Innervation of the Female Levator Ani Muscle and Consequences in Pelvic Floor Dysfunctions

Abstract

IntroductionThe Levator Ani Muscle (LAM) and the Levator Ani Nerve (LAN) are distended and traumatized during pregnancy and vaginal delivery. Both mechanisms may sustainably impair the pelvis statics but the topography and functions of the nerve supply to the LAM remain anatomically controversial.ObjectiveTo characterize the nature and function of the LAM nerve pathways and to perform a comprehensive 3D reconstruction of the female pelvic innervation.MethodsThe Computer‐Assisted Anatomical dissection (CAAD) protocol was applied to pelvic blocks procured in 6 female human fetuses, in accordance with the National Biomedicine Agency. Specimens were serially sectioned and immunostained for: overall (S100), somatic (PMP22), adrenergic (TH), cholinergic (VaCHT) and nitrergic (nNOS) nerve fibers and for: smooth (smooth actin) and striated (myogenin) muscle fibers. Slides were digitized for 3D reconstructions on WinSurf®. A pelvic sample of an additional fetus was examined under electronic microscopy to analyze the ultrastructure of the LAM.ResultsThree main nerve pathways to the LAM were observed: the levator ani nerve (LAN), the pudendal nerve (PuN), the inferior hypogastric plexus (IHP). The PuN was both somatic and autonomic, located below the LAM (‘infralevator pathway’) and supplying innervation to the inferior aspect of the LAM. The LAN was solely somatic, located above the LAM (‘supralevator pathway’) and supplying innervation to the superior aspect of the LAM. The IHP nerve fibers were solely autonomic, located in between the LAM and the pelvic organs (‘endolevator pathway’) and supplying innervation to the medial portion of the LAM. Smooth muscle areas were identified with labelings and electronic microscopy: they 1) were located in the puboanal sling of the LAM 2) were bulging between rectum and vagina 3) were intermingled to the anococcygeal raphe 4) were innervated by the IHP and the PuN pathways.ConclusionHaving at once striated and smooth muscle fibers and being co‐innervated by the somatic and autonomic systems, the LAM represents a crucial anatomical structure involved in the pelvic floor function and its rehabilitation.Support or Funding Informationnone