On the Anatomy and Histology of the Pubovisceral Muscle Enthesis in Women

Article (PDF Available)inNeurourology and Urodynamics 30(7):1366-70 · September 2011with60 Reads
DOI: 10.1002/nau.21032 · Source: PubMed
Abstract
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. 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. 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. The PVM originates bilaterally from the pubic bone via fibrous entheses whose collagen fibers arise tangentially from the periosteum of the pubic bone.

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    • "To create the LAM model, three pairs of LAMs, based on existing descriptions [14], were included. The PVm and puborectal muscle (PRm) originate from the fibrous enthesis on the dorsal surface of the pubic bone [16, 17]. This section of the muscle is translationally and rotationally fixed. "
    [Show abstract] [Hide abstract] ABSTRACT: Introduction and hypothesisDuring vaginal delivery, the levator ani muscle (LAM) undergoes severe deformation. This stress can lead to stretch-related LAM injuries. The objective of this study was to develop a sophisticated MRI-based model to simulate changes in the LAM during vaginal delivery. MethodsA 3D finite element model of the female pelvic floor and fetal head was developed. The model geometry was based on MRI data from a nulliparous woman and 1-day-old neonate. Material parameters were estimated using uniaxial test data from the literature and by least-square minimization method. The boundary conditions reflected all anatomical constraints and supports. A simulation of vaginal delivery with regard to the cardinal movements of labor was then performed. ResultsThe mean stress values in the iliococcygeus portion of the LAM during fetal head extension were 4.91–7.93 MPa. The highest stress values were induced in the pubovisceral and puborectal LAM portions (mean 27.46 MPa) at the outset of fetal head extension. The last LAM subdivision engaged in the changes in stress was the posteromedial section of the puborectal muscle. The mean stress values were 16.89 MPa at the end of fetal head extension. The LAM was elongated by nearly 2.5 times from its initial resting position. Conclusions The cardinal movements of labor significantly affect the subsequent heterogeneous stress distribution in the LAM. The absolute stress values were highest in portions of the muscle that arise from the pubic bone. These areas are at the highest risk for muscle injuries with long-term complications.
    Full-text · Article · Aug 2016
    • "(ii) The PVM takes origin from the pubic bone bilaterally at bony entheses [17,18] and is comprised of striated muscle which inserts into the PB and smooth and striated muscle of the internal and external AS, respectively, in the intersphincteric groove, which is located between these sphincters (Fig. 2 ). Using the above assumptions, we calculate SL as follows: (2) Maternal capacity in the ultimate crowned state (a) We found that the PRM origin on the PM was so low that no wrapping of the PRM would occur about the inferior pubic rami in the downward rotation observed during birth. "
    [Show abstract] [Hide abstract] ABSTRACT: Because levator ani muscle injuries occur in approximately 13% of all vaginal births, insights are needed to better prevent them. In Part I of this paper we conducted an analysis of the bony and soft tissue factors contributing to the geometric 'capacity' of the maternal pelvis and pelvic floor to deliver a fetal head without incurring stretch injury of the maternal soft tissue. In Part II we quantified the range in demand, represented by the variation in fetal head size and shape, placed on the maternal pelvic floor. In Part III we analyzed the capacity-to-demand geometric ratio, g, in order to determine whether a mother can deliver a head of given size without stretch injury. The results of a Part I sensitivity analysis showed that initial soft tissue loop length had the greatest effect on maternal capacity, followed by the length of the soft tissue loop above the inferior pubic rami at ultimate crowning, then subpubic arch angle and head size, and finally the levator origin separation distance. We found the more caudal origin of the puborectal portion of the levator muscle helps to protect it from the stretch injuries commonly observed in the pubvisceral portion. In Part II fetal head molding index and fetal head size revealed fetal head circumference values ranging from 253 to 351 mm, which would increase up to 11 mm upon face presentation. The Part III capacity-demand analysis of g revealed that, based on geometry alone, the 10th percentile maternal capacity predicted injury for all head sizes, the 25th percentile maternal capacity could deliver half of all head sizes, while the 50th percentile maternal capacity could deliver a head of any size without injury. If ultrasound imaging could be operationalized to make measurements of ratio g it might be used to usefully inform women on their level risk for levator injury during vaginal birth.
    Article · Jan 2016
  • [Show abstract] [Hide abstract] ABSTRACT: 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. 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. 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. 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.
    Article · Dec 2011
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