Hiatal failure: effects of pregnancy, delivery, and pelvic floor disorders on level III factors

Abstract

Introduction and hypothesis: The failure of the levator hiatus (LH) and urogenital hiatus (UGH) to remain closed is not only associated with pelvic floor disorders, but also contributes to recurrence after surgical repair. Pregnancy and vaginal birth are key events affecting this closure. An understanding of normal and failed hiatal closure is necessary to understand, manage, and prevent pelvic floor disorders.

Methods: This narrative review was conducted by applying the keywords "levator hiatus" OR "genital hiatus" OR "urogenital hiatus" in PubMed. Articles that reported hiatal size related to pelvic floor disorders and pregnancy were chosen. Weighted averages for hiatal size were calculated for each clinical situation.

Results: Women with prolapse have a 22% and 30% larger LH area measured by ultrasound at rest and during Valsalva than parous women with normal support. Women with persistently enlarged UGH have 2-3 times higher postoperative failure rates after surgery for prolapse. During pregnancy, the LH area at Valsalva increases by 29% from the first to the third trimester in preparation for childbirth. The enlarged postpartum hiatus recovers over time, but does not return to nulliparous size after vaginal birth. Levator muscle injury during vaginal birth, especially forceps-assisted, is associated with increases in hiatal size; however, it only explains a portion of hiatus variation-the rest can be explained by pelvic muscle function and possibly injury to other level III structures.

Conclusions: Failed hiatal closure is strongly related to pelvic floor disorders. Vaginal birth and levator injury are primary factors affecting this important mechanism.

Keywords: Levator hiatus; Pelvic floor disorders; Pregnancy; Urogenital hiatus; Vaginal delivery.

Fig 1.. Cadaver dissection of the female pelvic floor

a) View from above after removal of the upper pelvic organs. b) Closeup view. Shown are the borders of the LH (dotted line) and the UGH (solid line). c) Left lateral view of the pelvis, showing antero-posterior diameters of LH (dotted line) and UGH (solid line). LH, levator hiatus; UGH, urogenital hiatus; CM, coccygeus muscle; ICM, iliococcygeal muscle; OC, obturator canal; OIM, obturator internus muscle; OV, obturator vessels; SG, superior gluteal vessels; PVM, pubovisceral muscle; FA, fascial arch (=arcus tendinous fascia pelvis); R, rectum; U, urethra; V, vagina; EAS, external anal sphincter; ACR: anococcygeal raphe. From Halban & Tandler, 1907 [6]

Fig 2.. Comparison between normal pelvic support (left) and prolapse with failed hiatal closure (right) in lithotomy view

Top row: UGH as seen in clinical exam. Bottom row: Lithotomy view of UGH and its relationship to perineal membrane and perineal body in Level III of pelvic support in cadaver dissection. Note close relationship between the perineal membrane and hiatal opening and the significant distortion with prolapse. Lack of information about the role of the perineal membrane in hiatal closure and prolapse is an important knowledge gap. UGH, urogenital hiatus; EAS, external anal sphincter; LA, levator ani muscle; PB, perineal body Bottom row from Halban & Tandler, 1907 [6]

Fig 3.. Comparison between normal pelvic support (left) and prolapse with failed hiatal closure (right) in mid-sagittal view

Comparisons shown after removal of upper pelvic organs. Urogenital hiatus shown as solid line and levator hiatus shown as dotted line. From Halban & Tandler, 1907 [6]

Fig 4.. Schematic view of levator ani muscles, UGH, and LH

a) View of levator ani muscles from below after the vulvar structure and perineal membrane have been removed. Pubovisceral (PVM) and puborectal (PRM) muscles forms the sling around UGH and LH, respectively. PVM includes three parts: pubovaginal muscle (PVaM), puboperineal muscle (PPM), and puboanal muscle (PAM). b) Diagrammatic illustration of muscle loops showing muscle fiber directions for the PVM and PRM relevant to the UGH and LH (green). c) Horizontal and vertical components of the pubovisceral muscle (PVM) and puborectal muscles (PRM) lines of action in the sagittal plane in a standing posture. The thick arrows show the average direction of the lines of action of the pubovisceral and puborectal muscles relative to the horizontal for a theoretical 1 N force. Thin lines indicate how much of that force acts to “close” and “lift” each hiatus. Note: Vectors are shown larger than the background anatomy to avoid an overlap in the display. LH, levator hiatus; UGH, urogenital hiatus Modified from Kearney, 2004 [10] and Betschart, 2014 [11]. ©DeLancey

Fig 5.. Parity and pelvic floor disorders affecting hiatus size based on values for LH AP diameter and area measured by transperineal ultrasound reported in the literature

Dots represent the means of individual studies listed in Tables S1, S9, S10, and S11. Squares represent weighted means based on the studies shown as dots. Standard deviations bars represent the weighted values. LH, levator hiatus; AP, anterior-posterior; R, rest; V, Valsalva; K, Kegel; SUI, stress urinary incontinence; Nullip., nullipara.

Fig 6.. Pregnancy and postpartum hiatal size

Plots of LH size in nullipara along with changes in LH during pregnancy and after birth. Note the generally lower values than in Fig 4. Dots represent the means of individual studies listed in Tables S1-S7. Data that come from a single study are linked by light dotted lines. Squares represent weighted means based on the studies shown as dots. In postpartum columns, filled dots/squares are data for vaginal delivery and open dots/squares are data for cesarean section. Error bars represent weighted standard deviation. LH, levator hiatus; R, rest; V, Valsalva; K, Kegel

Fig 7.. LH, UGH measurements and levator shape

a) Perineal body (Pb), levator plate (LP), levator area (LA), sacrococcygeal inferior-pubic point (SCIPP) line in mid-sagittal view b) 3D view of levator bowl volume (LBV) LH, levator hiatus; UGH, urogenital hiatus Modified from Nandikanti, 2019 [110] and Cheng, 2022 [113]