The suspensory mechanism of the uterus

Abstract

At rest the uterovaginal tube presents three angles in the sagittal plane: anteflexion, anteversion and the vaginal cap. The most important, from the functional point of view, is the angle of anteversion because it places the uterus perpendicularly in relation to the vagina. This arrangement may be explained by the erect posture of the human being and commences with the toddler as she begins to stand on her feet. The uterus is tethered on each side to the pelvic wall by a bulky neurovascular pedicle composed of uterine and vaginal vessies, the hypogastric plexus and connective tissue in continuity with that of the retroperitoneal space. This pedicle, in passive fashion, maintains the position and direction of the uterus and thanks to its elasticity allows it to mould itself to the variations in volume of the bladder and rectum and take up its normal position once these organs are emptied. The histological structure of this pedicle cannot account for its effectiveness as a suspensory ligament. Support for the uterus in fact derives from the posterior part of the levator muscles of the anus. At rest the uterus lies behind the urogenital fissure. During effort it gains support by the intermediary of the rectum on the posterior part of the anal elevators and the anococcygeal ligament; it thus closes off the pouch of Douglas. The vaginal orifice, which represents a weakness in the muscular diaphragm of the pelvis, is closed during effort by abutment of the anterosuperior wall of the vagina onto the posteroinferior wall. The vagina, almost in the horizontal position, traverses the muscular diaphragm of the pelvis obliquely from above downwards and is thus situated almost perpendicular to the forces of rectal emptying. Contraction of the muscular diaphragm of the pelvis, on account of its bony attachments being diametically opposed, does not close off the urogenital fissure which in the living subject lies very anteriorly in a subpubic position. Contraction results in the anal levators becoming horizontal and displacing the pelvic viscera upwards.