Trudy Van Houten
All figures in this chapter are the copyright of Dr Trudy Van Houten, Harvard Medical School and Department of Radiology, Brigham and Women’s Hospital, Boston, MA, USA
The term “pelvic organ prolapse” encompasses a spectrum of debilitating medical conditions. Weakening or failure of the pelvic organ support system can lead to uterine prolapse, including emergence of the cervix through the labia minora; protrusion of portions of the urinary bladder, urethra, small intestine, or rectum through the vaginal wall; difficulty in evacuating the bladder or rectum; and, conversely, difficulty in maintaining urinary or fecal continence. Recent studies of the impact of these conditions on sexual function have adopted widely differing methodologies and have presented conflicting results. It seems intuitively certain, however, that for many patients, the discomfort, pain, and embarrassment associated with pelvic floor disorders significantly diminishes self-esteem and sexual enjoyment, if not sexual function.
Pelvic organ prolapse is a major health concern for older women, particularly postmenopausal women, but younger women may also be affected. Nygaard and colleagues concluded that some degree of prolapse is nearly ubiquitous in older women.1 Tarnay and Bhatia estimate that urinary incontinence alone affects 13 million women in the USA.2 Olsen and colleagues calculated an 11.1% lifetime risk of undergoing a single operation for pelvic organ prolapse and urinary incontinence.3 The annual direct cost of urinary incontinence in the USA (in 1995 dollars) was estimated as $16.3 billion, including $12.4 billion (76%) for women and $3.8 billion (24%)for men.4 The actual incidence of pelvic organ prolapse may also significantly exceed the reported incidence, and the number of women affected by pelvic floor disorders is also likely to increase sharply as longevity is extended and the population of aging women increases. The single greatest risk factor for pelvic organ prolapse is vaginal birth. Mant and colleagues found that a woman was four times more likely to develop prolapse after the birth of her first child, and 11 times more likely to develop prolapse with four or more deliveries.5
The effectiveness of surgical treatment for pelvic organ prolapse and urinary and fecal incontinence is difficult to evaluate but overall is discouraging. Olsen and colleagues estimate that 29% of women undergoing surgery for pelvic organ prolapse will require at least one reoperation, and that the time intervals between repeat procedures decreases with each subsequent reoperation.3 In a retrospective study, Whiteside and colleagues found that 58% of women undergoing vaginal prolapse and incontinence surgery had recurrent prolapse at 1-year followup.6 This finding suggests that recurrence rates for pelvic organ prolapse may be even higher than reoperation rates. Cundiff recently stated that the number of techniques currently advocated for treatment of rectocele is “another suggestion of less than optimal effectiveness for surgical intervention”.7 Tarnay and Bhatia identified 130 operative procedures for the treatment of female urinary stress incontinence, concluding that it is “not surprising that many of the procedures have not had longterm success”.2
Recent magnetic resonance imaging (MRI) studies and three-dimensional modeling techniques provide a powerful new method for analyzing the anatomy of the pelvic floorC13 However, profound difficulties with traditional descriptions of pelvic floor anatomy, the lack of a precise standardized terminology for describing the components of the pelvic organ support system, and the exuberant proliferation of unexplained synonyms in the literature make it difficult to compare, or even interpret, the findings from different imaging studies, surgical series, and laboratory dissections. It is even more challenging to assemble the rapidly accumulating data into a reliable and consistent body of knowledge useful for understanding the anatomic basis of pelvic organ prolapse, and effectively diagnosing and treating this condition.
The present discussion is a critical review of currently available information on the anatomy of the pelvic organ support system.
Normal anatomy of the pelvic organ support system
Maintaining the pelvic organs in their normal anatomic positions requires continual resistance to the forces of gravity and to increases in intra-abdominal pressure that occur during coughing, sneezing, urination, defecation, pregnancy, and delivery. The structures supporting the pelvic organs comprise an integrated system consisting of four basic components (Fig. 4.4.1).
1. Pelvic bones, joints, and interosseous ligaments. The bones of the pelvis, the joints uniting the pelvic bones, and the sturdy interosseous ligaments reinforcing the pelvic joints provide a rigid articulated framework surrounding the pelvic organs. The pelvic bones, joints, and interosseous ligaments also provide attachment sites for the midline connective tissue structures of the pelvic outlet, and for the muscles of the pelvic walls, pelvic floor, and perineum.
Figure 4.4.1. Components of the pelvic organ support system.
1 Pelvic bones, joints, and interosseous ligaments; 2 Midline connective tissue structures of the pelvic outlet; 3 Pelvic muscles and investing pelvic fascia; 4 Visceral pelvic fascia and visceral fascial ligaments.
2. Midline connective tissue structures of the pelvic outlet. The perineal membrane, perineal body, and anococcygeal ligament form a series of dense connective tissue structures bridging the pelvic outlet in the anteroposterior midline. The midline connective tissue structures resist downward movement of the pelvic contents and provide attachment sites for the muscles of the pelvic floor and perineum. Fibers of the muscles attaching to the midline connective tissue structures become interwoven with one another, and this web of muscle fibers reinforces the midline connective tissue structures.
3. Pelvic muscles and investing pelvic fascia. The muscles of the pelvic walls close apertures between the pelvic bones and ligaments, but the muscles of the pelvic floor are the active supports of the pelvic contents. The resting tone of the pelvic floor muscles supports the pelvic contents and resists their downward movement; contraction of the pelvic floor muscles helps increase intraabdominal pressure during Valsalva maneuvers. The medial muscles of the pelvic floor act in concert with the deep perineal muscles as the continence mechanisms of the urethra and vagina. The dense investing pelvic fascia invests the surfaces of the muscles of the pelvic walls and floor and blends with the periosteum of the pelvic bones. The investing pelvic fascia covering the pelvic walls condenses to form a sturdy tendinous arch that provides attachment for the muscles of the pelvic wall. The investing pelvic fascia covering the muscles of the pelvic floor condenses to form another sturdy tendinous arch that provides attachment for the visceral pelvic fascia anchoring the pelvic organs to the pelvic walls and floor. The presacral fascia covering the sacrum also anchors elements of the pelvic floor and the visceral pelvic fascia.
4. Visceral pelvic fascia and visceral fascial ligaments. The visceral pelvic fascia is a three-dimensional connective tissue layer, occupying the spaces between the pelvic organs, the investing pelvic fascia, and the peritoneum lining the abdominopelvic cavity. The visceral pelvic fascia forms a complex connective tissue scaffold between the pelvic organs and the pelvic walls, sacrum, and midline connective tissue structures of the pelvic outlet. The visceral pelvic fascia is highly variable in composition. In some areas, it is relatively amorphous; in other areas, it condenses into demonstrable ligaments. The rectovaginal septum has a different embryonic origin, but it forms an important part of the visceral fascial scaffold, reinforcing the posterior vaginal wall and tying the perineal body to the scaffold and to the pelvic walls and upper part of the pelvic floor.
As an integrated system, the components of the pelvic organ support system normally work together to maintain the horizontal and vertical position of the pelvic organs and to maintain alignment of the continence mechanisms. Strain resulting from defects in one component of the pelvic organ support system can initiate defects in other components of the system.
Pelvic bones, joints, and interosseous ligaments
The bony pelvis serves three primary functions: it acts as a relatively rigid cage supporting the abdominal and pelvic organs; it transmits body weight to the lower limbs when standing; and it provides attachment for the ligaments, muscles, and fascia of the trunk wall, back, pelvic floor, perineum, and lower limbs.
The bones of the pelvis form a sturdy articulated ring with the paired os coxae (innominate bones) anterolaterally and the sacrum and coccyx posteriorly. Each os coxae itself consists of three bones, the ilium, ischium, and pubis, which meet at the acetabulum (socket) of the hip joint (Fig. 4.4.2). Ossification of the epiphyses between the three bones is normally completed by age 22. Some important anatomic landmarks on the bony pelvis are shown in Fig. 4.4.3. The ischial spine is a particularly important landmark, since it provides attachment for many of the muscles and connective tissue structures of the pelvic organ support system.
The ilium consists of a broad flat ala superiorly, which articulates posteriorly with the sacrum, and a body inferiorly which fuses with the ischium and pubis (Fig. 4.4.3). The ilium thickens at the junction between the ala and body as an adaptation for transmitting weight from the sacroiliac joint across the ilium to the acetabulum of the hip joint. This thickened buttress is marked by the arcuate line visible on radiographs of the pelvis. The superior margin of the ala widens to form the iliac crest. The gluteal muscles of the lower limb attach to the external surface of the ala. The pelvic surface of the ala forms a gentle concavity, the iliac fossa, which provides attachment for the iliacus muscle of the lower limb.
Figure 4.4.2. Pelvic bones; lateral oblique view with left os coxae distracted. 1 Sacrum; 2 Coccyx; 3 Ilium; 4 Pubis; 5 Ischium.
The ilium, ischium, and pubis comprise the os coxae (innominate bone).
Figure 4.4.3. Important landmarks of the pelvic bones; lateral oblique view with left os coxae distracted.
1 Anterior superior iliac spine; 2 Iliac fossa; 3 Arcuate line; 4 Iliac crest; 5 Ischial spine; 6 Greater sciatic notch; 7 Lesser sciatic notch; 8 Pubic tubercle; 9 Symphyseal surface of the pubic bone covered with hyaline articular cartilage; 10 Ischiopubic ramus; 11 Obturator foramen; 12 Acetabulum; 13 Ischial tuberosity; 14 Anterior sacral foramina.
The ischium consists of a robust body and an ischial ramus. The ischial spine projects from the posterior margin of the ischial body, separating the greater sciatic notch superiorly from the lesser sciatic notch inferiorly (Fig. 4.4.3). The body of the ischium is very robust where it forms the prominent ischial tuberosity. The ischial tuberosities support the body weight when seated, provide attachment for the hamstring muscles of the lower limb, and provide the posterior attachment for structures in the perineum.
The pubis consists of a body and superior and inferior pubic rami. The bodies of the left and right pubic bones articulate in the anterior midline at their symphyseal surfaces to form the pubic symphysis (Fig. 4.4.3). The superior ramus runs posteriorly to fuse with the bodies of the ilium and ischium at the acetabulum; the inferior ramus runs posteroinferiorly to fuse with the ischial ramus, forming the ischiopubic ramus. The superior and inferior pubic rami, and the body of the ischium, enclose the obturator foramen. The pubic arch is framed by the diverging ischiopubic rami.
The sacrum normally consists of five sacral vertebrae fused in a curve (Fig. 4.4.3). The pelvic surface of the sacrum is concave; the external surface is convex and bears sacral crests. Laterally, the upper portion of the sacrum widens to meet the ilium at the sacroiliac joint. The meninges and the roots of the sacral spinal nerves run within the sacral canal, which opens inferiorly at the sacral hiatus. The anterior and posterior rami of the spinal nerves leave the sacral canal through the anterior and posterior sacral foramina, respectively. The coccyx consists of a series of three to five small vertebrae joined to the apex of the sacrum.
Pelvic joints and ligaments
The pubic symphysis is a midline fibrocartilaginous joint that permits only slight angulation and rotation. The symphysis is reinforced superiorly by the superior pubic ligament and inferiorly by the inferior pubic (arcuate) ligament (Fig. 4.4.4).
The entire weight of the trunk, head, neck, and upper limbs is transmitted to the pelvis and lower limbs through the vertebral column and sacrum. The anterior and posterior longitudinal ligaments reinforce the vertebral column and intervertebral joints, including the joint between the fifth lumbar vertebra and the sacrum. Anterior sacrococcygeal ligaments stabilize the sacrococcygeal and intercoccygeal joints. From the sacrum, body weight is transmitted to the ilium across the broad articular surfaces of the sacroiliac joints. Although they are technically synovial joints, the complexly reciprocal articular surfaces of the sacroiliac joints normally permit only slight gliding. The sacroiliac joints may become fibrous, or even ossify, in older individuals. Each sacroiliac joint is reinforced by robust anterior and posterior sacroiliac ligaments, and by the interosseous sacroiliac ligament superiorly.
Figure 4.4.4. Pelvic joints and ligaments; lateral oblique view with left os coxae distracted.
1 Superior pubic ligament; 2 Inferior pubic (arcuate) ligament; 3 Anterior longitudinal ligament; 4 Posterior longitudinal ligament; 5 Anterior sacrococcygeal ligament; 6 Auricular surface of sacrum at sacroiliac joint; 7 Sacrospinous ligament; 8 Sacrotuberous ligament; 9 Obturator membrane.
Each sacroiliac joint is further stabilized by two substantial, dense connective tissue ligaments that anchor the inferior part of the sacrum to the ischium (Fig. 4.4.4). The sacrospinous ligament extends from the sacrum to the ischial spine, separating the greater sciatic notch from the lesser sciatic notch, and completing the greater sciatic notch to form the greater sciatic foramen. The sacrotuberous ligament runs external to the sacrospinous ligament and extends from the sacrum to the ischial tuberosity. The sacrospinous and sacrotuberous ligaments together complete the lesser sciatic notch to form the lesser sciatic foramen. Each obturator membrane is a thin plate of dense connective tissue anchored to the margins of the obturator foramen and closing the foramen except for the small obturator canal anterosuperiorly (Fig. 4.4.4).
The pelvic joints and ligaments relax during the later stages of pregnancy, permitting greater rotation and possible sacroiliac joint subluxation.14 Although the position of the sacrum may alter only slightly after sacroiliac rotation or subluxation, any change could conceivably increase strain on the other structures comprising the pelvic floor support system, and this would be particularly important if other components of the system had been weakened or damaged during childbirth.
In normal standing position, the ischiopubic rami are dependent and the pelvic outlet is obliquely posterior rather than directly inferior. A vertical plane passing through the anterior superior iliac spines intersects the pubic tubercles, and a horizontal plane passing through the superior surface of the pubic symphysis intersects the ischial spines and apex of the sacrum.
Even with its joints and ligaments in place, the articulated bony pelvis forms a barred cage rather than a bowl surrounding the abdominopelvic viscera. The muscles, fasciae, and connective tissue of the abdominal walls, pelvic walls, and pelvic floor convert the pelvis from a cage to a container for the abdominopelvic viscera.
The muscles and fasciae of the abdominal walls attach along the superior surfaces of the pubis and the alae of the ilium. The flared alae and the superior part of the sacrum form the “greater pelvis” or “false pelvis”, which surrounds the inferior extent of the abdominal cavity. The pelvic inlet (pelvic brim) is an irregularly round or oval opening bounded by the pubis anteriorly, the arcuate line of the ilium laterally, and the sacrum posteriorly (Fig. 4.4.5). The pelvic inlet is continuous superiorly with the “greater pelvis” and abdominal cavity.
The pelvic outlet is an irregular, diamond-shaped opening bounded by the ischiopubic rami anteriorly, the ischial tuberosity and sacrotuberous ligament laterally, and the coccyx posteriorly (Fig. 4.4.5). All landmarks of the pelvic outlet are palpable on physical examination. An imaginary line connecting the anterior surfaces of the ischial tuberosities divides the pelvic outlet into two triangles and forms the base for both the urogenital and anal triangles (Fig. 4.4.5). The apex of the urogenital triangle lies anteriorly at the pubic symphysis; the apex of the anal triangle lies posteriorly at the sacrum and coccyx. The planes of the urogenital triangle and anal triangles intersect at an angle. Baragi and colleagues found that the overall area of the pelvic outlet is 5.1% smaller in African-American women than in European-American women,15 a fact which may partially explain the lower incidence of pelvic floor disorders in African-American women.
The pelvic walls include the entire bony pelvis inferior to the arcuate line, and the obturator membranes, sacrotuberous ligaments, and sacrospinous ligaments (Fig. 4.4.5). The muscles of the pelvic wall cover and partially close the obturator foramen, greater sciatic foramen, and lesser sciatic foramen. The pelvic walls form the lateral limits of both the pelvic cavity and the perineum. The paired muscles of the pelvic floor attach laterally along the pelvic walls in a continuous line from the pubis to the sacrum, converge medially around the inferior portions of the pelvic organs, and form an aponeurosis posterior to the rectum. The pelvic cavity (“lesser pelvis” or “true pelvis”) is the anatomic region bounded by the pelvic inlet superiorly, the pelvic walls laterally, and the muscles of the pelvic floor inferiorly (Fig. 4.4.5). The pelvic cavity is occupied by the pelvic viscera and their fascial supports and peritoneal covering, and by the nerves and blood vessels of the pelvic organs and lower limbs. The perineum is the anatomic region bounded by the muscles of the pelvic floor superiorly; the pelvic walls laterally; the coccyx and gluteus maximus muscle posteriorly; and the skin of the vulva, inferior buttocks, and superomedial thighs inferiorly. The perineum is occupied by the urethra, vagina, and anus; the urethral and anal continence mechanisms; the external genitalia; abundant subcutaneous fat filling the ischioanal fossae in the anal triangle; the nerves and blood vessels supplying the perineal structures; and the midline connective tissue structures of the pelvic outlet.
Midline connective tissue structures of the pelvic outlet
Attachment sites for the pelvic muscles include not only the bones and sturdy interosseous ligaments of the pelvis but also the midline connective tissue structures of the pelvic outlet and the thick connective tissue covering the muscles of the pelvic wall (Fig. 4.4.6).
A series of midline connective tissue structures bridges the pelvic outlet from the pubis to the coccyx. The dense fibrous connective tissue of the perineal membrane, perineal body, and anococcygeal ligament (anococcygeal body) support structures superior to the pelvic outlet and provide a series of stable attachment sites for the muscles of the pelvic floor, the muscles of the urethral and anal continence mechanisms, the external genitalia, and the muscles of the external genitalia. Fibers from the pelvic and perineal muscles attaching to the midline connective tissue structures become interwoven with one another to form a substantial fibromuscular chain bridging the pelvic outlet. Continuity between the perineal body and the anococcygeal complex is provided by the dense fibrous connective tissue and muscles surrounding the anus.
The perineal membrane (Fig. 4.4.6) is a sheet of dense fibrous connective tissue spanning the interval between the ischiopu- bic rami. Central openings in the perineal membrane allow passage for the terminal portions of the urethra and vagina. Connective tissue attachments between the urethra, vagina, and perineal membrane may enable the perineal membrane to function as a platform supporting the urethra and vagina.
Figure 4.4.5. Pelvic inlet (red line) and pelvic outlet (green line); lateral oblique view with left os coxae distracted. 1 Urogenital triangle anteriorly within pelvic outlet; 2 Anal triangle posteriorly within pelvic outlet.
Figure 4.4.6. Midline connective tissue structures of the pelvic outlet; lateral oblique view with left os coxae distracted. 1 Perineal membrane; 2 Transverse perineal ligament; 3 Perineal body; 4 Anococcygeal ligament.
Inset: 5 Urethra; 6 Vagina; 7 Rectum.
Anterior to the urethral opening, the margin of the perineal membrane thickens to form the transverse perineal ligament (Fig. 4.4.6). The deep dorsal vein of the clitoris passes between the arcuate ligament and the transverse perineal ligament to enter the pelvic cavity. In the midline, the posterior margin of the perineal membrane fuses with the perineal body. The muscles of the urethral continence mechanism attach to the superior surface of the perineal membrane; the external genitalia and the muscles of the external genitalia attach to the inferior surface of the perineal membrane.
The perineal body (Fig. 4.4.6) is a conical node of dense fibroelastic connective tissue and interlacing muscle fibers occupying the approximate center of the perineum. The base of the perineal body lies in the plane of the perineal membrane; the apex extends superiorly for several centimeters. The perineal body is anchored anteriorly to the perineal membrane (and through the perineal membrane to the ischiopubic rami), posteriorly to the muscles and fibrous coat of the anorectum, and superiorly to the rectovaginal fascia. The rectovaginal fascia links the perineal body to the support scaffold formed by the visceral pelvic fascia and to the presacral fascia covering the sacrum. The perineal body provides direct attachment for the puboperineal fibers of the pelvic floor muscles, for the external anal sphincter, and for all perineal muscles except ischiocaver- nosus. All the muscles attaching to the perineal body contribute fibers to an interlacing meshwork that surrounds and reinforces it.
The anococcygeal ligament (anococcygeal body; Fig. 4.4.6) is a fibroelastic structure extending from the external anal sphincter and connective tissue coat of the anorectum to the coccyx and presacral fascia. Superiorly, the anococcygeal ligament lies directly parallel to the median raphe of the iliococcygeus muscle, an important muscle of the pelvic floor. The anococcygeal ligament and ilioccygeal raphe blend at their attachments to the coccyx and anorectum.
The perineal membrane is fixed by its lateral attachments to the ischiopubic rami, but the perineal body and anococcygeal ligament are more mobile, particularly the anococcygeal ligament. Contraction of the pelvic floor muscles causes upward movement of the anococygeal ligament and anus; increases in intra-abdominal pressure cause downward movement of these structures.
Pelvic muscles and investing pelvic fascia
The pelvic muscles include the muscles of the pelvic walls and the muscles of the pelvic floor.
Muscles of the pelvic walls
The muscles of the pelvic wall cover the large apertures framed by the bony struts and ligaments of the pelvic walls - the obturator, and greater sciatic and lesser sciatic foramina (Fig. 4.4.7). Between the pubis and the ischial spine, the dense investing pelvic fascia covering the muscles of the pelvic walls thickens conspicuously to form an attachment site for the muscles of the pelvic floor.
The obturator internus muscle closes both the obturator foramen and the lesser sciatic foramen (Fig. 4.4.7). Obturator internus originates from the pelvic margins of the obturator foramen and the obturator membrane, closely follows the pelvic wall posteriorly, passes through the lesser sciatic foramen, turns sharply, and inserts on the greater trochanter of the femur. Obturator internus functions as a lateral rotator of the lower limb. The nerve to obturator internus (L5, S1) innervates the obturator internus muscle, entering its perineal surface inferior to the pelvic floor. The internal pudendal and obturator vessels provide the vascular supply to obturator internus. The obturator canal, at the anterosuperior border of obturator internus, transmits the obturator nerves and vessels from the pelvic cavity to the muscles and skin of the medial thigh. The obturator nerve (L2-4) supplies obturator externus, but not obturator internus.
Figure 4.4.7. Muscles of the pelvic walls and striated muscles of the urethra and anus; lateral oblique view with left os coxae distracted.
Muscles of the pelvic walls: 1 Obturator internus; 2 Piriformis; 3 Coccygeus; 4 Tendinous arch of levator ani (condensation of investing fascia over the obturator internus muscle).
Striated muscles of the urethra and anus: 5 External urethral sphincter (sphincter urethrae); 6 Compressor urethrae; 7 Sphincter urethrovaginalis; 8 External anal sphincter.
The piriformis muscle closes the greater sciatic foramen (Fig. 4.4.7). Piriformis originates on the pelvic surface of the sacrum by three slips surrounding the second and third anterior sacral foramina, and then passes laterally through the greater sciatic foramen to insert on the greater trochanter of the femur. Like the obturator internus muscle, piriformis functions as a lateral rotator of the lower limb. The nerve to piriformis (L5, S12) enters the pelvic surface of the muscle. The lateral sacral and superior gluteal arteries provide the vascular supply to piriformis.
Many important neurovascular structures leave the pelvic cavity through the greater sciatic foramen, and these structures are vulnerable to injury during pelvic or perineal surgery. Structures leaving the pelvic cavity between piriformis and the muscles of the pelvic floor include the inferior gluteal nerves and vessels, sciatic nerve, posterior cutaneous femoral nerve, nerve to quadratus femoris, nerve to obturator internus, pudendal nerve, and internal pudendal vessels. As they leave the greater sciatic foramen, the last three structures make a sharp turn around the external surface of the ischial spine and enter the perineum inferior to the pelvic floor, and then run anteriorly in a fascial canal formed by the investing pelvic fascia covering the obturator internus muscle. Any of the structures leaving the greater sciatic foramen inferior to piriformis are vulnerable to injury during sacrospinous colpopexy, a surgical procedure in which the vaginal vault is suspended from the sacrospinous ligament.
The pudendal nerve (S2-4) or its branches may also be injured in their perineal course over the obturator internus muscle during procedures using transvaginal or transanal surgical approaches. The inferior rectal branch of the pudendal nerve provides motor innervation to the external anal sphincter and conveys sensation from the anal skin and the inferior portion of the anal canal. The perineal branch of the pudendal nerve provides motor innervation to the urinary continence mechanism and muscles of the external genitalia, and it conveys sensation from the perineum, including the labia, lower portion of the vagina, and clitoris.16 Welgoss and colleagues reported prolonged perineal nerve terminal latencies postoperatively, compared with baseline presurgical measurements, in 11 of 31 women undergoing bilateral sacrospinous ligament vault suspension and bilateral paravaginal cystocele repair.17 In this study, women with perineal neuropathy were more likely to have a suboptimal surgical outcome than women without perineal neuropathy.
Parietal pelvic fascia
The term “fascia” is used in the anatomic and surgical literature to refer to any of a large number of diverse connective tissue structures with very different shapes, locations, tissue properties, and functions. A fascial structure may be a flat sheet or a thick layer; it may be a sturdy conspicuous structure or a collagenous condensation within a loose amorphous agglomeration. Unfortunately, the use of the term “fascia” to describe very disparate structures may seem to imply an unwarranted anatomic or functional similarity.
Three different fascias are found in the pelvis and perineum. The subcutaneous fat (superficial fascia, hypodermis) of the perineum and ischioanal fossa lies directly beneath the dermis of the skin, and consists of a loose network of collagen fibers containing many adipocytes. Anteriorly, the subcutaneous fat forms the bulk of the mons pubis and labia majora. Posteriorly the subcutaneous fat expands, filling the relatively large spaces between the pelvic floor, pelvic walls, anorectum, and skin, and extends anteriorly for a short distance above the perineal membrane. Colles’ fascia is a recognizable condensation of collagen fibers near the internal limit of the subcutaneous fat of the perineum.
The parietal pelvic fascia covering the muscles of the pelvic walls, pelvic floor, and perineum is continuous with the deep investing fascia surrounding all the bones and striated muscles of the body. This dense connective tissue layer fuses with the epimysium covering individual muscles, splits to surround muscle groups, bridges the gaps between muscles, and fuses with the periosteum of bones. All muscles have a covering of deep fascia, including the muscles of the thorax, abdomen, and pelvis. The deep investing fascia covers both the external surfaces of the muscles and the internal surfaces facing the body cavities. Although the deep investing fascia forms a continuous layer, its essential continuity may be obscured by the regional names applied to it. The term “investing pelvic fascia” is used to describe the entire investing deep fascial layer covering the pelvic surfaces of the pelvic walls and floor. Specific terms, such as “obturator internus fascia”, “presacral fascia”, “piriformis fascia”, and “levator ani fascia”, describe regions of this continuous layer, and not separate structures.
The investing pelvic fascia varies greatly in thickness from a thin covering inseparable from the epimysium to robust structures capable of providing secure attachment for muscles or for other connective tissue structures. The investing pelvic fascia covering the obturator internus muscle thickens to form a substantial tendinous arch, the tendinous arch of levator ani (Fig. 4.4.7), which provides a sturdy attachment for the iliococcygeus muscle and part of the pubococcygeus muscle between their bony attachments. Iliococcygeus and pubococcygeus are muscles of the pelvic floor. The deep investing fascia covering iliococcygeus thickens to form another substantial tendinous arch, the tendinous arch of the pelvic fascia (white line) (Fig. 4.4.7), continued anteriorly as the pubovesical ligament. The visceral pelvic fascia supporting the pelvic organs blends laterally with the tendinous arch of the pelvic fascia, which anchors it to the pelvic wall. In the Terminologia Anatomica,18 the term “endopelvic fascia” is listed as a synonym for “pelvic investing fascia”. In the clinical literature, however, the term “endopelvic fascia” is generally used as a synonym for “visceral pelvic fascia.”
The visceral pelvic fascia (endopelvic fascia) filling the spaces between the pelvic organs, pelvic walls, pelvic floor, and the peritoneum lining the abdominopelvic cavity is highly variable in terms of its tissue properties. The visceral pelvic fascia everywhere consists of smooth muscle, collagen fibers, and elastin fibers. In some regions, the collagen fibers and elastin fibers are relatively dispersed, in other regions they form demonstrable ligaments such as the cardinal and uterosacral ligament complex. The visceral pelvic fascia and the visceral fascial ligaments are described more fully in a later section.
Muscles of the pelvic floor
The clinical importance of the muscles of the pelvic floor far exceeds the clarity and accuracy of most descriptions of pelvic floor anatomy. Almost no other region of the body is so commonly described in unhelpful generalizations, confusing and overlapping terminology, and misleading metaphor. These conceptual difficulties are not mere quibbles, but real obstacles to understanding the pelvic organ support system and the role of the pelvic floor muscles within that system.
In most traditional accounts, the pelvic floor muscles are described as the “pelvic diaphragm”, which consists of the coccygeus (ischiococcygeus) and levator ani muscles.18-25 The levator ani muscle is said to consist of the iliococcygeus and pubococcygeus muscles, and pubococcygeus is said to consist of the pubourethralis and puborectalis muscles. Additional small muscles, such as the puboperinealis and puboanalis, may also be included in levator ani. The editors of the 39th British edition of Gray’s Anatomy include ischiococcygeus (coccygeus) in levator ani.26 The terms “pelvic diaphragm” and “levator ani muscle” are currently used more or less interchangeably in the literature with little explanation of how inclusively they are meant to be interpreted.
At every level of generalization, the structures included are nearly always described as “a muscle”, although the paradoxical consequence of this description is that levator ani is a muscle comprised of other muscles, a situation unparalleled in any other region of the body. And, at every level of generalization, the function of the pelvic floor muscle or muscles is described as “supporting the pelvic viscera”. The interesting and clinically important questions, however, are exactly how each of the muscles of the pelvic floor contributes to the support of the pelvic organs, how the failure of one pelvic floor muscle affects the other components of the pelvic organ support system, and how the intact components of the pelvic organ support system may be safely and effectively recruited, or augmented, to compensate for the failed structure. Detailed studies of the functions of the individual muscles of the pelvic floor, rather than studies of the functions of “levator ani” or the “pelvic diaphragm”, are requisite for an adequate understanding of the normal and pathologic anatomy of the pelvic floor and the pelvic organ support system. The first step in addressing the functions of the individual muscles of the pelvic floor is a specific and consistent terminology for referring to them. Difficulties in reconciling the terms and measurement points used by different researchers and clinicians lead to difficulties in interpreting or comparing the results of their research studies or surgical series.
Recent MRI studies have elegantly documented normal pelvic floor anatomy,12-27 identified defects in pelvic wall anatomy,10,11 and compared pelvic wall anatomy in patients with pelvic organ prolapse and normal controls.11,13,14,29 Several studies have attempted to identify imaging markers that can be used to diagnose pelvic floor dysfunction, to assess the severity of pelvic floor dysfunction, and to assist in treatment planning.10,13,14 Singh and colleagues have described four patterns of change in levator ani conformation associated with pelvic floor dysfunction.28
These imaging studies have great potential for enhancing our knowledge of pelvic floor anatomy, and they offer the possibility of more accurate diagnosis and effective treatment of pelvic floor disorders. Their comparability and applicability, however, are limited by persistent difficulties with the terminology used to refer to the muscles of the pelvic floor, by the use of ambiguously defined reference points, and by the use of unexplained terms.
In a recent review, Kearney and colleagues summarized the conflicting terminology used by various authors to describe the levator ani muscle group.19,29 They suggest that although there is widespread disagreement on the terminology applied to the muscles of the pelvic floor, there is basic consensus on the origins and insertions of the muscles themselves. These authors sensibly propose a standardized terminology for the pelvic floor muscles based on their attachment sites. It is worth pointing out, however, that strict application of this principle requires a terminological revision perhaps more radical than the authors intended, requiring elimination of the terms “levator ani”, “ilio- coccygeus”, and “pelvic diaphragm”. Specific muscle names, based on attachments will be used throughout the following discussion.
Consideration of the origins and insertions of the muscles of the pelvic floor presents two initial difficulties for the traditional account. First, the coccygeus (ischiococcygeus) muscle cannot actively support the pelvic viscera. The inconstant muscle fibers of coccygeus (ischiococcygeus) originate on the lateral pelvic surfaces of the fifth sacral vertebra and coccyx, follow the sacrospinous ligament laterally, and insert on the ischial spine (Fig. 4.4.7). In quadrupeds, the sacrospinous ligament is absent, and coccygeus is a robust depressor and lateral flexor of the tail. In humans, the sacrospinous ligament is robust, and the muscle fibers of coccygeus are often few or absent, suggesting that, in humans, coccygeus has lost its active role as a tail muscle and is evolving into a ligament. Regardless of its evolutionary antecedents and robusticity, attachments of coccygeus to the sacrum, coccyx, and ischial spine, and lack of attachment to the pelvic viscera or midline connective tissue structures, would exclude coccygeus from any role in supporting the pelvic organs. For this reason, coccygeus is probably better included among the muscles of the pelvic wall than among the muscles of the pelvic floor. The inconstant substance of the coccygeus muscle suggests that it may not be a reliable surgical landmark or a reliably available buffer between sharp instruments and fragile neurovascular structures. Neither should the absence of a conspicuous coccygeus on MRI or other imaging studies necessarily be interpreted as a sign of pelvic floor weakness when the iliococcygeus and pubococcygeus muscles appear normal.
A second difficulty with the traditional account of the pelvic floor muscles is that iliococcygeus has no attachment to the ilium. Despite its name, iliococcygeus attaches laterally to the tendinous arch of levator ani and to the pelvic surface of the ischial spine (Fig. 4.4.8). This is a minor point, however, and even if its name inaccurately describes its attachments, iliococ- cygeus belongs among the muscles of the pelvic floor.
Consideration of the actual configuration of the pelvic floor muscles suggests that even the term “pelvic floor” is somewhat misleading, since the pelvic floor is neither flat nor horizontal. Instead, the paired muscles of the pelvic floor form an obliquely oriented muscular funnel, higher posteriorly than anteriorly and slanting obliquely from superior attachments relatively high on the pelvic wall toward inferior attachments on the sacrum, coccyx, midline connective tissue structures, and connective tissue coats of the anorectum and vagina (Fig. 4.4.8). Neither is the pelvic floor shaped like a basin. In many textbook diagrams, the muscles of the pelvic floor are depicted as forming a shallow but capacious muscular basin with sides curving gently outward away from the pelvic organs. Recent MRI studies confirm, however, that the pelvic floor is closely contiguous with the pelvic organs11,12. The slanting surfaces of the muscles of the pelvic floor approach the sides of the pelvic organs, as well as their inferior portions, and the pelvic floor also supports the posterior surfaces of the vagina and rectum.
Recent dynamic MRI studies conducted by Hjartardottir and colleagues suggest that, at resting tone, the pelvic floor is convex superiorly rather than inferiorly and that it is shaped like a dome, and not a basin.30 Other MRI studies have reported similar results31,32 Hjartardottir and colleagues also suggest that the muscles of the pelvic walls straighten during muscular contraction, and that they are basin-shaped only when downwardly displaced by intra-abdominal pressure during the Valsalva maneuver.
In the following description, the muscles of the pelvic floor will be named according to their individual attachments, except for iliococcygeus. In the absence of detailed electromyographic or other studies of the individual muscles of the pelvic floor, their functions can be inferred only from their attachments and muscle fiber orientations. These inferences are provided in the following discussion, but they are largely hypothetic and await further study.
From fixed attachments to the tendinous arch of levator ani and the ischial spine, the paired iliococcygeus muscles descend in an obliquely horizontal path to converge posterior to the anorectum, where they form a strong median raphe (Fig. 4.4.8). The iliococcygeal raphe is attached anteriorly to the muscles and fibrous coat of the anorectum and to the anterior part of the anococcygeal ligament; the raphe is attached posteriorly to the coccyx and apex of the sacrum and to the posterior part of the anococcygeal ligament. The muscle fiber orientation and attachments of iliococcygeus suggest that bilateral contraction would draw the iliococcygeus raphe superiorly and anteriorly. Resting tone would support structures superior to iliococcygeus, including the levator plate, rectum, and vagina, and would help maintain the organs in their normal midline positions. Indirect effects of the bilateral contraction of iliococcygeus would be tension on any structures attached to the median raphe of iliococcygeus, such as the anus and the anococcygeal ligament.
Figure 4.4.8. Muscles of the pelvic floor; lateral oblique view with left os coxae distracted.
1 Tendinous arch of levator ani (condensation of investing fascia over the obturator internus muscle); 2 Iliococcygeus; 3 Pubovaginalis and puboperitonealis; 4 Puborectalis; 5 Pubococcygeus; 6 Levator plate; 7 Tendinous arch of the pelvic fascia.
Iliococcygeus receives its motor innervation directly from intrapelvic branches of S2A4, which enter its pelvic surface. Branches of the pudendal nerve, entering its perineal surface, may also provide innervation to iliococcygeus. The internal pudendal and inferior gluteal vessels provide the vascular supply to iliococcygeus. Intrapelvic somatic branches to iliococcygeus are vulnerable to injury during pregnancy and delivery, particularly vaginal delivery, or during any pelvic surgery.
The pubococcygeus muscle, or muscle complex, consists of lateral and medial parts (Fig. 4.4.8). The lateral pubococcygeal part extends between the pubis anteriorly and the coccyx and sacrum posteriorly. The medial part extends between the pubis anteriorly and the pelvic organs and perineal body posteriorly, and consists of the pubovaginalis, puboperinealis, puborectalis, and puboanalis muscles.*
Pubococcygeus ascends in an obliquely vertical path from anterior attachments to the pubis and pubic symphysis to posterior attachments on the coccyx, anterior sacrococcygeal ligament, and sacrum. Posterior to the rectum, the left and right pubococcygeus muscles form a broad aponeurosis, the tendinous plate of levator ani, or levator plate. The presacral fascia also contributes to the formation of the levator plate. Pubococcygeus has two fixed attachments, and its isometric contraction shortens the overall length of the muscle between the pubis and sacrum. Bilateral contraction of pubococcygeus would elevate the levator plate and the rectum and vagina which recline upon its sloping surface; resting tone would support these organs.
The muscle fibers of the pubococcygeus and iliococcygeus muscles run roughly perpendicular to one another, overlapping posterior to the rectum and connected to, or resting above, the anococcygeal ligament. Although it is true that iliococcygeus and pubococcygeus “support the pelvic organs”, this is a very general description of the more complex functions suggested by their attachments and muscle fiber orientations. In fact, iliococ- cygeus and pubococcygeus probably support the pelvic organs in several different ways.
(1) Their resting tone supports the pelvic organs lying above the levator plate of pubococcygeus and the median raphe of iliococcygeus.
(2) The attachment of iliococcygeus to the anococcygeal ligament supports the anus by reinforcing and elevating its posterior attachment to the coccyx.
(3) The balanced tone or balanced contraction of the paired iliococcygeus and pubococcygeus muscles helps stabilize the pelvic organs in their midline positions, minimizing strain on the visceral pelvic fascia anchoring them to the pelvic walls, and maintaining the vertical aligment between the pelvic organs, pelvic floor, and urinary and fecal continence mechanisms.
It is important to note that the stabilizing functions of iliococ- cygeus and pubococcygeus require that both the left and right muscles of each pair be intact and functioning. If either muscle of the pair is fibrotic, torn, avulsed from its attachment to the pelvic wall, or paralyzed from loss of its somatic motor innervation, then the intact contralateral muscle will tend to draw the iliococcygeal raphe away from the midline toward the intact side, and could conceivably place additional tension on the visceral pelvic fascial supports running from the organs to the pelvic walls on the affected side. Delancey and colleagues11 found both unilateral and bilateral damage to the pubococ- cygeus and iliococcygeus among primiparous women, but not among nulliparous controls.
*The Terminologia Anatomica recognizes the terms “puboprostaticus” (in males, although this muscle is more commonly referred to as “pubourethralis”), “pubo- vaginalis” (in females), “puboperinealis”, “puboanalis”, and “puborectalis”.33 The 39th British Edition of Gray's Anatomy recognizes “pubourethralis” (in males) “pubovaginalis” (in females), some unnamed muscle fibers from pubourethralis or pubovaginalis attaching to the perineal body, muscle fibers attaching to the anorectal junction (sometimes called “puboanalis”), and “puborectalis”.
The muscle fiber orientations and attachments of the medial part of the pubococcygeus complex suggest that pubo- vaginalis, puboperinealis, and puborectalis support the pelvic organs in yet another way. Fibers of the paired pubovaginalis muscles run posteriorly from the pubic symphysis, decussate, and blend with fibers from the opposite side to form a muscular sling posterior to the vagina; fibers also blend with the connective tissue of the vaginal wall. Fibers of the puboperinealis muscle detach from pubovaginalis and blend with the connective tissue of the perineal body. The urethra is closely approximated to the anterior wall of the vagina, and the resting tone of the sling formed by pubovaginalis would support both the vagina and urethra. Contraction of pubovaginalis would draw the vagina and urethra anteriorly and superiorly and might also have some effect on stabilizing the perineal body.
Fibers of the paired puborectalis muscles run posteriorly from the pubic symphysis, decussate, and blend with fibers from their contralateral counterparts to form a sling posterior to the rectum. Puborectalis is a substantial muscle, extending below the level of the other muscles of the pelvic floor. The sling formed by puborectalis surrounds the anorectal junction, drawing it anteriorly and forming a kink, the anorectal angle, which helps maintain fecal continence. Fibers of the puboanalis muscle contribute to the conjoint longitudinal coat of the anus, a layer of striated and smooth muscle fibers and fibroelastic tissue between the internal and external anal sphincters, and extending inferiorly, through fibroelastic connections, to the skin of the anus. Although it is true, in a fairly trivial way, that pubo- vaginalis and puborectalis “support” the pelvic organs, the actual mechanisms and vectors of support are very different from those of iliococcygeus and pubococcygeus. Pubovaginalis and puborectalis also hold the urethra, vagina, and rectum together in a block, approximate their walls,33 and maintain their vertical aligment.
Cooperation among the puborectalis, internal anal sphincter, and external anal sphincter is essential for continence, and maintaining the alignment of the rectum, puborectalis, and external and internal sphincters is essential for normal function. Relaxation of puborectalis, loss of alignment, injury to motor or proprioceptive nerve fibers supplying the rectum and its muscles, or herniation of the rectum through the posterior wall of the vagina can compromise normal bowel function. Obstetric trauma is the most common cause of external anal sphincter injury.34
Yucel and colleagues have suggested that the levator ani muscles do not support the proximal urethra and play no active role in continence.35 The relationship between pubovaginalis and the urinary continence mechanism is not obvious, but an interesting speculative possibility suggests itself. The paired compressor urethrae muscles attach posteriorly to the ischiopubic rami and runs anteriorly to form a sling around the urethra. The pubovaginalis sling and the compressor urethrae sling pull in opposite directions, and it is conceivable that contraction of pubovaginalis, which draws both vagina and urethra anteriorly, would increase the effectiveness of compressor urethrae, which draws the urethra posteriorly and compresses it against the anterior vaginal wall.
Pubococcygeurs, pubovaginalis, and puborectalis probably receive most of their innervation from the pudendal nerve (S2-4), although some intrapelvic somatic fibers may also reach their pelvic surfaces.
Tunn and colleagues11 found that detachment of the “pubo- visceral” portion is the most common levator ani injury during vaginal delivery, but that iliococcygeus may also be injured. Injury to the puborectalis muscle would have very different consequences from injury to the iliococcygeus muscle, and the distinction between injuries to different pubovisceral muscles would be helpful.
The volume of the levator ani muscle decreases with age,36 and fibrotic changes in the levator ani muscle of cadavers with vaginal parity have been documented.37 The association between pelvic nerve injury and pelvic floor dysfunction has also been documented.38,39
Visceral pelvic fascia and visceral fascial ligaments
The muscles of the pelvic floor and the midline connective tissue structures constitute the primary supports of the pelvic organs. The visceral pelvic fascia (endopelvic fascia) and visceral pelvic ligaments surround the pelvic organs; blend with the connective tissue of the pelvic organ walls; form partitions between the organs; and tie the pelvic organs to the pelvic walls, pelvic floor, and midline connective tissue structures. The connective tissue scaffold formed by condensations within the visceral pelvic fascia maintains the pelvic organs in their central positions and customary orientations, while allowing for continual changes in their shapes and relative positions.
The peritoneum is the mesothelial lining of the abominopelvic cavity. It follows the contours of the pelvic walls and drapes over the superior surfaces of the pelvic organs, the visceral pelvic fascia and the visceral ligaments formed by collagenous condensations within the visceral pelvic fascia, and pelvic neurovascular structures. Where peritoneum spans the distance between two pelvic organs, or between a pelvic organ and the pelvic walls, it may double back on itself to form peritoneal folds. The space between the layers of peritoneum forming the fold is filled by loose visceral pelvic fascia and may contain neurovascular structures.
The term “ligament”, as it is used in the anatomic and surgical literature, is at least as problematic as the term “fascia”. In the pelvis, structures described as “ligaments” include the sturdy interosseous ligaments of the bony pelvis (such as the sacrospinous and sacrotuberous ligaments), vestiges of embryonic structures draped in peritoneal folds (such as the median ligament of the bladder and round ligament of the uterus), and neurovascular structures draped in peritoneal folds (such as the lateral ligament of the bladder and lateral ligament of the rectum). Use of the term “ligament” may suggest a degree of substance and robusticity. This implication is often misleading, however, and it is important to distinguish between the visceral pelvic ligaments tethering the pelvic organs and the peritoneal folds or ligaments adorning them. The round ligament and the broad ligament of the uterus are frequently included among the uterine supports. Although the broad and round ligaments may help to maintain uterine position, they are unlikely to contribute significantly to uterine support.
Visceral pelvic fascia
The visceral pelvic fascia (endopelvic fascia) is a three-dimensional connective tissue layer extending anteriorly to the retropubic space (space of Retzius), posteriorly to the sacrum, laterally to the tendinous arch of the pelvic fascia and pelvic walls, superiorly to the peritoneum, and inferiorly to the investing pelvic fascia covering the muscles of the pelvic floor and to the perineal membrane and perineal body.
Figure 4.4.9. Visceral pelvic fascia and visceral pelvic ligaments; lateral oblique view with left os coxae distracted.
1 Tendinous arch of the pelvic fascia; 2 Pubovesical and pubourethral ligaments; 3 Pubocervical ligament; 4 Paracervical connective tissue; 5 Transverse cervical ligament (cardinal ligament of Mackenrodt); 6 Uterosacral ligament; 7 Posterior rectal ligament.
The visceral pelvic fascia is composed of fat cells interspersed with varying amounts of collagen, elastin and smooth muscle fibers.7,40 In some regions, the visceral pelvic fascia functions as a relatively amorphous packing material occupying the spaces between the pelvic organs, the peritoneum, and the pelvic walls and floor. The paravesical fascia, pararectal fascia, and the parametrium within the broad ligament are all examples of loose visceral pelvic fascia that fills the spaces around organs and provides passage for the nerves and vessels supplying the organs. Loose visceral pelvic fascia also extends into the peritoneal folds.
In other regions, the collagen fibers and elastin fibers of the visceral pelvic fascia coalesce to form sheaths around neurovascular structures, or condense to form a series of demonstrable ligaments attaching the pelvic organs to the investing pelvic fascia covering the pubis, pelvic walls and floor, and sacrum. The tendinous arch of the pelvic fascia (white line) is a condensation of the iliococcygeus investing fascia which extends anteriorly as the pubovesical ligaments and posteriorly to the ischial spine, where it becomes less distinct. The visceral fascial supports of the pelvic organs attach in a line along the tendinous arch of the pelvic fascia to the ischial spine, and then continue their attachment posteriorly to the investing coccygeus fascia and presacral fascia. Less conspicuous accumulations of collagen fibers and elastin fibers probably extend from the organs to the pelvic walls and floor wherever the visceral and investing pelvic fascias lie adjacent to one another.
Visceral fascial supports of the bladder and urethra
The pubovesical and puborurethal ligaments are sturdy condensations of visceral pelvic fascia extending anteriorly to the pelvic aspect of the pubic bones and transverse perineal ligament and laterally to the anterior part of the tendinous arch of the pelvic fascia. The retropubic venous plexus lies between the paired pubovesical and pubourethral ligaments. The pubourethral ligaments consist of dense fibrous connective tissue and smooth muscle fibers.41 MRI studies have found both thinning of the urethral striated muscle and distortion of the pubourethral ligaments in women with stress incontinence versus controls.42
The median ligament of the umbilicus and lateral ligament of the bladder are peritoneal folds rather than visceral fascial supports. The median umbilical ligament is a peritoneal fold surrounding the remnant of the embryonic urachus; the lateral ligament of the bladder is a peritoneal fold containing the superior vesical arteries in their course from the internal iliac artery to the superior portion of the bladder.
Visceral fascial supports of the cervix and vagina
The body of the uterus is relatively unencumbered by fascial supports, enabling it to change size and position, notably during pregnancy, or to respond to changes in the sizes and positions of the bladder and rectum on either side. All ligaments superior to the cervix are peritoneal ligaments. The uterus, uterine tubes, ovaries, and parametrium are draped in the peritoneum of the broad ligament; the ovarian and uterine vessels, lymphatics, and autonomic nerve plexuses traverse the parametrium to reach the uterus and adnexae. The uterovesical fold (anterior ligament of the uterus) and rectovaginal fold (posterior ligament of the uterus) are peritoneal folds surrounding a core of loose visceral pelvic fascia. The round ligament of the uterus, a vestigial structure containing smooth muscle and small blood vessels, passes from the uterine wall to the inguinal canal and labia majora.
The cervix and vagina are held comparatively immobile, although the vagina increases somewhat in length during sexual arousal. The vagina is a fibromuscular tube, which normally reclines obliquely on the rectum and levator plate. The urethra is virtually embedded in the anterior vaginal wall. A dense fascial condensation, the paracervical connective tissue, surrounds the cervix and provides reinforcement and attachment for the visceral fascial ligaments. Ligaments attaching to the paracervical connective tissue anchor the cervix to the pubis, tendinous arch of the pelvic fascia, ischial spine, coc- cygeus and piriformis fascia, and sacrum. The boundaries between the visceral fascial ligaments are somewhat arbitrary, and the names given the ligaments are roughly based on their attachments after development during dissection or surgery.
The pubocervical ligaments (anterior vaginal fascia), are sturdy condensations of endopelvic fascia extending anteriorly from the vagina and paracervical connective tissue to the tendinous arch of the pelvic fascia and pelvic surface of the pubic bones, and extending inferiorly to the perineal membrane, where they attach just lateral to the urethra. The vesical plexus runs within the pubocervical fascia.17 The paravaginal supports'3-45 are condensations of endopelvic fascia extending laterally from the vagina and cervix to the tendinous arch of the pelvic fascia.
The transverse cervical ligaments (cardinal ligaments, ligaments of Mackenrodt) are condensations of visceral pelvic fascia running from the vagina and paracervical connective tissue posterolaterally to the tendinous arch of the pelvic fascia and ischial spine.
The uterine artery enters the base of the transverse cervical ligament as it crosses the pelvic floor between the internal iliac artery and the lateral aspect of the cervix. The ureter also enters the base of the transverse cervical ligament, running posterior and inferior to the uterine artery to reach the trigone of the bladder. Autonomic nerve fibers of the hypogastric plexus accompany the ureter and uterine artery. The nerves are vulnerable to injury during delivery or pelvic surgery, including hysterectomy and pelvic floor repair.
The uterosacral ligaments (rectouterine folds) are condensations of visceral pelvic fascia extending from the paracervical fascia vaginal vault, where the ligament is thickest, to the coccygeus and piriformis parietal pelvic fascia and sacrum. The uterosacral ligament is palpable per rectum. The sacral attachment of the uterosacral ligament is, apparently, quite variable. Buller and Thompson46 identified a sacral attachment extending over the first three sacral vertebrae and variably over the fourth, Umek et al. identified a sacral attachment in only 7% of MRI studies,47 and Fritsch and Hotzinger48 found no sacral attachment in plastinated sections. Buller and Thompson also described three portions of the uterosacral ligament, and adjacent anatomic structures, in order to identify the safest site for vaginal vault fixation. These authors describe important associations between the sacral portion of the uterosacral ligament and the superior gluteal vein; between the intermediate portion of the ligament, the middle rectal artery, and “nerve elements”; and between the sacral portion and the ureter. They conclude that the optimum fixation site is the intermediate part of the uterosacral ligament. Nerve fibers traveling in the uterosacral ligament may include not only autonomic fibers traveling to the rectal, cervical, and vesical plexuses, but also intrapelvic somatic fibers traveling to the iliococcygeus muscle and possibly to other muscles of the pelvic floor.
Recent discussions and publications have referred to a cardinal uterosacral complex including both the transverse cervical ligament and the uterosacral ligament,10,44,49 and the paravaginal supports and pubocervical ligament could also be logically included in the series of visceral fascial supports extending from the cervix and vagina to the pelvic walls.
The rectovaginal fascia (rectovaginal septum, posterior vaginal fascia, or Denonvillier’s fascia) is derived embryonically from a double-layered peritoneal fold that extended inferiorly between the cervix and vagina anteriorly and the rectum posteriorly, and that fused during development. The rectovaginal fascia forms a septum between the two organs and attaches laterally to the cardinal-uterosacral complex and inferiorly to the perineal body. The intact rectovaginal fascia forms an important posterior support for the vaginal wall and a barrier to encroachment of the rectum into the posterior vaginal wall in a rectocele.7
Another recent trend in the literature is to distinguish anterior and posterior compartments relative to the supports of the cervix and vagina.10 According to this terminology, the vagina and uterus, and the visceral pelvic supports attaching them to the pelvic walls, separate the pelvis into an anterior compartment including the urethra and bladder and a posterior compartment including the anus and rectum. Failure of the uterine and vaginal visceral fascial supports can lead to descent of the cervix within the vagina or even outside the vagina (vaginal vault prolapse and procidentia). Failure of the anterior compartment supports can lead to protrusion of a portion of the bladder or urethra into the anterior vaginal wall (cystocele or urethrocele). Failure of the posterior compartment supports can lead to protrusion of a portion of the rectum or small intestine into the posterior vaginal wall. Multicompartment failures may also occur.
Visceral fascial supports of the rectum and anorectum
Condensations of the visceral pelvic fascia anchor the rectum to the pelvic surface of the sacrum and to the tendinous arch of the pelvic fascia. The posterior rectal ligaments (Waldeyer’s fascia) are sturdy attachments between the fibrous coat of the anorec- tum and the third and fourth sacral vertebrae. The lateral rectal ligaments are usually considered as peritoneal folds surrounding the middle rectal arteries.19 Based on cadaver dissections, Jones and colleagues have doubted the existence of substantial lateral rectal ligaments and found only small or unilaterally present middle rectal arteries.50
It is important to note that the visceral investing supports attach the anterior walls of the bladder and urethra to the pubic symphysis and attach the posterior walls of the rectum and anus to the sacrum. The pubocervical ligaments anchor the vagina anteriorly to the pubis but provide no barrier between the walls of the urethra and vagina; in fact, the urethra is virtually embedded in the anterior vaginal wall. The rectovaginal fascia does provide a barrier between the vagina and rectum, and defects in the rectovaginal fascia are associated with rectocele.
The anatomy of the pelvic organ support system is complex and defies easy characterization. Traditional anatomic descriptions of the pelvic organ support system appear to be inadequate for the rapidly accumulating body of data on normal and pathologic pelvic floor anatomy. Misconceptions about the extent and configurations of the pelvic floor, an inadequate and confusing terminology, and a proliferation of undefined synonyms and landmarks in the recent literature are all obstacles to an adequate understanding of pelvic floor anatomy. Recent technological advances offer the opportunity to study pelvic floor anatomy in powerful and exciting ways, but until conceptual and terminological difficulties are resolved, these studies cannot achieve their full potential for improving the understanding, diagnosis, and treatment of pelvic floor disorders.
The pelvic organ support system consists of four basic components:
(1) pelvic bones, joints, and interosseous ligaments
(2) midline connective tissue structures of the pelvic outlet
(3) pelvic muscles and investing pelvic fascia
(4) visceral pelvic fascia and visceral fascial ligaments.
The importance of the midline connective tissue structures is overlooked in most discussions of the pelvic organs support system.
The nearly ubiquitous idea that the pelvic floor muscles comprise a single levator ani muscle with a single function, “supporting the pelvic floor”, is an impediment to more detailed study of the actual functions and dysfunctions of the muscles of the pelvic floor. Attention to the attachments and muscle fiber orientations of the individual pelvic floor muscles suggest that their functions are more complex, more interesting, and probably more clinically relevant than the description “supporting the pelvic floor” would suggest. The functions of individual muscles merit further research. Additional studies are also needed to determine how the components of the pelvic floor support system work together, their relative contributions to pelvic organ support, and the consequences of the failure of one component for other components of the pelvic floor support system.
The somatic innervation to muscles of the pelvic floor, continence mechanisms, and pelvic organs may have both intrapelvic and extrapelvic courses. These nerves are particularly vulnerable to injury in surgical procedures involving the sacrospinous ligament and uterosacral ligament.
The increasing incidence of pelvic organ prolapse and the low success rates of many very invasive surgical procedures suggest that additional clarification of the pelvic floor support system is urgently needed.
I am grateful to Dr Richard F Hoyt, for his encyclopedic knowledge of anatomy, sound judgment, and deft editorial pencil, and to David Chapin, for his superb summary of pelvic floor supports.
1. Nygaard I, Bradley C et al. Pelvic organ prolapse in older women: Prevalence and risk factors. O&tetGÆe£Ql 2004; 104(3): 489-97.
2. Tarnay CM, Bhatia NN. Urogynecology. In DeCherney AH and Nathan L, eds. Current Obstetric and Gynecologic Diagnosis and Treatment, 9th edition. New York: McGraw-Hill, 2003.
3. Olsen AL, Smith VJ, Bergstrom JO, Colling JC, Clark AL. Epidemiology of surgically managed pelvic organ prolapse and urinary incontinence. ObtetGynecol 1997; 89: 501-6.
4. Leslie Wilson L, Brown JS et al. Annual direct cost of urinary incontinence. Obstet Gynecol 2001; 98: 398-406.
5. Mant J, Painter R, Vessey M. Epidemiology of genital prolapse: observations from the Oxford Family Planning Association Study. Br J Obstet Gynecol 1997; 104: 579-85.
6. Whiteside JL, Weber AM et al. Risk factors for recurrent prolapse after vaginal repair. AmJO&tetGyMSol 2004; 191:1533-8.
7. Cundiff GW, Fenner D. Evaluation and treatment of women with rectocele: focus on associated defecatory and sexual dysfunction. Obstet Gynecol 2004; 104: 1403-21.
8. Strohbein K. Normal pelvic floor anatomy. Obstet Gynecol Clin North Am 1998; 25: 689-705.
9. Fielding JR. Practical MR imaging of female pelvic floor weakness. Radiographics 2002; 22: 295-304
10. Delancey JO, Kearney R et al. The appearance of levator ani muscle abnormalities in magnetic resonance images after vaginal delivery. OhtetGynecol 2003; 101: 46-53.
11. Tunn R, Delancey JO. Anatomic variations in the levator ani muscle, endopelvic fascia, and urethra in nulliparas evaluated by magnetic resonance imaging. Am J Obstet Gynecol 2003; 188: 116-21.
12. Hoyte L. Levator ani thickness variations in symptomatic and asymptomatic women using magnetic resonance-based-3-dimensional color mapping. Obstet Gynecol 2004; 103: 447-51.
13. Hoyte L, Schierlitz L, Zou K, Flesh G, Fielding JR.Two- and 3dimensional MRI comparison of levator ani structure, volume, and integrity in women with stress incontinence and prolapse. Am J Obstet Gynecol 2001; 185: 11-19
14. Williams PL, Bannister LH, Berry MM et al., eds. Gray’s Anatomy of the Human Body, 38th edn. New York: Churchill Livingstone, 1995: 1842.
15. Baragi RV, Delancey JO et al. Differences in pelvic floor area between African American and European American women. Am J Obstet Gynecol 2002; 187: 111-5.
16. Hoyt RF. Innervation of the vagina and vulva. In Goldstein I, Meston C, Davis S and Traish A eds. Women’s Sexual Function and Dysfunction, London: Taylor and Francis, 2005: 113-124.
17. Welgoss JA, Vogt VY, et al. Relationship between surgically induced neuropathy and outcome of pelvic organ prolapse surgery. Int Urogynecol J Pelvic Floor Dysfunct 1999; 10: 11-14.
18. Federative Committee on Anatomical Terminology. Terminologia Anatomica. New York: Thieme, 1998.
19. Williams PL, Bannister LH, Berry MM et al., eds. Gray’s Anatomy of the Human Body, 38th ed. New York: Churchill-Livingstone, 1995.
20. Drake RL, Vogel W et al. Gray’s Anatomy for Students. New York: Elsevier, 2005.
21. Rosse C, Gaddum-Rosse P, eds. Hollinshead’s Textbook of Anatomy, 5th ed. Philadelphia: Lippincott-Raven, 1997.
22. Moore KF, Dailey AF. Clinically Oriented Anatomy, 4th edition. Philadelphia: Lippincott, Williams and Wilkins, 1999.
23. Snell RS. Clinical Anatomy for Medical Students. Boston: Little Brown and Company, 1995.
24. Putz R, Pabst R. Sobotta’s Atlas of Human Anatomy. Philadelphia: Lippincott, Williams and Wilkins, 2000.
25. Lockhart RD, Hamilton GF, Fyfe FW. Anatomy of the Human Body. Philadelphia: JB Lippincott, 1965.
26. Standring S, ed. Gray’s Anatomy of the Human Body, 39th Ed. New York: Churchill Livingstone, 2005.
27. Strohbehn K, Ellis JH et al. Magnetic resonance imaging of the levator ani with anatomic correlation. Am J Obstet Gynecol 1996; 87: 277-85.
28. Singh K, Jakab M, Reid WM, Berger LA, Hoyte L. Three-dimensional magnetic resonance imaging assessment of levator ani morphologic features in different grades of prolapse. Am J Obstet Gynecol 2003; 188: 910-15.
29. Kearney R, Sawhney R, Delancey JO. Levator ani muscle anatomy evaluated by origin-insertion pairs. ObtetGySecol 2004; 104: 168-73.
30. Hjartardottir S, Nilsson J, Petersen C, Lingman G. The female pelvic floor: a dome - not a basin. Acta Obstet Gynecol Scand 1997; 76: 567-71.
31. Aukee P, Usenius JP, Kirkinen P. An evaluation of pelvic floor anatomy and function by MRI. Eur J Obstet Gynecol Reprod Biol 2004; 112: 84-8.
32. Schmeiser G, Putz R. The anatomy and function of the pelvic floor. Radiologe 2000; 40: 429-36.
33. Delancey JO. Structural anatomy of the posterior pelvic compartment as it relates to rectocele. Am J Obstet Gynecol 2004; 180: 815-23.
34. Rao SS. Pathophysiology of adult fecal incontinence. Gastroenterology 2004; 126 (Suppl): S14-22.
35. Yucel S, Baskin LS. An anatomical description of the male and female urethral sphincter complex. J Urol 2004; 171: 1890-7.
36. Copas P, Bukovsky A, Asbury B, Elder RF, Caudle MR, Estrogen, progesterone, and androgen receptor expression in levator ani muscle and fascia. J Womens Health 2001; (Larchmt) 10: 785-95.
37. Dimpfl T, Jaegar C, Mueller-Felber W et al. Myogenic changes of the levator ani muscle in premenopausal women: the impact of vaginal delivery and age. NeuoMrolUrodyn 1998; 17: 197-206.
38. Smith ARB, Hosker GL, Warrell DW. The role of partial denervation of the pelvic floor in the aetiology of genitourinary prolapse and stress incontinence of urine: a neurophysiological study. Br J Obstet Gynaecol 1989; 96: 24-8.
39. Snooks SJ, Swash M, Mathers SE, Henry MM. Effect of vaginal delivery on the pelvic floor: A 5-year follow-up. Br J Surg 1990; 77: 1358-60.
40. Strohbein K. Normal pelvic floor anatomy. Obstet Gynecol Clin North Am 1998; 25: 689-705.
41. Vazzoler N, Soulie M, Escourrou G et al. Pubourethral ligaments in women: anatomical and clinical aspects. Surg Radiol Anat 2002; 24: 33-7.
42. Kim JK, Kim YJ, Choo MS, Cho KS. The urethra and its supporting structures in women with stress urinary incontinence: MR imaging using an endovaginal coil. Am J Roentgenol 2003; 180: 1037-44.
43. Richardson AC, Edmonds PB, Williams NL. Treatment of stress urinary incontinence due to paravaginal fascial defect. Obstet Gynecol 1981; 57: 357-62.
44. Delancey JO. The anatomy of the pelvic floor. Curr Opin Obstet Gynecol 1994; 6: 313-6.
45. Delancey JO. Structural anatomy of the posterior pelvic compartment as it relates to rectocele. Am J Obstet Gynecol 2004; 180: 815-23.
46. Buller JL, Thompson JR. Uterosacral ligament: description of anatomic relationships to optimize surgical safety. Obstet Gynecol 2001; 97: 873-9.
47. Umek WH, Morgan DM et al. Quantitative analysis of uterosacral ligament origin and insertion points by magnetic resonance imaging. ObstelGynecÀ 2004; 103: 447-51.
48. Fritsch H, Hotzinger H. Tomographical anatomy of the pelvis, visceral pelvic connective tissue, and its compartments. Clin Anat 1995; 8: 17-24.
49. Chapin DS. The anatomy of pelvic supports. Presentation to Applied Clinical Anatomy course, Harvard Medical School. August 2000.
50. Jones OM, Smeulders N. Lateral ligaments of the rectum: an anatomical study. Br J Surg 1999; 86(4): 487-9