These bones together with the holy-bone, make that pelvis or Dish which containeth part of the guts, the bladder and the womb. CROOKE Body of Man, 118, 1615
Development of the pelvis
Development of the innominate bone and sacrum
Hyaline cartilage is first laid down as the model for the several elements of the pelvic bone that will form the ilium, ischium , and pubis ( Figs. 10-1 B, C). The first ossification center to appear is that of the ilium in the second month; the last center, that of the pubis, appears in the fourth or fifth months. Eventually, the whole mass of cartilage turns into bone. The appearance and fusion of the centers proceeds with considerable individual variation in addition to differences because of gender. The process occurs earlier in the female than in the male, especially with the onset of adolescence. For example, the ischium and pubis fuse to form the pubic ramus in the seventh to eighth year of life, whereas secondary centers in the iliac crest, acetabulum, and ischial tuberosity do not appear until puberty and fuse with the other ossified parts between the 15th and 25th years. At birth, large remnants of cartilage persist in each part. Secondary sites of ossification are indicated with dashed lines; these will appear at puberty and be united by the 25th year.
Up to the fifth week, the neural tube and gut extend into the tail bud, from which the sacrum and coccyx develop; however, by the eighth week, the bud, tube, and gut have regressed, leaving the bony structures behind.
The five elements of the sacrum are similar to those of the other vertebrae. Ossification centers for the body center and each half of the vertebral arch appear between the 10th and 20th weeks, whereas those for the costal elements appear much later, in the sixth to eighth months of gestation ( Fig. 10-1 A). Fusion of the sacral bodies begins in the sixth week, with the middle intervertebral disk fusing first and the first intervertebral disk fusing last.
The shape of the original cartilages of the pelvic bones is different in males and females. Even in fetal life, the subpubic angle or arch is wider in females than in males. After birth, male infants have larger pelves overall, but in female infants, the pelvic cavity is larger, the difference being greatest at 22 months and decreasing in subsequent years.
Gender differences in the pelvis in adults are influenced by the functions of locomotion in the male and childbearing in the female. In general, the male pelvis resembles a cone, whereas the female pelvis resembles a cylinder. The male pelvis is more heavily muscled, so that even though the cavity within the bony pelvis is larger, the net space is smaller. The various zones for muscular attachments are more clearly demarcated. Moreover, the bones themselves are heavier, especially the iliac crest, which curves more medially at its anterior projection. In the female, the blades of the ilia are oriented more vertically but are shorter, resulting in a smaller iliac fossa.
The musculature and fascia of the pelvic floor are derived from the tissues of the lumbar body wall and are supplied by nerves from the lumbar cord. The levator ani arises from the primitive tail musculature and thus has sacral innervation.
The development of the pelvic contents is described under the headings of the organ systems.
Individual variations in pelvic form are the rule and are, in part, influenced by abnormal hormonal environment during development. Some investigators feel that sacral anomalies fall into three definite patterns: (1) absent vertebra (the “agenetic” group, corresponding to “caudal regression syndrome”) ( Figs. 10-2 and 10-3 ); (2) hemivertebrae (the “dysgenetic” group); and (3) deficiencies of the neural arch (the “dysraphic” group) ( Fig. 10-4 ). Patients in group 1 have relative neurologic sparing and a relatively low incidence of visceral congenital anomalies. Those in group 2 have a high incidence of visceral abnormalities, but the neurologic deficit is minimal and usually only the bladder is denervated. Individuals in group 3 are prone to have sacral spina bifida with meningocele or myelomeningocele at the sacral level, with denervation of the lower urinary tract. Sacral and coccygeal anomalies are common with malformations of the distal lumbar spine. Regression of the tail bud may be asymmetric, leaving the pelvis tilted. The fifth lumbar vertebra may become assimilated into the sacrum, resulting in another promontory at a higher level. Bladder exstrophy is regularly accompanied by a variety of defects, including absence of the pubic symphysis with externally rotated pelvic girdle ( Fig. 10-5 ).
Structure of the pelvis
The surgical approach to the pelvis is different from the approach to the perineum. Even though the two spaces are contiguous, they will be considered separately.
Pelvic surgery means surgery within the lesser or true pelvis, the cylindric cavity within the bony pelvis. It is distinguished from the bowl-shaped greater or false pelvis, which is actually a region of the abdomen.
The pelvic cavity proper begins at the pelvic inlet, marked by a line drawn anteriorly from the upper border of the pubic bone and the pectineal line. The arcuate line of the ilium marks it laterally, and the promontory of the sacrum marks it behind. The boundary below is the pelvic outlet (inferior pelvic aperture), which is rimmed by the inferior surfaces of the ischiopubic arch, the sciatic notches, and the greater and lesser sciatic foramina.
Paired innominate bones make up the anterior and lateral parts of the bony pelvis, and the sacrum forms the posterior wall. Each innominate bone has three parts: (1) ilium, (2) ischium, and (3) pubis ( Fig. 10-6 ).
The ilium has the shape of a wedge. The wider part of the wedge begins near the anterior inferior iliac spine , first running anteriorly and upward to the anterior superior iliac spine , then making a wide sweep over the iliac crest , tapering to the posterior superior and posterior inferior iliac spines and the greater sciatic notch.
The ischium and pubis , as parts of the innominate bones, are described in the sections on the inguinal region (see Fig. 9-5 ) and the perineum (see Fig. 11-3 ), respectively. Together, these heavy bones provide the framework for support of the body and a base of action for the muscles of locomotion.
In the female, the false pelvis is wider than in the male because of the spread of the ilium at the anterior superior spine. The pelvic outlet is also wider and more circular because it is encroached on less by the ischial tuberosities and ischial spines.
Pelvis, posterior aspect
For a surgical approach to the dorsal and ventral spinal nerve roots, the anatomy of the posterior aspect of the pelvis is important.
The median sacral crest runs down the center of the sacrum and is surmounted by four spinous tubercles . Four dorsal sacral foramina form a row on either side of the median crest; each of these provides egress for the dorsal ramus of a spinal nerve ( Fig. 10-7 ). An intermediate sacral crest composed of four vestigial articular tubercles runs medial to the foramina. A lateral sacral crest , a remnant of fused transverse processes, lies lateral to the foramina. The sacral hiatus opens caudal to the lower tubercle and communicates with the spinal canal. The coccygeal cornua are vestiges of the fifth articular tubercles.
The cauda equina and filum terminale lie within the sacral canal (see Fig. 4-4 ). The meninges that define the subdural and subarachnoid spaces are fused in the middle of the sacrum so that the lower sacral nerves and filum terminale must traverse their walls to reach the foramina. The fifth sacral spinal nerve and the filum leave the canal through the sacral hiatus.
Pelvic ligaments, posterior view
Because of their relation to structures encountered during pelvic surgery, two pelvic ligaments are of urologic concern. The long sacrotuberous ligament attaches the ilium to the sacrum and joins the sacrum with the ischium. It runs as a thick, narrow band from the posterior iliac spine to the lower sacral tubercles and the adjacent lateral sacral border and ends on the medial margin of the ischial tuberosity ( Fig. 10-8 ). It continues along the ischial ramus as the falciform process . The thinner sacrospinous ligament attaches the ischial spine to the lateral sacral border, crossing in front of the sacrotuberous ligament. The greater sciatic foramen opens above the two ligaments as they cross the pelvis; the lesser sciatic foramen lies below.
The iliolumbar ligament connects the ilium to the fifth lumbar vertebra. Short dorsal sacroiliac ligaments run upward obliquely to connect the upper portions of the sacrum to the ilium; the long dorsal sacroiliac ligament has similar connections for the lower portions. The sacrospinous ligament joins the lateral margins of the sacrum to the spinous tubercle of the ilium over the medial spinous process of the sacrum in continuity with the sacrococcygeal ligament .
The uppermost ligament within the pelvis is the ventral sacroiliac ligament, a thickening of the fibrous capsule of the sacroiliac joint, most developed at the level of the arcuate line and the level of the posterior inferior iliac spine. The dominant ligament, however, is the interosseous sacroiliac ligament that bonds the sacrum and ilium firmly about the sacroiliac joint.
Peritoneal relationships in the male
The upper surfaces of the pelvic organs are covered with peritoneum, which also lines the rectovesical pouch (cul-de-sac) lying between the bladder and upper ends of the seminal vesicles and the rectum ( Fig. 10-9 ). Extending caudally from the pouch is a fused double fold of the inner stratum of the extraperitoneal connective tissue that was left behind after the absorption of the overlying peritoneum. This forms the anterior layer of Denonvilliers’ fascia (see Fig. 14-19 ).
Fibroareolar ligaments support the bladder and prostate ( Table 10-1 ). They are called true ligaments, in contrast to the peritoneal folds that also connect the bladder to the pelvic walls. The lateral true ligaments of the bladder, derived from the transversalis (endopelvic) fascia over the levators (see Fig. 10-12 ), connect it to the tendinous arch of the endopelvic fascia (not to be confused with the tendinous arch, which serves as site of attachment of the levator ani). The lateral puboprostatic ligaments do the same for the prostate. The medial puboprostatic ligaments (the familiar puboprostatic ligaments) attach the prostate to the back of the pubis and constitute the floor of the retropubic space. The posterior ligaments are condensations of the vesical venous plexus that run to the internal iliac veins posterolaterally.
|Ligament||Origin||Terminus||Resulting Anatomic Feature|
|FIBROAREOLAR (TRUE) LIGAMENTS|
|Lateral true ligaments of the bladder||Bladder||Tendinous arch of the pelvic fascia||—|
|Lateral puboprostatic ligament||Prostatic sheath||Tendinous arch||Medial inguinal fossa|
|Medial puboprostatic ligament (pubovesical) ligament||Prostatic sheath||Back of pubic bone||Floor of retropubic space|
|Posterior ligaments||Lateral border of bladder base with vesical venous plexus||Internal iliac veins||—|
|Median umbilical fold (contains urachus)||Bladder||Umbilicus||Supravesical fossae|
|Medial umbilical folds (contain obliterated umbilical arteries)||Bladder||Umbilicus||Paravesical fossae|
|Lateral umbilical folds (contain inferior epigastric arteries)||Bladder||Pelvic sidewalls||Lateral inguinal fossae|
|Sacrogenital folds||Bladder||Sacrum||Pararectal fossae|