support as classified using the clinic Pelvic Organ Prolapse Quantification: (1) "normal/normal" was women with normal apical (C < -5 cm) and vaginal (Ba and Bp < 0 cm) support; (2) normal/prolapse had normal apical support (C < -5 cm) but prolapse of the anterior or posterior vaginal walls (Ba and/or Bp ≥ 0 cm); and (3) prolapse/prolapse had both apical and vaginal wall prolapse (C > -5 cm and Ba and/or Bp ≥ 0 cm). Demographics, intraoperative cervix locations, and apical support stiffness values were then compared. Normal range of cervix location during clinic examination and operative testing was defined by the total range of values observed in the normal/normal group. The proportion of women in each group with cervix locations within and outside the normal range was determined. Linear regression was performed to identify variables independently associated with clinic Pelvic Organ Prolapse Quantification point C., Results: In all, 52 women were included: 14 in the normal/normal group, 11 in the normal/prolapse group, and 27 in the prolapse/prolapse group. At 1 N of traction force in the operating room, 50% of women in the normal/prolapse group had cervix locations outside the normal range while 10% had apical support stiffness outside the normal range. Of women in the prolapse/prolapse group, 81% had cervix locations outside the normal range and 8% had apical support stiffness outside the normal range. Similar results for cervix locations were observed at 18 N of traction force; however the proportion of women with apical support stiffness outside the normal range increased to 50% in the normal/prolapse group and 59% in the prolapse/prolapse group. The prolapse/prolapse group had statistically lower apical support stiffness compared to the normal/normal group with increased traction from 1-18 N (0.47 ± 0.18 N/mm vs 0.63 ± 0.20 N/mm, P = .006), but all other comparisons were nonsignificant. After controlling for age, parity, body mass index, and apical support stiffness, cervix location at 1 N traction force remained an independent predictor of clinic Pelvic Organ Prolapse Quantification point C, but only in the prolapse/prolapse group., Conclusion: Approximately 50% of women with cystocele and/or rectocele but normal apical support in the clinic had cervix locations outside the normal range under intraoperative traction, while 19% of women with uterine prolapse had normal apical support. Identifying women whose apical support falls outside a defined normal range may be a more accurate way to identify those who truly need a hysterectomy and/or an apical support procedure and to spare those who do not., Competing Interests: The authors report no conflict of interest., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Valgus knee angle (VKA) maybe a predictor of non-contact anterior cruciate ligament (ACL) injuries. Pre-programmed muscle activation strategies may exist which could contribute to the larger VKA displayed in women compared to men. The current study examined the relationship between the peak VKA and preparatory muscle activity. Twenty-one adults were asked to perform five trials of a forward hop. Lower extremity kinematics and surface EMG were recorded. Peak VKA and EMG from 100ms prior to ground contact were used in the data analyses. Three multiple linear regressions, where muscle activity was regressed upon the peak VKA, were run using subsets (female, male, and male/female) of the sample. Partial regression coefficients were considered significant at P0.05. When female subjects were exclusively included in the model, a higher peak VKA was associated with increased preparatory vastus lateralis and lateral hamstring activity, while a lower VKA was associated with increased preparatory vastus medialis activity (P0.05). When both genders and males alone were considered, preparatory activity was not associated with peak VKA (P0.05). Neuromuscular training promoting equal preparatory muscle activity in the medial-to-lateral quadriceps and hamstrings may reduce the incidence of ACL injuries in females.

Objective: The purpose of this study was to determine the increase in pudendal nerve branch lengths using a 3D computer model of vaginal delivery., Study Design: The main inferior rectal and perineal branches of the pudendal nerve were dissected in 12 hemi-pelves from 6 adult female cadavers. Their 3D courses were digitized in the 4 specimens with the most characteristic nerve branching pattern, and the data were imported into a published 3D computer model of the pelvic floor. Each nerve branch was then represented by a stretchable cord with a fixation point at the ischial spine. The length change in each branch was then quantified as the fetal head descended through the pelvic floor. The maximum nerve strains ([final length minus original length/original length] x 100) were calculated for 5 degrees of perineal descent: reference descent from the literature, 1.25 cm and 2.5 cm caudal and cephalad. The effect of alternative fixation points on resultant nerve strain was also studied., Results: The inferior rectal branch exhibited the maximum strain, 35%, and this strain varied by 15% from the scenario with the least perineal descent to that with the most perineal descent. The strain in the perineal nerve branch innervating the anal sphincter reached 33%, while the branches innervating the posterior labia and urethral sphincter reached values of 15% and 13%, respectively. The more proximal the nerve fixation point, the greater the nerve strain., Conclusion: During the second stage: (1) nerves innervating the anal sphincter are stretched beyond the 15% strain threshold known to cause permanent damage in appendicular peripheral nerve, and (2) the degree of perineal descent is shown to influence pudendal nerve strain.

Objective: This study was undertaken to quantify resting vaginal closure force (VCF(REST)), maximum vaginal closure force (VCF(MAX)), and augmentation of vaginal closure force augmentation (VCF(AUG)) when supine and standing and to determine whether the change in intra-abdominal pressure associated with change in posture accounts for differences in VCF., Study Design: Thirty-nine asymptomatic, continent women were recruited to determine, when supine and standing, the vaginal closure force (eg, the force closing the vagina in the mid-sagittal plane) and bladder pressures at rest and at maximal voluntary contraction. VCF was measured with an instrumented vaginal speculum and bladder pressure was determined with a microtip catheter. VCF(REST) was the resting pelvic floor tone, and VCF(MAX) was the peak pelvic floor force during a maximal voluntary contraction. VCF(AUG) was the difference between VCF(MAX) and VCF(REST). T tests and Pearson correlation coefficients were used for analysis., Results: VCF(REST) when supine was 3.6 +/- 0.8 N and when standing was 6.9 +/- 1.5 N--a 92% difference (P < .001). The VCF(MAX) when supine was 7.5 +/- 2.9 N and when standing was 10.1 +/- 2.4 N--a 35% difference (P < .001). Bladder pressure when supine (10.5 +/- 4.7 cm H2O) was significantly less (P < .001) than when standing (31.0 +/- 6.4 cm H2O). The differences in bladder pressure when either supine or standing did not correlate with the corresponding differences in VCF at rest or at maximal voluntary contraction. The supine VCF(AUG) of 3.9 +/- 2.7 N, was significantly greater than the standing VCF(AUG) of 3.3+/-1.9 N., Conclusion: With change in posture, vaginal closure force increases because of higher intra-abdominal pressure and greater resistance in the pelvic floor muscles.

Objective: The purpose of this study was to determine if the ability to increase maximum urethral closure pressure (MUCP) with a pelvic muscle contraction is impaired in women without pubococcygeal muscle (PCM)., Study Design: This was a cross-sectional study of continent women comparing those with (n=28) and those without (n=17) PCM as identified by MR scans. A pelvic muscle contraction was performed simultaneously with recordings of urethral and bladder pressures., Results: Eighty-six percent of the women with PCM compared with 41% of the women without could volitionally increase (>5 cm H(2)O) their MUCP. Those with PCM generated a mean intraurethral pressure rise of 14.0 (10.8) cm H(2)O, compared with 6.2 (8.7) cm H(2)O in those without (P=.015). Among women who could produce a visible pressure rise, there was not a statistically significant difference between groups (with PCM=17.2 [7.8] cm H(2)O; without PCM=14.7 [7.5] cm H(2)O; P=.457)., Conclusion: Selective women without visible PCM can increase MUCP.

Objective: The purpose of this study was to develop a system to quantify interindividual variation in the appearance of continence system structures in normal continent nulliparous women., Study Design: Magnetic resonance imaging (1.5 T) was performed in 20 healthy continent nulliparous women (mean age, 30.1 +/- 5.1 years) with normal pelvic organ support and urodynamics. Morphometric measurements of the levator ani muscle, endopelvic fascia, and urethra were performed., Results: The ratio of the maximum-to-minimum measured values shows that 2- to 3-fold differences occur in distance, area, or volume measures of continence system morphologic features. The mean urogenital hiatus area was 15.2 +/- 2.9 cm(2) in women without a visible connection of the levator ani muscle to the pubic bone (4/20 women) and 12.3 +/- 2.4 cm(2) in women with an levator ani muscle-pubic bone connection (16/20 women, P =.05)., Conclusion: Considerable variation that was not attributable to limitations of the measuring technique that was used occurs in the size and configuration of the urethral support structures in nulliparous asymptomatic women.

Objective: This study tests the null hypothesis that the size of the pelvic opening spanned by the pelvic floor is the same in African American and European American women., Study Design: Forty African American female pelvises were age matched with 40 European American female pelvises from the Hamann-Todd collection at the Cleveland Museum of Natural History. The distances between the anchoring points of the pelvic floor to the bony pelvis (pubis anteriorly, ischial spines laterally, and inferior lateral angle of the sacrum posteriorly) were measured on each half of the pelvis. Measurements from left and right halves were averaged. The cross-sectional area of the pelvic floor was calculated from these dimensions. The bi-ischial line divided the total area into anterior and posterior pelvic floor areas. Analyses taking into account differences in stature by dividing individual dimensions by height were also performed. Group differences were compared with the Student t test and the Mann-Whitney rank sum test., Results: African American women had a 5.1% smaller pelvic floor area than European American women (889.6 cm(2) vs 937.0 cm(2), 5.1% P =.037). This was attributable to a 10.4% smaller posterior area (365.3 cm(2) vs 407.6 cm(2), 10.4% P =.016), whereas the anterior areas were similar (524.3 cm(2) vs 529.3 cm(2), P =.61). The following measured distances were smaller in African American women: ischial spine to inferior sacral angle (5.4 cm vs 5.9 cm, P =.016) and bi-ischial diameter (10.0 cm vs 10.6 cm, P =.004). These distances remained significant after height was controlled., Conclusions: In African American women, the posterior pelvic floor area is 10.4% smaller than in European American women, resulting in a 5.1% smaller total pelvic floor area.

Objective: The purpose of the study was to measure the thickness and cross-sectional area of urethral muscle layers to identify localized striated muscle loss., Study Design: The urethra and surrounding tissues from 25 female cadavers (mean age, 52 +/- 18 [SD] years; range, 15-80 years) were used for this study. Axial and median sagittal histologic sections were prepared. Median sagittal muscle layer thickness was measured every 10% of urethral length (each decile) in the dorsal wall (adjacent to the vagina) and ventral wall, beginning at the caudal margin of the detrusor muscle (0%) and ending at the caudal margin of the striated muscle (100%). In the midurethral cross-section, the thickness of each layer was measured along radial lines placed every 45 degrees with 0 degrees at the ventral midline and 180 degrees at the dorsal midline., Results: In the median sagittal sections, striated muscle layers of urethras were thinner at the vesical neck in older women. In the ventral wall, it decreased by a mean of 18 to 23 microm (3.4%-4.3%; P <.001) per year at 10% to 30% of urethral wall length. Dorsal striated muscle layers were thinner at every decile by 11 to 16 microm (3.2%-4.3%; P <.05); their total cross-sectional areas decreased by 0.19 mm2) (3.8%) per year short ( P <.001). In the midurethral cross-sections, the muscle was thinner by 16 to 25 microm (1.5% and 4.6%; P <.05) at 90, 135, and 180 degrees., Conclusion: Striated muscle was lost at the bladder neck and along the dorsal wall of the urethra as women aged.

Objective: This study was undertaken to test the null hypothesis that the number of striated muscle fibers in the ventral wall of the female urethra remains constant with increasing age., Study Design: The urethra and surrounding tissues from 25 female cadavers, mean age 52 years (+/-SD 18, range 15-80 years), were selected for this study. Each specimen was divided along the midsagittal plane, and a Masson trichrome histologic section was prepared. A systematic count of striated muscle fibers in the ventral wall was then obtained at each decile of urethral length., Results: A decrease in the total number of fibers within the sampled area was found with increasing age. The mean of the total fibers across all urethrae was 17,423 (+/-SD 9,624, range 4,788-35,867). Over the life span, an average of 364 fibers (2%) were lost per year (95% CI 197-531; P <.001). Mean fiber density was 671 (+/- SD 296, range 228-1374) fibers/mm2 and decreased by 13 fibers/mm2 per year (95% CI 8-17; P <.001). The mean lesser fiber diameter was 24 microm and did not change significantly with age ( P =.3)., Conclusions: The number and density of urethral striated muscle fibers decline with age.

Objective: We sought to develop a vector-based assessment to determine the magnitude and direction of bladder neck movements, as well as to assess whether probe movement relative to the pubis needs to be taken into account., Study Design: Ten nulliparous continent, 10 primiparous continent, and 10 primiparous stress-incontinent women were recruited. Perineal ultrasound scanning was performed in standing women while they were resting, performing the Valsalva maneuver, coughing, and performing Kegel exercises. A direct on-screen assessment of bladder neck displacement from rest to the peak of dynamic activity relative to the pubic axis was made. Transducer movement was assessed by measuring the displacement of the pubic bone., Results: The method was feasible because measurements were possible in all 30 subjects. Vesical neck and pubic point movement in millimeters (+/- SD) and the percentage error if pubic point movement is not accounted for are as follow: strain, vesical neck 16.9 +/- 6.1 and pubic point 4.8 +/- 3.9, 28%; cough, vesical neck 10.2 +/- 5.4, pubic point 2.9 +/- 3.4, 33%; Kegel exercise, vesical neck 7.0 +/- 3.6 and pubic point 0.7 +/- 1.4, 37%. Similar discrepancies in angle were found and are presented. Uncorrected direction of vesical neck and pubic point movement in degrees and the percentage error if pubic point movement is not accounted for are as follow: strain, vesical neck 169.4 +/- 18.5 and pubic point 214.0 +/- 56.7, 18%; cough, vesical neck 162.0 +/- 12.8, pubic point 238.4 +/- 27.4, 22%; Kegel exercise, vesical neck -0.9 +/- 12.7 and pubic point -4.8 +/- 20.6, 87%. Test-retest reliability correlations were more than an r value of 0.7 in all measures and 86% of the measurements greater than 0.8., Conclusion: The vector-based system provides a simple method for quantifying distance and direction of vesical neck motion, as well as localizing the resting vesical neck position.

Objective: A simplified geometric model of the uterine wall during the second and third stages of labor was created to estimate the magnitude of myometrial strain associated with the initiation of placental separation., Study Design: The uterine wall was modeled as an isovolumetric, incompressible spherical shell whose overall radius decreased and mural thickness increased on uterine muscle contraction after delivery of the fetus. Either a 3.5-MHz or a 5-MHz ultrasonography probe was used to measure the change in uterine mural thickness of 14 healthy patients from just before delivery to the time of initial separation of the placenta. The measured change in uterine wall thickness was then used to calculate its average radial and circumferential strain with a simple mathematic model., Results: Placental separation occurred at radial and circumferential strains (mean +/- SD) of 450% +/- 182% and -75% +/- 11%, respectively. These strains are consistent with the known maximal contractile strains achievable by smooth muscle., Conclusion: Placental separation is likely associated with maximal myometrial contractile strain. Before birth the presence of the fetal and amniotic fluid volumes usually renders such contractile strains unachievable, thereby helping to guard against premature placental separation.

The current study was undertaken to determine if age-related differences in muscle activities might relate to older adults being significantly less able than young adults to recover balance during a forward fall. Fourteen young and twelve older healthy males were released from forward leans of various magnitudes and asked to regain standing balance by taking a single forward step. Myoelectric signals were recorded from 12 lower extremity muscles and processed to compare the muscle activation patterns of young and older adults. Young adults successfully recovered from significantly larger leans than older adults using a single step (32.2 degrees vs. 23.5 degrees ). Muscular latency times, the time between release and activity onset, ranged from 73 to 114 ms with no significant age-related differences in the shortest muscular latency times. The overall response muscular activation patterns were similar for young and older adults. However older adults were slower to deactivate three stance leg muscles and also demonstrated delays in activating the step leg hip flexors and knee extensors prior to and during the swing phase. In the forward fall paradigm studied, age-differences in balance recovery performance do not seem due to slowness in response onset but may relate to differences in muscle activation timing during the stepping movement.

Mouth opening was measured in 43 children anaesthetized with isoflurane and paralysed with vecuronium or suxamethonium. Measurements of mouth opening were made for up to 10 min after loss of the adductor pollicis twitch and cessation of muscle fasciculations. In 22 patients receiving suxamethonium, a significant (P less than 0.001) reduction in mean mouth opening occurred in the 60 s after loss of twitch and cessation of fasciculations. Mouth opening reductions could last for up to 10 min after the loss of twitch, beyond the return of the twitch. One patient experienced "masseter spasm"; he did not develop malignant hyperpyrexia during 2.5 h of isoflurane anaesthesia. Patients receiving vecuronium showed a significant (P less than 0.0006) increase in mouth opening. In 20 subjects, mouth opening was generated with a small (1.67 N) and a larger (4.32 N) force. Proportionally equal reductions in mouth opening were obtained with either force after suxamethonium administration. Relatively equal increases with either force followed vecuronium administration. Isolated masseter spasm is not pathognomonic for malignant hyperpyrexia. If the diagnosis of malignant hyperpyrexia is contemplated, signs of hypermetabolism, such as increases in end-tidal carbon dioxide concentration during constant minute ventilation, should be sought.