The internal innervation and morphology of the human female levator ani muscle

Relationship between high intra-abdominal pressure and compliance of the pelvic floor support system in women without pelvic organ prolapse: A finite element analysis

Previous studies mainly focused on the relationship between the size of the prolapse and injury to the supporting tissues, but the strain and stress distributions of the supporting tissues as well as high-risk areas of injury are still unknown. To further investigate the effect of supporting tissues on organs and the interactions between organs, this study focused on the relationship between high intra-abdominal pressure and the compliance of the pelvic floor support system in a normal woman without pelvic organ prolapse (POP), using a finite element model of the whole pelvic support system. A healthy female volunteer (55 years old) was scanned using magnetic resonance imaging (MRI) during rest and Valsalva maneuver. According to the pelvic structure contours traced by a gynecologist and anatomic details measured from dynamic MRI, a finite element model of the whole pelvic support system was established, including the uterus, vagina with cavity, cardinal and uterosacral ligaments, levator ani muscle, rectum, bladder, perineal body, pelvis, and obturator internus and coccygeal muscles. This model was imported into ANSYS software, and an implicit iterative method was employed to simulate the biomechanical response with increasing intra-abdominal pressure. Stress and strain distributions of the vaginal wall showed that the posterior wall was more stable than the anterior wall under high intra-abdominal pressure. Displacement at the top of the vagina was larger than that at the bottom, especially in the anterior–posterior direction. These results imply potential injury areas with high intra-abdominal pressure in non-prolapsed women, and provide insight into clinical managements for the prevention and surgical repair plans of POP.

Localization of the nerves innervating the pelvic floor muscles: an application to pelvic pain treatment

INTRODUCTION

The aim of this study was to achieve accurate localization of the body surface position and depth of the center of the intramuscular nerve dense region (CINDR) of the pelvic floor muscles and to establish a target site for treating pelvic floor muscle spasm or weakness.

MATERIALS AND METHODS

Thirty-six adult cadavers were studied in the prone position. To locate the CINDR of the levator ani and coccygeus muscles, horizontal (H) and longitudinal (L) reference lines were used. Sihler's staining revealed the intramuscular nerve dense region of the pelvic floor muscles. The CINDR was labeled with barium sulfate and spiral computed tomography scanning, and three-dimensional reconstructions were obtained. The anterior and posterior CINDR projection points (P and P'), the position of point P projected on to the H and L lines (P_H and P_L ), and the CINDR depth were determined using the Syngo system.

RESULTS

The P_H of the CINDR of the levator ani and the coccygeus muscle were located at (24.73±0.17)% and (15.93±0.31)% of the H line, respectively. The P_L were located at (84.30±2.47)% and (6.76±0.93)% of the L line. The puncture depth of the levator ani muscle was located at (5.56±0.53) cm, and the depth of the coccygeus muscle at (22.08±2.11)% of the PP' line.

CONCLUSIONS

The body surface position and depth of the CINDR of the pelvic floor muscles were conducive to locating the target more efficiently and enhancing the efficacy of botulinum toxin A injection for treating pelvic floor muscle spasm and weakness with electrical stimulation or biofeedback. This article is protected by copyright. All rights reserved.

Correlation between pelvic floor ultrasound parameters and vaginal pressures in nulliparous women: a subanalysis of the SUM-AN study

INTRODUCTION AND HYPOTHESIS

Pelvic floor ultrasound is used as a validated technique for measuring levator ani dimensions. Vaginal manometry has been used in the past as a method to assess levator ani muscle (LAM) strength. Whether the combination of both methods can contribute to our understanding of pelvic floor pathophysiology has not yet been described. We hypothesized that as female pelvic floor muscular hiatus increases, the vaginal pressure and strength decrease.

METHODS

We recruited 20 asymptomatic nulliparous women ages 18-85 years. Minimal levator hiatus (MLH) area, anteroposterior/left-right (AP/LR) diameter ratio, the distance between levator plate and the pubic symphysis (LP-PS) while at rest and squeeze were measured using endovaginal ultrasound (US). Vaginal pressure at rest, squeeze (Kegel) and Valsalva were measured using 3D manometry. Logistic and linear regression analysis was performed to assess correlations.

RESULTS

MLH area was negatively correlated with the sum of all the squeeze pressures produced on the four walls of the vagina (p = 0.049, R² = 0.197). There was also a borderline negative correlation between MLH and the sum of rest pressures (p = 0.09, R² = 0.15). AP/LR ratio was negatively correlated with the sum of squeeze pressures (p = 0.056, R² = 0.197). LP-PS distances, both while at rest and during squeeze, were negatively correlated with the vaginal squeeze pressure (p = 0.046, R² = 0.21; p = 0.011, R² = 0.31, respectively). LP-V distance, both at rest and during squeeze, was negatively correlated with the sum of squeeze pressures on four vaginal walls (p = 0.02, R² = 0.25; p = 0.005, R² = 0.36, respectively).

CONCLUSIONS

Stronger levator ani muscles, smaller MLH area and a more oval shape of pelvic floor hiatus as assessed by pelvic floor ultrasound are associated with higher squeeze vaginal pressures as assessed by 3D manometry.

Ultrasonographic Imaging of the Pelvic Floor

This article discusses various pelvic floor ultrasonographic modalities and the clinical applications of ultrasonography of the pelvic floor. Ultrasonography provides a detailed anatomic assessment of the muscles and surrounding organs of the pelvic floor. Different anatomic variabilities and pathologic conditions, such as prolapse, fecal incontinence, urinary symptoms, vaginal wall cysts, synthetic implanted material, and pelvic pain, are assessed with pelvic floor ultrasonography. This imaging modality is an important adjunct to the evaluation and diagnosis of pelvic floor disorders.

Levator plate descent angle in pelvic floor disorders

BACKGROUND

The levator plate descent angle (LPDA) quantifies the levator plate position with reference to the pubic bone and perineal body at rest. Unfortunately, research on this notable new parameter is lacking, but it is clear that levator ani deficiency (LAD) will undermine the fundamental role of the levator ani muscle (LAM) in organ support. The aim of this study was to establish the relationship between the LPDA and LAD in patients with pelvic floor disorders.

METHODS

This retrospective study was conducted at Seoul Songdo Hospital, Korea between August 2019 and August 2020 on women with symptoms of pelvic floor disorder such as urinary incontinence, constipation, and fecal incontinence. In all cases, three-dimensional pelvic floor ultrasound was performed for LAD scoring, minimal levator hiatus, and LPDA evaluation. We evaluated LAD using a scoring system that graded levator injury according to the insertion point of each subdivision scored unilaterally. For the entire LAM group, a cumulative LAD score that ranged between 0 and 18 was possible. Scores were categorized as mild (0-6 points), moderate (7-12 points), and severe (13-18 points) deficiency RESULTS: A total of 93 patients were included in the study (mean age 65.89 ± 11.12 [range, 34-86] years). Thirteen participants had mild LAD scores (14.0%), 42 had moderate LAD scores (45.2%), and 38 had severe LAD scores (40.9%). There was a significant difference in mean age (59.23 ± 12.55 years vs. 64.43 ± 10.03 vs. 69.79 ± 10.55 years, p = 0.005) and mean parity (1.85 ± 0.90 vs 2.48 ± 1.15 vs 2.76 ± 1.10, p = 0.038) of patients between groups. There was also a significant difference in the mean Wexner incontinence score (7.14 ± 3.63 vs 7.24 ± 5.76 vs 11.41 ± 5.54, p = 0.028) and in the mean fecal incontinence quality of life (FIQOL) score (12.91 ± 3.11 vs 14.10 ± 3.87 vs 10.41 ± 3.65, p = 0.014). The mean value of the LPDA in the group with mild LAD scores was 14.65° (SD ± 3.54) and in the group with moderate LAD scores was 9.66° (SD ± 3.36). In the group with severe LAD scores, the mean LPDA was 1.83° (SD ± 4.71). The mean value for minimal levator hiatus (MLH) area in the mild LAD score group was 14.16cm² (SD ± 2.72), that in the moderate LAD score group was 15.82cm² (SD ± 2.30), and that in the severe LAD score group was 17.99cm² (SD ± 2.81). There were significant differences between the three groups both in decreasing LPDA (p < 0.001) and increasing MLH (p < 0.001). There was a negative correlation between the LAD score and LPDA and the Pearson correlation coefficient was -0.528 (moderate correlation). There was a positive correlation between the LAD score and MLH, and the Pearson correlation coefficient was 0.303 (weak correlation).

CONCLUSIONS

The LAD score and LPDA have a moderate negative correlation. In patients with severe pelvic floor symptoms and extensive LAM injury, high LAD scores and low LPDA results were confirmed. In the treatment of patients with pelvic floor disorders, the LPDA seems to be a very useful parameter in determining the severity of structural defects.

Pelvic floor architectural defects in female patients with urge fecal incontinence versus passive fecal leakage: a dynamic ultrasound study

INTRODUCTION AND HYPOTHESIS

Fecal incontinence (FI) has two primary subtypes: urgency fecal incontinence (UFI) and passive fecal leakage (PFL). The pathophysiology underlying the subtypes is incompletely understood.

OBJECTIVES

To compare the bowel habits, physical examinations and pelvic floor anatomical defects in patients with UFI-dominant FI versus patients with PFL-dominant FI.

STUDY DESIGN

This is a retrospective cross-sectional study of female patients who presented with fecal incontinence symptoms to our tertiary urogynecology center. All subjects underwent a comprehensive history, physical examination, 3D-static pelvic floor ultrasound, and 2D-dynamic ultrasound of the posterior compartment. Patients with UFI-dominant FI were compared to patients with PFL-dominant FI.

RESULTS

One hundred forty-five patients were included in the analysis; 57 categorized as UFI-dominant FI, 69 PFL-dominant FI and 19 categorized as having "both" leakage patterns. In comparing bowel habits, patient with UFI-dominant FI had more frequent bowel movements (15.5 ± SD 13.0/week vs. 10.9 ± SD 7.6 /week, p = 0.022) and were more likely to have loose stools (48.2% vs. 26.1%, p = 0.01). No statistically significant differences were observed in the prevalence of external anal sphincter defect (11.3% vs. 17.2%, p = 0.38) or internal anal sphincter defect (11.3% vs. 19%, p = 0.26) between groups. Finally, patients with UFI-dominant FI had a higher incidence of rectal hypermobility (loss of rectal support on Valsalva) (58% vs. 36.9%, p = 0.025).

CONCLUSION

Patients with urge-predominant FI have increased frequency of bowel movements, looser stools, and increased rectal folding diagnosed via dynamic ultrasound as compared to patients with passive-dominant FI.

Novel Application of Photogrammetry to Quantify Fascicle Orientations of Female Cadaveric Pelvic Floor Muscles

Although critical for understanding and simulating pelvic floor muscle function and pathophysiology, the fascicle arrangements of the coccygeus and levator ani remain mostly undetermined. We performed close-range photogrammetry on cadaveric pelvic floor muscles to robustly quantify surface fascicle orientations. The pelvic floor muscles of 5 female cadavers were exposed through anatomic dissections, removed en bloc, and photographed from every required angle. Overlapping images were mapped onto in silico geometries and muscle fascicles were traced manually. Tangent vectors were calculated along each trace; interpolated to define continuous, 3D vector fields; and projected onto axial and sagittal planes to calculate angles with respect to the pubococcygeal line. Contralateral and ipsilateral pelvic floor muscles were compared within each donor (Kuiper's tests) and using mean values from all donors (William-Watsons tests). Contralateral muscles and all but one ipsilateral muscle pair differed significantly within each donor (p < 0.001). When mean values were considered collectively, no contralateral or ipsilateral statistical differences were found but all muscles compared differed by more than 10° on average. Close-range photogrammetry and subsequent analyses robustly quantified surface fascicle orientations of the pelvic floor muscles. The continuous, 3D vector fields provide data necessary for improving simulations of the female pelvic floor muscles.

Recommended standardized terminology of the anterior female pelvis based on a structured medical literature review

BACKGROUND

The use of imprecise and inaccurate terms leads to confusion amongst anatomists and medical professionals.

OBJECTIVE

We sought to create recommended standardized terminology to describe anatomic structures of the anterior female pelvis based on a structured review of published literature and selected text books.

STUDY DESIGN

We searched MEDLINE from its inception until May 2, 2016, using 11 medical subject heading terms to identify studies reporting on anterior female pelvic anatomy; any study type published in English was accepted. Nine textbooks were also included. We screened 12,264 abstracts, identifying 200 eligible studies along with 13 textbook chapters from which we extracted all pertinent anatomic terms.

RESULTS

In all, 67 unique structures in the anterior female pelvis were identified. A total of 59 of these have been previously recognized with accepted terms in Terminologia Anatomica, the international standard on anatomical terminology. We also identified and propose the adoption of 4 anatomic regional terms (lateral vaginal wall, pelvic sidewall, pelvic bones, and anterior compartment), and 2 structural terms not included in Terminologia Anatomica (vaginal sulcus and levator hiatus). In addition, we identified 2 controversial terms (pubourethral ligament and Grafenberg spot) that require additional research and consensus from the greater medical and scientific community prior to adoption or rejection of these terms.

CONCLUSION

We propose standardized terminology that should be used when discussing anatomic structures in the anterior female pelvis to help improve communication among researchers, clinicians, and surgeons.

Levator ani muscle innervation: Anatomical study in human fetus

AIMS

To characterize the nature and function of the levator ani muscle innervation pathways and to perform a comprehensive three-dimensional reconstruction of female pelvic innervation.

METHODS

A computer-assisted anatomical dissection protocol was applied to seven female human fetuses, after approval from the national biomedicine agency. Specimens were serially sectioned and immunostained for overall (antibody against protein S100), somatic (antibody against peripheral myelin protein 22), adrenergic (antibody against tyrosine hydroxylase), cholinergic (antibody against vesicular acetylcholine transferase), and nitrergic (antibody against the neural isoform of nitric oxide synthase) nerve fibers. Slides were digitized for three-dimensional reconstructions using WinSurf®.

RESULTS

Three main nerve pathways to the levator ani muscle were observed: the levator ani nerve, the pudendal nerve, and the inferior hypogastric plexus. The pudendal nerve was both somatic and autonomic, located below the levator ani muscle (infralevator pathway), supplying innervation to the inferior aspect of the levator ani muscle. The levator ani nerve was solely somatic, located above the levator ani muscle (supralevator pathway), supplying innervation to the superior aspect of the levator ani muscle. The inferior hypogastric plexus nerve fibers were solely autonomic, located in between the levator ani muscle and pelvic organs (endolevator pathway), supplying innervation to the medial portion of the levator ani muscle.

CONCLUSIONS

Our study provides a new representation of levator ani muscle innervation with three nerve pathways, and the levator ani muscle itself as an anatomical landmark.

[Anatomy of the levator ani muscle and implications for obstetrics and gynaecology]

Pelvic floor disorders include urogenital and anorectal prolapse, urinary and faecal incontinence. These diseases affect 25% of patients. Most of time, treatment is primarily surgical with a high post-operative risk of recurrence, especially for pelvic organ prolapse. Vaginal delivery is the major risk factor for pelvic floor disorders through levator ani muscle injury or nerve damage. After vaginal delivery, 20% of patients experiment elevator ani trauma. These injuries are more common in case of instrumental delivery by forceps, prolonged second phase labor, increased neonatal head circumference and associated anal sphincter injuries. Moreover, 25% of patients have temporary perineal neuropathy. Recently, pelvic three-dimensional reconstructions from RMI data allowed a better understanding of detailed levator ani muscle morphology and gave birth to a clear new nomenclature describing this muscle complex to be developed. Radiologic and anatomic studies have allowed exploring levator ani innervation leading to speculate on the muscle and nerve damage mechanisms during delivery. We then reviewed the levator ani muscle anatomy and innervation to better understand pelvic floor dysfunction observed after vaginal delivery.

Surgical repair of bilateral levator ani muscles with ultrasound guidance

Separation of the levator ani muscles from pubic bone is a common major levator trauma that may occur in vaginal delivery and is associated with pelvic floor dysfunctions. We describe a novel ultrasound-guided technique to repair these muscles. A 33-year-old woman presented with a history of difficult vaginal delivery and complaint of numbness and weakness of the vagina. In evaluation, bilateral levator defects were diagnosed by physical examination, three-dimensional endovaginal ultrasound, and magnetic resonance imaging. With ultrasound guidance the detached ends of muscles were tagged and sutured to their insertion points at the pubic bone. The patient's normal anatomy was restored with the return to normal pelvic floor tone. A follow-up ultrasound showed restored levator anatomy at 3 months.

In vivo visualization of the levator ani muscle subdivisions using MR fiber tractography with diffusion tensor imaging

Understanding the levator ani complex architecture is of major clinical relevance. The aim of this study was to determine the feasibility of magnetic resonance (MR) fiber tractography with diffusion tensor imaging (DTI) as a tool for the three-dimensional (3D) representation of normal subdivisions of the levator ani. Ten young nulliparous female volunteers underwent DTI at 1.5 T MR imaging. Diffusion-weighted axial sequence of the pelvic floor was performed with additional T2-weighted multiplanar sequences for anatomical reference. Fiber tractography for visualization of each Terminologia Anatomica-listed major levator ani subdivision was performed. Numeric muscular fibers extracted after tractography were judged as accurate when localized within the boundaries of the muscle, and inaccurate when projecting out of the boundaries of the muscle. From the fiber tracking of each subdivision the number of numeric fibers (inaccurate and accurate) and a score (from 3 to 0) of the adequacy of the 3D representation were calculated. All but two volunteers completed the protocol. The mean number of accurate fibers was 17 ± 2 for the pubovisceralis, 14 ± 6 for the puborectalis and 1 ± 1 for the iliococcygeus. The quality of the 3D representation was judged as good (score = 2) for the pubovisceralis and puborectalis, and inaccurate (score = 0) for the iliococcygeus. Our study is the first step to a 3D visualization of the three major levator ani subdivisions, which could help to better understand their in vivo functional anatomy.

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

AIMS

Functional tests have demonstrated minimal loss of vaginal closure force with age. So we tested the null hypotheses that age neither affects the maximum cross-sectional area (CSA) nor the volume of the levator muscle. Corresponding hypotheses were also tested in the adjacent obturator internus muscle, which served as a control for the effect of age on appendicular muscle in these women.

METHODS

Magnetic resonance images of 15 healthy younger (aged 21-25 years) and 12 healthy older nulliparous women (aged >63 years) were selected to avoid the confounding effect of childbirth. Models were created from tracing outlines of the levator ani muscle in the coronal plane, and obturator internus in the axial plane using 3D Slicer v. 3.4. Muscle volumes were calculated using Slicer, while CSA was measured using Imageware™ at nine locations. The hypotheses were tested using repeated measures analysis of variance with P < 0.05 being considered significant.

RESULTS

The effect of age did not reach statistical significance for the decrease in levator ani muscle maximum CSA or the decrease in volume (4.3%, P = 0.62 and 10.9%, 0.12, respectively). However, age did significantly adversely decrease obturator internus muscle maximum CSA and volume (24.5% and 28.2%, P < 0.001, respectively). Significant local age-related changes were observed dorsally in both muscles.

CONCLUSIONS

Unlike the adjacent appendicular muscle, obturator internus, the levator ani muscle in healthy nullipara does not show evidence of significant age-related atrophy.

A subject-specific anisotropic visco-hyperelastic finite element model of female pelvic floor stress and strain during the second stage of labor

OBJECTIVES

To develop an improved model representation of the biomechanics of the levator muscles during the second stage of labor and to use a sensitivity analysis to explore the pathomechanics of levator muscle injury.

METHODS

A subject-specific finite element model of human pelvic floor and fetal head was developed based on in vivo MRI data of a fetal head and maternal pelvis. An anisotropic visco-hyperelastic constitutive model employed material parameters estimated from biaxial tests on pelvic floor tissues. Boundary conditions reflected both anatomic constraints and the curve of Carus. A short second stage of labor, scaled to 10 min, was then simulated using a single expulsive push made in the absence of levator co-contraction.

RESULTS

Large levator stresses occurred near the levator hiatus reaching 9 MPa at the pubovisceral muscle enthesis. The dominant principal stresses were located at, and aligned with, the edge of the hiatus. Muscle stretch bordering the levator hiatus was inhomogeneous: the average levator stretch was 3.55 with a high of 4.64 at the pubovisceral muscle enthesis. Decreasing perineal body stiffness by 40%, 50%, and 60% led to reductions in the maximum principal stretch ratio at the pubovisceral muscle enthesis of 8%, 13%, and 18%, respectively.

CONCLUSIONS

The pubovisceral muscle enthesis and the muscle near the perineal body are the regions of greatest strain thereby placing them at highest risk for stretch-related injury. Decreasing perineal body tissue stiffness significantly reduced tissue stress and strain, and therefore injury risk, in those regions.

On the anatomy and histology of the pubovisceral muscle enthesis in women

AIMS

The origin of the pubovisceral muscle (PVM) from the pubic bone is known to be at elevated risk for injury during difficult vaginal births. We examined the anatomy and histology of its enthesial origin to classify its type and see if it differs from appendicular entheses.

METHODS

Parasagittal sections of the pubic bone, PVM enthesis, myotendinous junction, and muscle proper were harvested from five female cadavers (51-98 years). Histological sections were prepared with hematoxylin and eosin, Masson's trichrome, and Verhoeff-Van Gieson stains. The type of enthesis was identified according to a published enthesial classification scheme. Quantitative imaging analysis was performed in sampling bands 2 mm apart along the enthesis to determine its cross-sectional area and composition.

RESULTS

The PVM enthesis can be classified as a fibrous enthesis. The PVM muscle fibers terminated in collagenous fibers that insert tangentially onto the periosteum of the pubic bone for the most part. Sharpey's fibers were not observed. In a longitudinal cross-section, the area of the connective tissue and muscle becomes equal approximately 8 mm from the pubic bone.

CONCLUSION

The PVM originates bilaterally from the pubic bone via fibrous entheses whose collagen fibers arise tangentially from the periosteum of the pubic bone.

Surgical reconstitution of a unilaterally avulsed symptomatic puborectalis muscle using autologous fascia lata

BACKGROUND

The puborectalis muscle is an important muscle for the maintenance of fecal continence. We present a novel surgical technique for repair of symptomatic avulsed puborectalis muscle.

CASE

This woman presented with dyspareunia and fecal incontinence since the vaginal birth of her child 2 years before. The diagnosis of an avulsed right puborectalis was made by physical examination and confirmed by magnetic resonance imaging and three-dimensional ultrasonography. Fascia lata was harvested from the patient's thigh and used to reconstitute the missing portion of the puborectalis muscle. At 12 months postoperatively, the patient was continent of stool and relieved of dyspareunia.

CONCLUSION

The patient's dyspareunia and fecal incontinence were alleviated by restoring normal anatomy.