URETHRAL (AND ANTERIOR VAGINAL WALL) SUPPORT SYSTEM

(Fig. 3.8 Schematic view of the levator ani muscles from
below after the vulvar structures and perineal membrane
have been removed showing the arcus tendineus levator ani
(ATLA); external anal sphincter (EAS); puboanal muscle
(PAM); perineal body (PB) uniting the two ends of the
puboperineal muscle (PPM); iliococcygeal muscle (ICM);
puborectal muscle (PRM). Note that the urethra and vagina
have been transected just above the hymenal ring.)


(Fig. 3.9 The levator ani muscle seen from above looking
over the sacral promontory (SAC) showing the pubovaginal
muscle (PVM). The urethra, vagina, and rectum have been
transected just above the pelvic fl oor. PAM, puboanal
muscle; ATLA, arcus tendineus levator ani; ICM,
iliococcygeal muscle. (The internal obturator muscles have
been removed to clarify levator muscle origins.) (From
Kearney et al 2004, with permission of Elsevier North)


Support of the urethra and vesical neck is determined
by the endopelvic fascia of the anterior vaginal wall
through their fascial connections to the arcus tendineus
fascia pelvis and connection to the medial portion of the
levator ani muscle.

It is our working hypothesis that both urethral constriction
and urethral support contribute to continence.
Active constriction of the urethral sphincter maintains
urine in the bladder at rest. During increases in abdominal
pressure, the vesical neck and urethra are compressed
to a closed position when the raised abdominal
pressure surrounding much of the urethra exceeds the
fluid pressure within the urethral lumen.

The stiffness of the supportive layer under the vesical
neck provides a backstop against which abdominal
pressure compresses the urethra. This anatomic division
mirrors the two aspects of pelvic floor function relevant
to SUI: urethral closure pressure at rest and the increase
in urethral closure caused by the effect of abdominal
pressure.

Support of the urethra and distal vaginal wall are
inextricably linked. For much of its length, the urethra
is fused with the vaginal wall, and the structures that
determine urethral position and distal anterior vaginal
wall position are the same.

The anterior vaginal wall and urethral support
system consists of all structures extrinsic to the urethra
that provide a supportive layer on which the proximal
urethra and midurethra rest. The major
components of this supportive structure are the vaginal
wall, the endopelvic fascia, the arcus tendineus fasciae
pelvis, and the levator ani muscles.

The endopelvic fascia is a dense, fibrous connective
tissue layer that surrounds the vagina and attaches it to
each arcus tendineus fascia pelvis laterally. Each arcus
tendineus fascia pelvis in turn is attached to the pubic
bone ventrally and to the ischial spine dorsally.

The arcus tendineus fasciae pelvis are tensile structures
located bilaterally on either side of the urethra and
vagina. They act like the catenary-shaped cables of a
suspension bridge and provide the support needed to
suspend the urethra on the anterior vaginal wall.
Although it is well defined as a fibrous band near its
origin at the pubic bone, the arcus tendineus fascia
pelvis becomes a broad aponeurotic structure as it
passes dorsally to insert into the ischial spine. It therefore
appears as a sheet of fascia as it fuses with the
endopelvic fascia, where it merges with the levator ani
muscles.

The levator ani muscles also play a critical role in supporting
the pelvic organs (Berglas & Rubin 1953, Halban
& Tandler 1907, Porges et al 1960). Not only has evidence
of this been seen in magnetic resonance scans
(Kirschner-Hermanns et al 1993, Tunn et al 1998) but
histological evidence of muscle damage has been found
(Koelbl et al 1998) and linked to operative failure (Hanzal
et al 1993).

There are three basic regions of the levator ani muscle
(Kearney et al 2004) (Figs 3.8 and 3.9):
• the fi rst region is the iliococcygeal portion, which
forms a relatively fl at, horizontal shelf spanning
the potential gap from one pelvic sidewall to the
other;
• the second portion is the pubovisceral muscle, which
arises from the pubic bone on either side and attaches
to the walls of the pelvic organs and perineal body;

• the third region, the puborectal muscle, forms a sling
around and behind the rectum just cephalad to the
external anal sphincter.

The connective tissue covering on both superior and
inferior surfaces are called the superior and inferior
fasciae of the levator ani. When these muscles and their
associated fasciae are considered together, the combined
structures make up the pelvic diaphragm.

The opening within the levator ani muscle through
which the urethra and vagina pass (and through which
prolapse occurs), is called the urogenital hiatus of the
levator ani. The rectum also passes through this opening,
but because the levator ani muscle attaches directly to
the anus it is not included in the name of the hiatus. The
hiatus, therefore, is supported ventrally (anteriorly) by
the pubic bones and the levator ani muscles, and dorsally
(posteriorly) by the perineal body and external
anal sphincter.

The normal baseline activity of the levator ani muscle
keeps the urogenital hiatus closed by compressing the
vagina, urethra and rectum against the pubic bone, the
pelvic fl oor and organs in a cephalic direction (Taverner
1959). This constant activity of the levator ani muscle is
analogous to that in the postural muscles of the spine.
This continuous contraction is also similar to the
Urethral (and anterior vaginal wall) support system
Fig. 3.8 Schematic view of the levator ani muscles from
below after the vulvar structures and perineal membrane
have been removed showing the arcus tendineus levator ani
(ATLA); external anal sphincter (EAS); puboanal muscle
(PAM); perineal body (PB) uniting the two ends of the
puboperineal muscle (PPM); iliococcygeal muscle (ICM);
puborectal muscle (PRM). Note that the urethra and vagina
have been transected just above the hymenal ring.
(© DeLancey 2003.)
Fig. 3.9

continuous activity of the external anal sphincter muscle,
and closes the lumen of the vagina in a manner similar
to that by which the anal sphincter closes the anus. This
constant action eliminates any opening within the pelvic
fl oor through which prolapse could occur.

A maximal voluntary contraction of the levator ani
muscles causes the pubovisceral muscles and the puborectalis
muscles to further compress the mid-urethra,
distal vagina and rectum against the pubic bone distally
and against abdominal hydrostatic pressure more
proximally. It is this compressive force and pressure
that one feels if one palpates a pelvic fl oor muscle
contraction intravaginally. Contraction of the bulbocavernosus
and the ventral fi bres of the iliococcygeus
will only marginally augment this compression
force developed by the pubovisceral and puborectalis
muscles because the former develops little force and the
latter is located too far dorsally to have much effect
intravaginally.

Finally, maximal contraction of the mid and dorsal
iliococcygeus muscles elevates the central region of the
posterior pelvic floor, but likely contributes little to a
vaginal measurement of levator strength or pressure
because they do not act circumvaginally.
Interactions between the pelvic floor muscles
and the endopelvic fasciae

The levator ani muscles play an important role in protecting
the pelvic connective tissues from excess load.
Any connective tissue within the body may be stretched
by subjecting it to a tensile force. Skin expanders used
in plastic surgery stretch the dense and resistant dermis
to extraordinary degrees, and flexibility exercises practiced
by dancers and athletes elongate leg ligaments.
Both these observations underscore the adaptive nature
of connective tissue when subjected to repeated tension
over time.

If the ligaments and fasciae within the pelvis were
subjected to continuous stress imposed on the pelvic
fl oor by the great force of abdominal pressure, they
would stretch. This stretching does not occur because
the constant tonic activity of the pelvic fl oor muscles
(Parks et al 1962) closes the urogenital hiatus and carries
the weight of the abdominal and pelvic organs, preventing
constant strain on the ligaments and fasciae within the
pelvis.
The interaction between the pelvic floor muscles and
the supportive ligaments is critical to pelvic organ
support. As long as the levator ani muscles function to
properly maintain closure of the genital hiatus, the
ligaments and fascial structures supporting the pelvic
organs are under minimal tension. The fasciae simply act
to stabilize the organs in their position above the levator
ani muscles.

When the pelvic floor muscles relax or are damaged,
the pelvic floor opens and the vagina lies between the
zones of high abdominal pressure and low atmospheric
pressure outside the body. In this situation it must be
held in place by the suspensory ligaments. Although the
ligaments can sustain these loads for short periods of
time, if the pelvic floor muscles do not close the pelvic
floor then the connective tissue will eventually fail,
resulting in pelvic organ prolapse.

The support of the uterus has been likened to a ship
in its berth floating on the water attached by ropes on
either side to a dock (Paramore 1918). The ship is analogous
to the uterus, the ropes to the ligaments, and the
water to the supportive layer formed by the pelvic floor
muscles. The ropes function to hold the ship (uterus) in
the center of its berth as it rests on the water (pelvic floor
muscles). If, however, the water level falls far enough
that the ropes are required to hold the ship without the
supporting water, the ropes would break.

The analogous situation in the pelvic floor involves
the pelvic floor muscles supporting the uterus and
vagina, which are stabilized in position by the ligaments
and fasciae. Once the pelvic floor musculature becomes
damaged and no longer holds the organs in place, the
supportive connective tissue is placed under stretch
until it fails.

The attachment of the levator ani muscles into the
perineal body is important and damage to this part of
the levator ani muscle during delivery is one of the
irreparable injuries to pelvic floor. Recent magnetic resonance
imaging (MRI) has vividly depicted these defects
and it has been shown that up to 20% of primiparous
women have a visible defect in the levator ani muscle
on MRI.

It is likely that this muscular damage is an important
factor associated with recurrence of pelvic organ prolapse
after initial surgical repair. Moreover, these defects
were found to occur more frequently in those individuals
complaining of SUI. An individual
with muscles that do not function properly has
a problem that is not surgically correctable.


Support of the urethra and vesical neck is determined
by the endopelvic fascia of the anterior vaginal wall
through their fascial connections to the arcus tendineus
fascia pelvis and connection to the medial portion of the
levator ani muscle.
It is our working hypothesis that both urethral constriction
and urethral support contribute to continence.
Active constriction of the urethral sphincter maintains
urine in the bladder at rest. During increases in abdominal
pressure, the vesical neck and urethra are compressed
to a closed position when the raised abdominal
pressure surrounding much of the urethra exceeds the
fluid pressure within the urethral lumen.

The stiffness of the supportive layer under the vesical
neck provides a backstop against which abdominal
pressure compresses the urethra. This anatomic division
mirrors the two aspects of pelvic floor function relevant
to SUI: urethral closure pressure at rest and the increase
in urethral closure caused by the effect of abdominal
pressure.

Support of the urethra and distal vaginal wall are
inextricably linked. For much of its length, the urethra
is fused with the vaginal wall, and the structures that
determine urethral position and distal anterior vaginal
wall position are the same.

The anterior vaginal wall and urethral support
system consists of all structures extrinsic to the urethra
that provide a supportive layer on which the proximal
urethra and midurethra rest. The major
components of this supportive structure are the vaginal
wall, the endopelvic fascia, the arcus tendineus fasciae
pelvis, and the levator ani muscles.

The endopelvic fascia is a dense, fibrous connective
tissue layer that surrounds the vagina and attaches it to
each arcus tendineus fascia pelvis laterally. Each arcus
tendineus fascia pelvis in turn is attached to the pubic
bone ventrally and to the ischial spine dorsally.

The arcus tendineus fasciae pelvis are tensile structures
located bilaterally on either side of the urethra and
vagina. They act like the catenary-shaped cables of a
suspension bridge and provide the support needed to
suspend the urethra on the anterior vaginal wall.
Although it is well defined as a fibrous band near its
origin at the pubic bone, the arcus tendineus fascia
pelvis becomes a broad aponeurotic structure as it
passes dorsally to insert into the ischial spine. It therefore
appears as a sheet of fascia as it fuses with the
endopelvic fascia, where it merges with the levator ani
muscles