OBSTETRIC
LACERATIONS II—FIBROMUSCULAR SUPPORT
The most common cause of direct injury to the
vagina is childbirth. Before 1900, when most babies were delivered at home,
these injuries were more frequent. Regardless of refinements in obstetric
management and surgical technique, such accidents, both minor and major,
continue to occur. A large number of variables in a delivery may account for
this, including precipitous labor with sudden expulsion of the head, abnormal
presentation or progress necessitating operative delivery, the large size of
the baby, unusually friable maternal tissues, or an exaggerated lithotomy
position. Vaginal lacerations are more common and more extensive in nulliparous
women in whom the musculature of the birth canal and perineum has not
previously been stretched.
In the cases illustrated, the infant’s head has extended too soon, resulting in a near brow presentation, with increase in the diameter that must pass between the leaves of the pelvic sling at this level. The pressure thus exerted on the vaginal tube and its muscular supports has spread in several directions, but especially posteriorly toward the anus. The superficial muscles of the perineum, including the transverse perineal muscles, the upper margin of the external sphincter ani, and the more superficial fibers of the pubococcygei have been ruptured to form a gaping wound. Some pressure has also been disseminated laterally, tearing the bulbocavernosi and shredding the thin inferior fascia of the urogenital diaphragm. Both urinary and fecal incontinence may result from such an injury. Infrequently, such lacerations are also associated with rectovaginal fistula formation, especially when damage to or frank laceration of the rectal mucosa goes unrecognized and unrepaired.
Because the vagina passes
downward and forward in the interlevator cleft connected by musculofascial
extensions to the pubococcygeus muscles on either side, downward traction on an
infant’s head impeded in mid- vagina may easily tear these connections as well
as the interdigitating muscle fibers between the vagina and rectum. The vagina
is completely separated from the rectum above the level of the external
sphincter ani, and the separation continues laterally without damaging the
major divisions of the pubococcygei. This injury occurs at about the level of
the ischial spines and may be caused by an attempted forceps extraction.
A more severe laceration
at approximately the same level, in addition to separating the pillars of the
pubococcygei by rupturing their attachments to the lateral and posterior
vagina, may tear the posterior puborectalis components, which give the
principal support to the rectum and pelvic floor. The postpartum clinical effect
of this is the development of a rectocele.
An aberrant application
of forceps may cause a deep tear in the pubococcygeus muscle close to its
origin on the inner surface of the superior pubic ramus. Damage of this type is
difficult to recognize or repair at the time of delivery, and serious hemorrhage
or hematoma formation may
ensue. The tear often extends downward to separate the right lateral and
posterior vagina from its supports and from the anterior rectal wall, with loss
of almost an entire wing of the pelvic diaphragm. In the months following
delivery, this may lead to varying degrees of prolapse of the pelvic viscera.
When forceps delivery was
more commonly employed, rare cases of uterine rupture occurred during the
process of placing the forceps blades or during forceps rotation. When forceps are used, and
vaginal bleeding persists, the possibility of a lower uterine tear should be
considered and evaluated by manual uterine exploration.
As with all surgical procedures, clear visualization, meticulous hemostasis, careful tissue handling, and tension-free, anatomically correct reapproximation of any tissues damaged are most likely to achieve a satisfactory outcome.
