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Chapter 6 The Pelvis: Part I—The Pelvic Walls A 51-year-old man was involved in a light-plane accident. He was flying home from a business trip when, because of fog, he had to make a forced landing in a plowed field. On landing, the plane came abruptly to rest on its nose. His companion was killed on impact, and he was thrown from the cockpit. On admission to the emergency department, he was unconscious and showed signs of severe hypovolemic (loss of circulating blood) shock. He had extensive bruising of the lower part of the anterior abdominal wall, and the front of his pelvis was prominent on the right side. During examination of the penis, it was possible to express a drop of blood-stained fluid from the external orifice. No evidence of external hemorrhage was present. Radiographic examination of the pelvis showed a dislocation of the symphysis pubis and a linear fracture through the lateral part of the sacrum on the right side. The urethra was damaged by the shearing forces applied to the pelvic area, which explained the blood-stained fluid from the external orifice of the penis. The pelvic radiograph (later confirmed on computed tomography scan) also revealed the presence of a large collection of blood in the loose connective tissue outside the peritoneum, which was caused by the tearing of the large, thin-walled pelvic veins by the fractured bone and accounted for the hypovolemic shock. This patient illustrates the fact that in-depth knowledge of the anatomy of the pelvic region is necessary before a physician can even contemplate making an initial examination and start treatment in cases of pelvic injury. Chapter Objectives

  • The pelvis is a bowl-shaped bony structure that protects the terminal parts of the gastrointestinal tract and the urinary system and the male and female internal organs of reproduction.
  • It also contains important nerves, blood vessels, and lymphatic tissues.
  • The purpose of this chapter is to review the significant anatomy of the pelvic walls relative to clinical problems. Particular attention is paid to age and sexual differences and to the anatomic features associated with pelvic examinations.

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Basic Anatomy The pelvis* is the region of the trunk that lies below the abdomen. Although the abdominal and pelvic cavities are continuous, the two regions are described separately. The Pelvis The bony pelvis’s main function is to transmit the weight of the body from the vertebral column to the femurs. In addition, it contains, supports, and protects the pelvic viscera and provides attachment for trunk and lower limb muscles. The bony pelvis is composed of four bones: the two hip bones, which form the lateral and anterior walls, and the sacrum and the coccyx, which are part of the vertebral column and form the back wall (Fig. 6-1). The two hip bones articulate with each other anteriorly at the symphysis pubis and posteriorly with the sacrum at the sacroiliac joints. The bony pelvis thus forms a strong basin-shaped structure that contains and protects the lower parts of the intestinal and urinary tracts and the internal organs of reproduction. The pelvis is divided into two parts by the pelvic brim, which is formed by the sacral promontory (anterior and upper margin of the first sacral vertebra) behind, the iliopectineal lines (a line that runs downward and forward around the inner surface of the ileum) laterally, and the symphysis pubis (joint between bodies of pubic bones) anteriorly. Above the brim is the false pelvis, which forms part of the abdominal cavity. Below the brim is the true pelvis. Orientation of the Pelvis It is important for the student, at the outset, to understand the correct orientation of the bony pelvis relative to the trunk, with the individual standing in the anatomic position. The front of the symphysis pubis and the anterior superior iliac spines should lie in the same vertical plane. This means P.309
that the pelvic surface of the symphysis pubis faces upward and backward and the anterior surface of the sacrum is directed forward and downward.

Figure 6-1 Anterior view of the male pelvis (A) and female pelvis (B).

False Pelvis The false pelvis is of little clinical importance. It is bounded behind by the lumbar vertebrae, laterally by the iliac fossae and the iliacus muscles, and in front by the lower part of the anterior abdominal wall. The false pelvis flares out at its upper end and should be considered as part of the abdominal cavity. It supports the abdominal contents and after the third month of pregnancy helps support the gravid uterus. During the early stages of labor, it helps guide the fetus into the true pelvis. True Pelvis Knowledge of the shape and dimensions of the female pelvis is of great importance for obstetrics, because it is the bony canal through which the child passes during birth. The true pelvis has an inlet, an outlet, and a cavity.

  • The pelvic inlet, or pelvic brim (Fig. 6-2), is bounded posteriorly by the sacral promontory, laterally by the iliopectineal lines, and anteriorly by the symphysis pubis (Fig. 6-1). P.310
    Figure 6-2 Right half of the pelvis showing the pelvic inlet, pelvic outlet, and sacrotuberous and sacrospinous ligaments.
  • The pelvic outlet (Fig. 6-2) is bounded posteriorly by the coccyx, laterally by the ischial tuberosities, and anteriorly by the pubic arch (Figs. 6-2 and 6-3). The pelvic outlet has three wide notches. Anteriorly, the pubic arch is between the ischiopubic rami, and laterally are the sciatic notches. The sciatic notches are divided by the sacrotuberous and sacrospinous ligaments (Figs. 6-1 and 6-2) into the greater and lesser sciatic foramina (see page 318). From an obstetric standpoint, because the sacrotuberous ligaments are strong and relatively inflexible, they should be considered to form part of the perimeter of the pelvic outlet. Thus, the outlet is diamond shaped, with the ischiopubic rami and the symphysis pubis forming the boundaries in front and the sacrotuberous ligaments and the coccyx forming the boundaries behind.
  • The pelvic cavity lies between the inlet and the outlet. It is a short, curved canal, with a shallow anterior wall and a much deeper posterior wall (Fig. 6-2).

Structure of the Pelvic Walls The walls of the pelvis are formed by bones and ligaments that are partly lined with muscles covered with fascia and parietal peritoneum. The pelvis has anterior, posterior, and lateral walls and an inferior wall or floor (Fig. 6-6). Anterior Pelvic Wall The anterior pelvic wall is the shallowest wall and is formed by the bodies of the pubic bones, the pubic rami, and the symphysis pubis (Fig. 6-7). Posterior Pelvic Wall The posterior pelvic wall is extensive and is formed by the sacrum and coccyx (Fig. 6-8) and by the piriformis muscles (Fig. 6-9) and their covering of parietal pelvic fascia. Sacrum The sacrum consists of five rudimentary vertebrae fused together to form a single wedge-shaped bone with a forward concavity (Figs. 6-2 and 6-8). The upper border or base of the bone articulates with the fifth lumbar vertebra. The narrow inferior border articulates with the coccyx. Laterally, the sacrum articulates with the two iliac bones to form the sacroiliac joints (Fig. 6-1). The anterior and upper margins of the first sacral vertebra bulge forward as the posterior margin of the pelvic inlet—the sacral promontory (Fig. 6-2)—which is an important obstetric landmark used when measuring the size of the pelvis. The vertebral foramina together form the sacral canal. The laminae of the fifth sacral vertebra, and sometimes those of the fourth, fail to meet in the midline, forming the sacral hiatus (Fig. 6-8). The sacral canal contains the anterior and posterior roots of the lumbar, sacral, and coccygeal spinal nerves; the filum terminale; and fibrofatty material. It also contains the lower part of the subarachnoid space down as far as the lower border of the second sacral vertebra (Fig. 6-10). The anterior and posterior surfaces of the sacrum possess on each side four foramina for the passage of the anterior and posterior rami of the upper four sacral nerves (Fig. 6-8). P.311

Figure 6-3 Right hip bone. A. Medial surface. B. Lateral surface. Note the lines of fusion between the three bones—the ilium, the ischium, and the pubis.

Clinical Notes Clinical Concept: The Pelvis Is a Basin with Holes in Its Walls The walls of the pelvis are formed by bones and ligaments; these are partly lined with muscles (obturator internus and piriformis) covered with fascia and parietal peritoneum. On the outside of the pelvis are the attachments of the gluteal muscles and the obturator externus muscle. The greater part of the bony pelvis is thus sandwiched between inner and outer muscles. The basin has anterior, posterior, and lateral walls and an inferior wall or floor formed by the important levator ani and coccygeus muscles and their covering fascia. The basin has many holes: The posterior wall has holes on the anterior surface of the sacrum, the anterior sacral foramina, for the passage of the anterior rami of the sacral spinal nerves. The sacrotuberous and sacrospinous ligaments convert the greater and lesser sciatic notches into the greater and lesser sciatic foramina. The greater sciatic foramen provides an exit from the true pelvis into the gluteal region for the sciatic nerve, the pudendal nerve, and the gluteal nerves and vessels; the lesser sciatic foramen provides an entrance into the perineum from the gluteal region for the pudendal nerve and the internal pudendal vessels. (One can make a further analogy here: For the wires to gain entrance to the apartment below, without going through the floor, they have to pierce the wall [greater sciatic foramen] to get outside the building and then return through a second hole [lesser sciatic foramen]. In the case of the human body, the pudendal nerve and internal pudendal vessels are the wires and the levator ani and the coccygeus muscles are the floor.) The lateral pelvic wall has a large hole, the obturator foramen, which is closed by the obturator membrane, except for a small opening that permits the obturator nerve to leave the pelvis and enter the thigh. Pelvic Measurements in Obstetrics The capacity and shape of the female pelvis are of fundamental importance in obstetrics. The female pelvis is well adapted for the process of childbirth. The pelvis is shallower and the bones are smoother than in the male. The size of the pelvic inlet is similar in the two sexes, but in the female, the cavity is larger and cylindrical and the pelvic outlet is wider in both the anteroposterior and the transverse diameters. Four terms relating to areas of the pelvis are commonly used in clinical practice:

  • The pelvic inlet or brim of the true pelvis (Fig. 6-4) is bounded anteriorly by the symphysis pubis, laterally by the iliopectineal lines, and posteriorly by the sacral promontory.
  • The pelvic outlet of the true pelvis (Fig. 6-4) is bounded in front by the pubic arch, laterally by the ischial tuberosities, and posteriorly by the coccyx. The sacrotuberous ligaments also form part of the margin of the outlet.
  • The pelvic cavity is the space between the inlet and the outlet (Fig. 6-4).
  • The axis of the pelvis is an imaginary line joining the central points of the anteroposterior diameters from the inlet to the outlet and is the curved course taken by the baby’s head as it descends through the pelvis during childbirth (Figs. 6-4 and 6-5A).

Internal Pelvic Assessments Internal pelvic assessments are made by vaginal examination during the later weeks of pregnancy, when the pelvic tissues are softer and more yielding than in the newly pregnant condition.

  • Pubic arch: Spread the fingers under the pubic arch and examine its shape. Is it broad or angular? The examiner’s four fingers should be able to rest comfortably in the angle below the symphysis.
  • Lateral walls: Palpate the lateral walls and determine whether they are concave, straight, or converging. The prominence of the ischial spines and the position of the sacrospinous ligaments are noted.
  • Posterior wall: The sacrum is palpated to determine whether it is straight or well curved. Finally, if the patient has relaxed the perineum sufficiently, an attempt is made to palpate the promontory of the sacrum. The second finger of the examining hand is placed on the promontory, and the index finger of the free hand, outside the vagina, is placed at the point on the examining hand where it makes contact with the lower border of the symphysis. The fingers are then withdrawn and the distance measured (Fig. 6-5B), providing the measurement of the diagonal conjugate, which is normally about 5 in. (13 cm). The anteroposterior diameter from the sacrococcygeal joint to the lower border of the symphysis is then estimated.
  • Ischial tuberosities: The distance between the ischial tuberosities may be estimated by using the closed fist (Fig. 6-5D). It measures about 4 in. (10 cm), but it is difficult to measure exactly.

Needless to say, considerable clinical experience is required to be able to assess the shape and size of the pelvis by vaginal examination. The Female Pelvis Deformities of the pelvis may be responsible for dystocia (difficult labor). A contracted pelvis may obstruct the normal passage of the fetus. It may be indirectly responsible for dystocia by causing conditions such as malpresentation or malposition of the fetus, premature rupture of the fetal membranes, and uterine inertia. The cause of pelvic deformities may be congenital (rare) or acquired from disease, poor posture, or fractures caused by injury. Pelvic deformities are more common in women who have grown up in a poor environment and are undernourished. It is probable that these women suffered in their youth from minor degrees of rickets. In 1933, Caldwell and Moloy classified pelves into four groups: gynecoid, android, anthropoid, and platypelloid (Fig. 6-5C). The gynecoid type, present in about 41% of women, is the typical female pelvis, which was previously described. The android type, present in about 33% of white females and 16% of black females, is the male or funnel-shaped pelvis with a contracted outlet. The anthropoid type, present in about 24% of white females and 41% of black females, is long, narrow, and oval shaped. The platypelloid type, present in only about 2% of women, is a wide pelvis flattened at the brim, with the promontory of the sacrum pushed forward. P.312
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Figure 6-4 Pelvic inlet, pelvic outlet, diagonal conjugate, and axis of the pelvis. Some of the main differences between the female and the male pelvis are also shown.

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Figure 6-5 A. Birth canal. Interrupted line indicates the axis of the canal. B. Procedure used in measuring the diagonal conjugate. C. Different types of pelvic inlets, according to Caldwell and Moloy. D. Estimation of the width of the pelvic outlet by means of a closed fist.

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Figure 6-6 Right half of the pelvis showing the pelvic walls.

The sacrum is usually wider in proportion to its length in the female than in the male. The sacrum is tilted forward so that it forms an angle with the fifth lumbar vertebra, called the lumbosacral angle. Coccyx The coccyx consists of four vertebrae fused together to form a small triangular bone, which articulates at its base with the lower end of the sacrum (Fig. 6-8).

Figure 6-7 Anterior wall of the pelvis (posterior view).

The coccygeal vertebrae consist of bodies only, but the first vertebra possesses a rudimentary transverse process and cornua. The cornua are the remains of the pedicles and superior articular processes and project upward to articulate with the sacral cornua (Fig. 6-8). Piriformis Muscle The piriformis muscle arises from the front of the lateral mass of the sacrum and leaves the pelvis to enter the gluteal P.316
region by passing laterally through the greater sciatic foramen (Fig. 6-9). It is inserted into the upper border of the greater trochanter of the femur.

Figure 6-8 Sacrum. A. Anterior view. B. Posterior view.
  • Action: It is a lateral rotator of the femur at the hip joint.
  • Nerve supply: It receives branches from the sacral plexus.

Lateral Pelvic Wall The lateral pelvic wall is formed by part of the hip bone below the pelvic inlet, the obturator membrane, the sacrotuberous and sacrospinous ligaments, and the obturator internus muscle and its covering fascia. Hip Bone In children, each hip bone consists of the ilium, which lies superiorly; the ischium, which lies posteriorly and inferiorly; and the pubis, which lies anteriorly and inferiorly (Fig. 6-3). The three separate bones are joined by cartilage at the acetabulum. At puberty, these three bones fuse together to form one large, irregular bone. The hip bones articulate with the sacrum at the sacroiliac joints and form the anterolateral P.317
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walls of the pelvis; they also articulate with one another anteriorly at the symphysis pubis.

Figure 6-9 Posterior wall of the pelvis.
Figure 6-10 Sacrum from behind. Laminae have been removed to show the sacral nerve roots lying within the sacral canal. Note that in the adult the spinal cord ends below, at the level of the lower border of the first lumbar vertebra.

On the outer surface of the hip bone is a deep depression, the acetabulum, which articulates with the hemispherical head of the femur (Figs. 6-1 and 6-3). Behind the acetabulum is a large notch, the greater sciatic notch, which is separated from the lesser sciatic notch by the spine of the ischium. The sciatic notches are converted into the greater and lesser sciatic foramina by the presence of the sacrotuberous and sacrospinous ligaments (Fig. 6-2). The ilium, which is the upper flattened part of the hip bone, possesses the iliac crest (Fig. 6-3). The iliac crest runs between the anterior and posterior superior iliac spines. Below these spines are the corresponding anterior and posterior inferior iliac spines. On the inner surface of the ilium is the large auricular surface for articulation with the sacrum. The iliopectineal line runs downward and forward around the inner surface of the ilium and serves to divide the false from the true pelvis. The ischium is the inferior and posterior part of the hip bone and possesses an ischial spine and an ischial tuberosity (Fig. 6-3). The pubis is the anterior part of the hip bone and has a body and superior and inferior pubic rami. The body of the pubis bears the pubic crest and the pubic tubercle and articulates with the pubic bone of the opposite side at the symphysis pubis (Fig. 6-1). In the lower part of the hip bone is a large opening, the obturator foramen, which is bounded by the parts of the ischium and pubis. The obturator foramen is filled in by the obturator membrane (Fig. 6-3). Obturator Membrane The obturator membrane is a fibrous sheet that almost completely closes the obturator foramen, leaving a small gap, the obturator canal, for the passage of the obturator nerve and vessels as they leave the pelvis to enter the thigh (Fig. 6-3). Sacrotuberous Ligament The sacrotuberous ligament is strong and extends from the lateral part of the sacrum and coccyx and the posterior inferior iliac spine to the ischial tuberosity (Figs. 6-2 and 6-9). Sacrospinous Ligament The sacrospinous ligament is strong and triangle shaped. It is attached by its base to the lateral part of the sacrum and coccyx and by its apex to the spine of the ischium (Figs. 6-2 and 6-9). The sacrotuberous and sacrospinous ligaments prevent the lower end of the sacrum and the coccyx from being rotated upward at the sacroiliac joint by the weight of the body (Fig. 6-11). The two ligaments also convert the greater and lesser sciatic notches into foramina, the greater and lesser sciatic foramina. Obturator Internus Muscle The obturator internus muscle arises from the pelvic surface of the obturator membrane and the adjoining part of the hip bone (Fig. 6-12). The muscle fibers converge to a tendon, which leaves the pelvis through the lesser sciatic foramen and is inserted into the greater trochanter of the femur.

  • Action: It laterally rotates the femur at the hip joint.
  • Nerve supply: The nerve to the obturator internus, a branch from the sacral plexus

Inferior Pelvic Wall, or Pelvic Floor The floor of the pelvis supports the pelvic viscera and is formed by the pelvic diaphragm. The pelvic floor stretches across the pelvis and divides it into the main pelvic cavity above, which contains the pelvic viscera, and the perineum below. The perineum is considered in detail in Chapter 8. Pelvic Diaphragm The pelvic diaphragm is formed by the important levatores ani muscles and the small coccygeus muscles and their covering fasciae (Fig. 6-13). It is incomplete anteriorly to allow passage of the urethra in males and the urethra and the vagina in females. Levator Ani Muscle The levator ani muscle is a wide thin sheet that has a linear origin from the back of the body of the pubis, a tendinous arch formed by a thickening of the fascia covering the obturator internus, and the spine of the ischium (Fig. 6-13). From this extensive origin, groups of fibers sweep downward and medially to their insertion (Fig. 6-14), as follows:

  • Anterior fibers: The levator prostatae or sphincter vaginae form a sling around the prostate or vagina and are inserted into a mass of fibrous tissue, called the perineal body, in front of the anal canal. The levator prostatae support the prostate and stabilize the perineal body. The sphincter vaginae constrict the vagina and stabilize the perineal body.
  • Intermediate fibers: The puborectalis forms a sling around the junction of the rectum and anal canal. The pubococcygeus passes posteriorly to be inserted into a small fibrous mass, called the anococcygeal body, between the tip of the coccyx and the anal canal.
  • Posterior fibers: The iliococcygeus is inserted into the anococcygeal body and the coccyx.
  • Action: The levatores ani muscles of the two sides form an efficient muscular sling that supports and maintains the pelvic viscera in position. They resist the rise in intrapelvic pressure during the straining and expulsive efforts of the abdominal muscles (as occurs in coughing). They also have an important sphincter action on the anorectal junction, and in the female they serve also as a sphincter of the vagina.
  • Nerve supply: The perineal branch of the fourth sacral nerve and from the perineal branch of the pudendal nerve

Coccygeus Muscle This small triangular muscle arises from the spine of the ischium and is inserted into the lower end of the sacrum and into the coccyx (Figs. 6-13 and 6-14).

  • Action: The two muscles assist the levatores ani in supporting the pelvic viscera. P.319
    Figure 6-11 Horizontal section through the pelvis showing the sacroiliac joints and the symphysis pubis. The lower diagram shows the function of the sacrotuberous and sacrospinous ligaments in resisting the rotation force exerted on the sacrum by the weight of the trunk.
  • Nerve supply: A branch of the fourth and fifth sacral nerves

A summary of the attachments of the muscles of the pelvic walls and floor, their nerve supply, and their action is given in Table 6-1. Pelvic Fascia The pelvic fascia is formed of connective tissue and is continuous above with the fascia lining the abdominal walls. Below, the fascia is continuous with the fascia of the perineum. The pelvic fascia can be divided into parietal and visceral layers. Parietal Pelvic Fascia The parietal pelvic fascia lines the walls of the pelvis and is named according to the muscle it overlies (Fig. 6-17). Where the pelvic diaphragm is deficient anteriorly, the parietal pelvic fascia becomes continuous through the opening with the fascia covering the inferior surface of the pelvic diaphragm, in the perineum. It covers the sphincter urethrae muscle and the perineal membrane (see page 401) P.320
and forms the superior fascial layer of the urogenital diaphragm.

Figure 6-12 Lateral wall of the pelvis.
Figure 6-13 Inferior wall or floor of the pelvis.

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Figure 6-14 Levator ani muscle and coccygeus muscle seen on their inferior aspects. Note that the levator ani is made up of several different muscle groups. The levator ani and coccygeus muscles with their fascial coverings form a continuous muscular floor to the pelvis, known as the pelvic diaphragm.

Visceral Layer of Pelvic Fascia The visceral layer of pelvic fascia covers and supports all the pelvic viscera. In certain locations the fascia thickens and extends from the viscus to the pelvic walls and provides support. These fascial ligaments are named according to their attachments, for example, the pubovesical and the sacrocervical ligaments. Clinical Notes Fascial Ligaments of the Uterine Cervix In the female the fascial ligaments attached to the uterine cervix are of particular clinical importance because they assist with the support of the uterus and thus prevent uterine prolapse (see page 366). The visceral pelvic fascia around the uterine cervix and vagina is commonly referred to as the parametrium. Pelvic Peritoneum The parietal peritoneum lines the pelvic walls and is reflected onto the pelvic viscera and becomes continuous with the visceral peritoneum (Fig. 6-17). For further details, see pages 356 to 376. Clinical Notes Fractures of the Pelvis Fractures of the False Pelvis Fractures of the false pelvis caused by direct trauma occasionally occur. The upper part of the ilium is seldom displaced because of the attachment of the iliacus muscle on the inside and the gluteal muscles on the outside. Fractures of the True Pelvis The mechanism of fractures of the true pelvis can be better understood if the pelvis is regarded not only as a basin but also as a rigid ring (Fig. 6-15). The ring is made up of the pubic rami, the ischium, the acetabulum, the ilium, and the sacrum, joined by strong ligaments at the sacroiliac and symphyseal joints. If the ring breaks at any one point, the fracture will be stable and no displacement will occur. However, if two breaks occur in the ring, the fracture will be unstable and displacement will occur, because the postvertebral and abdominal muscles will shorten and elevate the lateral part of the pelvis (Fig. 6-15). The break in the ring may occur not as the result of a fracture but as the result of disruption of the sacroiliac or symphyseal joints. Fracture of bone on either side of the joint is more common than disruption of the joint. The forces responsible for the disruption of the bony ring may be anteroposterior compression, lateral compression, or shearing. A heavy fall on the greater trochanter of the femur may drive the head of the femur through the floor of the acetabulum into the pelvic cavity. Fractures of the Sacrum and Coccyx Fractures of the lateral mass of the sacrum may occur as part of a pelvic fracture. Fractures of the coccyx are rare. However, coccydynia is common and is usually caused by direct trauma to the coccyx, as in falling down a flight of concrete steps. The anterior surface of the coccyx can be palpated with a rectal examination. Minor Fractures of the Pelvis The anterior superior iliac spine may be pulled off by the forcible contraction of the sartorius muscle in athletes (Fig. 6-15). In a similar manner the anterior inferior iliac spine may be avulsed by the contraction of the rectus femoris muscle (origin of the straight head). The ischial tuberosity can be avulsed by the contraction of the hamstring muscles. Healing may occur by fibrous union, possibly resulting in elongation of the muscle unit and some reduction in muscular efficiency. Anatomy of Complications of Pelvic Fractures Fractures of the true pelvis are commonly associated with injuries to the soft pelvic tissues. If damaged, the thin pelvic veins—namely, the internal iliac veins and their tributaries—that lie in the parietal pelvic fascia beneath the parietal peritoneum can be the source of a massive hemorrhage, which may be life threatening. The male urethra is often damaged, especially in vertical shear fractures that may disrupt the urogenital diaphragm (see page 407). The bladder, which lies immediately behind the pubis in both sexes, is occasionally damaged by spicules of bone; a full bladder is more likely to be injured than an empty bladder (see page 353). The rectum lies within the concavity of the sacrum and is protected and rarely damaged. Fractures of the sacrum or ischial spine may be thrust into the pelvic cavity, tearing the rectum. Nerve injuries can follow sacral fractures; the laying down of fibrous tissue around the anterior or posterior nerve roots or the branches of the sacral spinal nerves can result in persistent pain. Damage to the sciatic nerve may occur in fractures involving the boundaries of the greater sciatic notch. The peroneal part of the sciatic nerve is most often involved, resulting in the inability of a conscious patient to dorsiflex the ankle joint or failure of an unconscious patient to reflexly plantar-flex (ankle jerk) the foot (see page 659). Pelvic Floor The pelvic diaphragm is a gutter-shaped sheet of muscle formed by the levatores ani and coccygeus muscles and their covering fasciae. From their origin, the muscle fibers on the two sides slope downward and backward to the midline, producing a gutter that slopes downward and forward. A rise in the intra-abdominal pressure, caused by the contraction of the diaphragm and the muscles of the anterior and lateral abdominal walls, is counteracted by the contraction of the muscles forming the pelvic floor. By this means, the pelvic viscera are supported and do not “drop out” through the pelvic outlet. Contraction of the puborectalis fibers greatly assists the anal sphincters in maintaining continence under these conditions by pulling the anorectal junction upward and forward. During the act of defecation, however, the levator ani continues to support the pelvic viscera but the puborectalis fibers relax with the anal sphincters. Functional Significance of the Pelvic Floor in the Female The female pelvic floor serves an important function during the second stage of labor (Fig. 6-16). At the pelvic inlet, the widest diameter is transverse so that the longest axis of the baby’s head (anteroposterior) takes up the transverse position. When the head reaches the pelvic floor, the gutter shape of the floor tends to cause the baby’s head to rotate so that its long axis comes to lie in the anteroposterior position. The occipital part of the head now moves downward and forward along the gutter until it lies under the pubic arch. As the baby’s head passes through the lower part of the birth canal, the small gap that exists in the anterior part of the pelvic diaphragm becomes enormously enlarged so that the head may slip through into the perineum. Once the baby has passed through the perineum, the levatores ani muscles recoil and take up their previous position. Injury to the Pelvic Floor Injury to the pelvic floor during a difficult childbirth can result in the loss of support for the pelvic viscera leading to uterine and vaginal prolapse, herniation of the bladder (cystocele), and alteration in the position of the bladder neck and urethra, leading to stress incontinence. In the latter condition, the patient dribbles urine whenever the intra-abdominal pressure is raised, as in coughing. Prolapse of the rectum may also occur. Partial Fusion of the Sacral Vertebrae The first sacral vertebra can be partly or completely separated from the second sacral vertebra. Occasionally, on radiographs of the vertebral column, examples are seen in which the fifth lumbar vertebra has fused with the first sacral vertebra. Trauma to the True Pelvis Trauma to the true pelvis can result in fracture of the lateral mass of the sacrum (see previous column). P.322
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Figure 6-15 A–C. Different types of fractures of the pelvic basin. D. Avulsion fractures of the pelvis. The sartorius muscle is responsible for the avulsion of the anterior superior iliac spine; the straight head of the rectus femoris muscle, for the avulsion of the anterior inferior iliac spine; and the hamstring muscles, for the avulsion of the ischial tuberosity.
Figure 6-16 Stages in rotation of the baby’s head during the second stage of labor. The shape of the pelvic floor plays an important part in this process.

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Table 6-1 Muscles of the Pelvic Walls and Floor
Name of Muscle Origin Insertion Nerve Supply Action
Piriformis Front of sacrum Greater trochanter of femur Sacral plexus Lateral rotator of femur at hip joint
Obturator internus Obturator membrane and adjoining part of hip bone Greater trochanter of femur Nerve to obturator internus from sacral plexus Lateral rotator of femur at hip joint
Levator ani Body of pubis, fascia of obturator internus, spine of ischium Perineal body; anococcygeal body; walls of prostate, vagina, rectum, and anal canal Fourth sacral nerve, pudendal nerve Supports pelvic viscera; sphincter to anorectal junction and vagina
Coccygeus Spine of ischium Lower end of sacrum; coccyx Fourth and fifth sacral nerve Assists levator ani to support pelvic viscera; flexes coccyx
Figure 6-17 Coronal section through the pelvis.

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Figure 6-18 Posterior pelvic wall showing the sacral plexus, superior hypogastric plexus, and right and left inferior hypogastric plexuses. Pelvic parts of the sympathetic trunks are also shown.

Nerves of the Pelvis Sacral Plexus The sacral plexus lies on the posterior pelvic wall in front of the piriformis muscle (Fig. 6-18). It is formed from the anterior rami of the fourth and fifth lumbar nerves and the anterior rami of the first, second, third, and fourth sacral nerves (Fig. 6-19). The fourth lumbar nerve joins the fifth lumbar nerve to form the lumbosacral trunk. The lumbosacral trunk passes down into the pelvis and joins the sacral nerves as they emerge from the anterior sacral foramina. Relations

  • Anteriorly: The internal iliac vessels and their branches, and the rectum (Fig. 6-12)
  • Posteriorly: The piriformis muscle (Fig. 6-18)

Branches

  • Branches to the lower limb that leave the pelvis through the greater sciatic foramen (Fig. 6-12):
  • The sciatic nerve (L4 and 5; S1, 2, and 3), the largest branch of the plexus and the largest nerve in the body (Fig. 6-9)
  • The superior gluteal nerve, which supplies the gluteus medius and minimus and the tensor fasciae latae muscles
  • The inferior gluteal nerve, which supplies the gluteus maximus muscle
  • The nerve to the quadratus femoris muscle, which also supplies the inferior gemellus muscle
  • The nerve to the obturator internus muscle, which also supplies the superior gemellus muscle
  • The posterior cutaneous nerve of the thigh, which supplies the skin of the buttock and the back of the thigh
  • Branches to the pelvic muscles, pelvic viscera, and perineum:
  • The pudendal nerve (S2, 3, and 4), which leaves the pelvis through the greater sciatic foramen and enters the perineum through the lesser sciatic foramen (Fig. 6-12)
  • The nerves to the piriformis muscle
  • The pelvic splanchnic nerves, which constitute the sacral part of the parasympathetic system and arise from the second, third, and fourth sacral nerves. They are distributed to the pelvic viscera.
  • The perforating cutaneous nerve, which supplies the skin of the lower medial part of the buttock

The branches of the sacral plexus and their distribution are summarized in Table 6-2. Clinical Notes Sacral Plexus Pressure from the Fetal Head During the later stages of pregnancy, when the fetal head has descended into the pelvis, the mother often complains of discomfort or aching pain extending down one of the lower limbs. The discomfort, caused by pressure from the fetal head, is often relieved by changing position, such as lying on the side in bed. Invasion by Malignant Tumors The nerves of the sacral plexus can become invaded by malignant tumors extending from neighboring viscera. A carcinoma of the rectum, for example, can cause severe intractable pain down the lower limbs. Referred Pain from the Obturator Nerve The obturator nerve lies on the lateral wall of the pelvis and supplies the parietal peritoneum. An inflamed appendix hanging down into the pelvic cavity could cause irritation of the obturator nerve endings, leading to referred pain down the inner side of the right thigh. Inflammation of the ovaries can produce similar symptoms. Caudal Anesthesia (Analgesia) Anesthetic solutions can be injected into the sacral canal through the sacral hiatus. The solutions then act on the spinal roots of the second, third, fourth, and fifth sacral and coccygeal segments of the cord as they emerge from the dura mater. The roots of higher spinal segments can also be blocked by this method. The needle must be confined to the lower part of the sacral canal, because the meninges extend down as far as the lower border of the second sacral vertebra. Caudal anesthesia is used in obstetrics to block pain fibers from the cervix of the uterus and to anesthetize the perineum. P.326
Branches of the Lumbar Plexus Lumbosacral Trunk Part of the anterior ramus of the fourth lumbar nerve emerges from the medial border of the psoas muscle and joins the anterior ramus of the fifth lumbar nerve to form the lumbosacral trunk (Figs. 6-18 and 6-19). This trunk now enters the pelvis by passing down in front of the sacroiliac joint and joins the sacral plexus.

Figure 6-19 Sacral plexus.

Obturator Nerve The obturator nerve is a branch of the lumbar plexus (L2, 3, and 4), emerges from the medial border of the psoas muscle in the abdomen, and accompanies the lumbosacral trunk down into the pelvis. It crosses the front of the sacroiliac joint and runs forward on the lateral pelvic wall in the angle between the internal and external iliac vessels (Fig. 6-12). On reaching the obturator canal (that is, the upper part of the obturator foramen, which is devoid of the obturator P.327
membrane), it splits into anterior and posterior divisions that pass through the canal to enter the adductor region of the thigh. The distribution of the obturator nerve in the thigh is considered on page 586.

Table 6-2 Branches of the Sacral Plexus and Their Distribution
Branches Distribution
Superior gluteal nerve Gluteus medius, gluteus minimus, and tensor fasciae latae muscles
Inferior gluteal nerve Gluteus maximus muscle
Nerve to piriformis Piriformis muscle
Nerve to obturator internus Obturator internus and superior gemellus muscles
Nerve to quadratus femoris Quadratus femoris and inferior gemellus muscles
Perforating cutaneous nerve Skin over medial aspect of buttock
Posterior cutaneous nerve of thigh Skin over posterior surface of thigh and popliteal fossa, also over lower part of buttock, scrotum, or labium majus
Sciatic nerve (L4, 5; S1, 2, 3) Tibial portion Hamstring muscles (semitendinosus, biceps femoris [long head], adductor magnus [hamstring part]), gastrocnemius, soleus, plantaris, popliteus, tibialis posterior, flexor digitorum longus, flexor hallucis longus, and via medial and lateral plantar branches to muscles of sole of foot; sural branch supplies skin on lateral side of leg and foot
    Common peroneal portion Biceps femoris muscle (short head) and via deep peroneal branch: tibialis anterior, extensor hallucis longus, extensor digitorum longus, peroneus tertius, and extensor digitorum brevis muscles; skin over cleft between first and second toes. The superficial peroneal branch supplies the peroneus longus and brevis muscles and skin over lower third of anterior surface of leg and dorsum of foot
    Pudendal nerve Muscles of perineum including the external anal sphincter, mucous membrane of lower half of anal canal, perianal skin, skin of penis, scrotum, clitoris, and labia majora and minora

Branches Sensory branches supply the parietal peritoneum on the lateral wall of the pelvis. Autonomic Nerves Pelvic Part of the Sympathetic Trunk The pelvic part of the sympathetic trunk is continuous above, behind the common iliac vessels, with the abdominal part (Fig. 6-18). It runs down behind the rectum on the front of the sacrum, medial to the anterior sacral foramina. The sympathetic trunk has four or five segmentally arranged ganglia. Below, the two trunks converge and finally unite in front of the coccyx. Branches

  • Gray rami communicantes to the sacral and coccygeal nerves
  • Fibers that join the hypogastric plexuses

Pelvic Splanchnic Nerves The pelvic splanchnic nerves form the parasympathetic part of the autonomic nervous system in the pelvis. The preganglionic fibers arise from the second, third, and fourth sacral nerves and synapse in ganglia in the inferior hypogastric plexus or in the walls of the viscera. Some of the parasympathetic fibers ascend through the hypogastric plexuses and thence via the aortic plexus to the inferior mesenteric plexus. The fibers are then distributed along branches of the inferior mesenteric artery to supply the large bowel from the left colic flexure to the upper half of the anal canal. Superior Hypogastric Plexus The superior hypogastric plexus is situated in front of the promontory of the sacrum (Fig. 6-18). It is formed as a continuation of the aortic plexus and from branches of the third and fourth lumbar sympathetic ganglia. It contains sympathetic and sacral parasympathetic nerve fibers and visceral afferent nerve fibers. The superior hypogastric plexus divides inferiorly to form the right and left hypogastric nerves. Inferior Hypogastric Plexuses The inferior hypogastric plexuses lie on each side of the rectum, the base of the bladder, and the vagina (Fig. 6-18). Each plexus is formed from a hypogastric nerve (from the superior hypogastric plexus) and from the pelvic splanchnic nerve. It contains postganglionic sympathetic fibers, preganglionic and postganglionic parasympathetic fibers, and visceral afferent fibers. Branches pass to the pelvic viscera via small subsidiary plexuses. Arteries of the Pelvis Common Iliac Artery Each common iliac artery ends at the pelvic inlet in front of the sacroiliac joint by dividing into the external and internal iliac arteries (Figs. 6-12 and 6-18). P.328
External Iliac Artery The external iliac artery runs along the medial border of the psoas muscle, following the pelvic brim (Fig. 6-12), and gives off the inferior epigastric and deep circumflex iliac branches. It leaves the false pelvis by passing under the inguinal ligament to become the femoral artery. Arteries of the True Pelvis The following arteries enter the pelvic cavity:

  • Internal iliac artery
  • Superior rectal artery
  • Ovarian artery
  • Median sacral artery

Internal Iliac Artery The internal iliac artery passes down into the pelvis to the upper margin of the greater sciatic foramen, where it divides into anterior and posterior divisions (Fig. 6-12). The branches of these divisions supply the pelvic viscera, the perineum, the pelvic walls, and the buttocks. The origin of the terminal branches is subject to variation, but the usual arrangement is shown in Diagram 6-1. Branches of the Anterior Division

  • Umbilical artery: From the proximal patent part of the umbilical artery arises the superior vesical artery, which supplies the upper portion of the bladder (Fig. 6-12).
  • Obturator artery: This artery runs forward along the lateral wall of the pelvis with the obturator nerve and leaves the pelvis through the obturator canal.
  • Inferior vesical artery: This artery supplies the base of the bladder and the prostate and seminal vesicles in the male; it also gives off the artery to the vas deferens.
  • Middle rectal artery: Commonly, this artery arises with the inferior vesical artery (Fig. 6-12). It supplies the muscle of the lower rectum and anastomoses with the superior rectal and inferior rectal arteries.
  • Internal pudendal artery: This artery leaves the pelvis through the greater sciatic foramen and enters the gluteal region below the piriformis muscle (Fig. 6-12). It then enters the perineum by passing through the lesser sciatic foramen and passes forward in the pudendal canal with the pudendal nerve. Its branches supply the musculature of the anal canal and the skin and muscles of the perineum.
    Diagram 6-1 Branches of the Internal Iliac Artery
  • Inferior gluteal artery: This artery leaves the pelvis through the greater sciatic foramen below the piriformis muscle (Fig. 6-12). It passes between the first and second or second and third sacral nerves.
  • Uterine artery: This artery runs medially on the floor of the pelvis and crosses the ureter superiorly (see Fig. 7-28). It passes above the lateral fornix of the vagina to reach the uterus. Here, it ascends between the layers of the broad ligament along the lateral margin of the uterus. It ends by following the uterine tube laterally, where it anastomoses with the ovarian artery. The uterine artery gives off a vaginal branch.
  • Vaginal artery: This artery usually takes the place of the inferior vesical artery present in the male. It supplies the vagina and the base of the bladder.

Branches of the Posterior Division

  • Iliolumbar artery: This artery ascends across the pelvic inlet posterior to the external iliac vessels, psoas, and iliacus muscles.
  • Lateral sacral arteries: These arteries descend in front of the sacral plexus, giving off branches to neighboring structures (Fig. 6-12).
  • Superior gluteal artery: This artery leaves the pelvis through the greater sciatic foramen above the piriformis muscle. It supplies the gluteal region.

Superior Rectal Artery The superior rectal artery is a direct continuation of the inferior mesenteric artery. The name changes as the latter artery crosses the common iliac artery. It supplies the mucous membrane of the rectum and the upper half of the anal canal. Ovarian Artery (The testicular artery enters the inguinal canal and does not enter the pelvis.) The ovarian artery arises from the P.329
abdominal part of the aorta at the level of the first lumbar vertebra. The artery is long and slender and passes downward and laterally behind the peritoneum. It crosses the external iliac artery at the pelvic inlet and enters the suspensory ligament of the ovary. It then passes into the broad ligament and enters the ovary by way of the mesovarium. Median Sacral Artery The median sacral artery is a small artery that arises at the bifurcation of the aorta (Fig. 6-18). It descends over the anterior surface of the sacrum and coccyx. The distribution of the visceral branches of the pelvic arteries is discussed in detail with the individual viscera in Chapter 7. Veins of the Pelvis External Iliac Vein The external iliac vein begins behind the inguinal ligament as a continuation of the femoral vein. It runs along the medial side of the corresponding artery and joins the internal iliac vein to form the common iliac vein (Fig. 6-12). It receives the inferior epigastric and deep circumflex iliac veins. Internal Iliac Vein The internal iliac vein begins by the joining together of tributaries that correspond to the branches of the internal iliac artery. It passes upward in front of the sacroiliac joint and joins the external iliac vein to form the common iliac vein (Fig. 6-12). Median Sacral Veins The median sacral veins accompany the corresponding artery and end by joining the left common iliac vein. Lymphatics of the Pelvis The lymph nodes and vessels are arranged in a chain along the main blood vessels. The nodes are named after the blood vessels with which they are associated. Thus, there are external iliac nodes, internal iliac nodes, and common iliac nodes. Joints of the Pelvis Sacroiliac Joints The sacroiliac joints are strong synovial joints and are formed between the auricular surfaces of the sacrum and the iliac bones (Fig. 6-11). The sacrum carries the weight of the trunk, and, apart from the interlocking of the irregular articular surfaces, the shape of the bones contributes little to the stability of the joints. The strong posterior and interosseous sacroiliac ligaments suspend the sacrum between the two iliac bones. The anterior sacroiliac ligament is thin and lies in front of the joint. The weight of the trunk tends to thrust the upper end of the sacrum downward and rotate the lower end of the bone upward (Fig. 6-11). This rotatory movement is prevented by the strong sacrotuberous and sacrospinous ligaments described previously. The iliolumbar ligament connects the tip of the fifth lumbar transverse process to the iliac crest. Movements A small but limited amount of movement is possible at these joints. In older people, the synovial cavity disappears and the joint becomes fibrosed. Their primary function is to transmit the weight of the body from the vertebral column to the bony pelvis. Nerve Supply The nerve supply is from branches of the sacral spinal nerves. Symphysis Pubis The symphysis pubis is a cartilaginous joint between the two pubic bones (Fig. 6-11). The articular surfaces are covered by a layer of hyaline cartilage and are connected together by a fibrocartilaginous disc. The joint is surrounded by ligaments that extend from one pubic bone to the other. Movements Almost no movement is possible at this joint. Sacrococcygeal Joint The sacrococcygeal joint is a cartilaginous joint between the bodies of the last sacral vertebra and the first coccygeal vertebra. The cornua of the sacrum and coccyx are joined by ligaments. Movements Extensive flexion and extension are possible at this joint. Clinical Notes Pelvic Joints Changes with Pregnancy During pregnancy, the symphysis pubis and the ligaments of the sacroiliac and sacrococcygeal joints undergo softening in response to hormones, thus increasing the mobility and increasing the potential size of the pelvis during childbirth. The hormones responsible are estrogen and progesterone produced by the ovary and the placenta. An additional hormone, called relaxin, produced by these organs can also have a relaxing effect on the pelvic ligaments. Changes with Age Obliteration of the cavity in the sacroiliac joint occurs in both sexes after middle age. Sacroiliac Joint Disease The sacroiliac joint is innervated by the lower lumbar and sacral nerves so that disease in the joint can produce low back pain and pain referred along the sciatic nerve (sciatica). The sacroiliac joint is inaccessible to clinical examination. However, a small area located just medial to and below the posterior superior iliac spine is where the joint comes closest to the surface. In disease of the lumbosacral region, movements of the vertebral column in any direction cause pain in the lumbosacral part of the column. In sacroiliac disease, pain is extreme on rotation of the vertebral column and is worst at the end of forward flexion. The latter movement causes pain because the hamstring muscles (see page 587) hold the hip bones in position while the sacrum is rotating forward as the vertebral column is flexed. P.330
Sex Differences of the Pelvis The sex differences of the bony pelvis are easily recognized. The more obvious differences result from the adaptation of the female pelvis for childbearing. The stronger muscles in the male are responsible for the thicker bones and more prominent bony markings (Figs. 6-1 and 6-4).

  • The false pelvis is shallow in the female and deep in the male.
  • The pelvic inlet is transversely oval in the female but heart shaped in the male because of the indentation produced by the promontory of the sacrum in the male.
  • The pelvic cavity is roomier in the female than in the male, and the distance between the inlet and the outlet is much shorter.
  • The pelvic outlet is larger in the female than in the male. In the female the ischial tuberosities are everted and in the male they are turned in.
  • The sacrum is shorter, wider, and flatter in the female than in the male.
  • The subpubic angle, or pubic arch, is more rounded and wider in the female than in the male.

Radiographic Anatomy Radiographic anatomy of the pelvis is fully described on page 377. Surface Anatomy Surface Landmarks Iliac Crest The iliac crest can be felt through the skin along its entire length (Figs. 6-20, 6-21, and 6-22). Anterior Superior Iliac Spine The anterior superior iliac spine is situated at the anterior end of the iliac crest and lies at the upper lateral end of the fold of the groin (Figs. 6-20, 6-21, and 6-22). Posterior Superior Iliac Spine The posterior superior iliac spine is situated at the posterior end of the iliac crest (Fig. 6-22). It lies at the bottom of a small skin dimple and on a level with the second sacral spine, which coincides with the lower limit of the subarachnoid space; it also coincides with the level of the middle of the sacroiliac joint. Pubic Tubercle The pubic tubercle can be felt on the upper border of the pubis (Figs. 6-20, 6-21, and 6-22). Attached to it is the medial end of the inguinal ligament. The tubercle can be palpated easily in the male by invaginating the scrotum from below with the examining finger. In the female, the pubic tubercle can be palpated through the lateral margin of the labium majus. Pubic Crest The pubic crest is the ridge of bone on the superior surface of the pubic bone, medial to the pubic tubercle (Figs. 6-1 and 6-22). Symphysis Pubis The symphysis pubis (Figs. 6-1 and 6-22) lies in the midline between the bodies of the pubic bones and can be palpated as a solid structure through the fat that is present in this region. Spinous Processes of Sacrum The spinous processes of the sacrum (Fig. 6-22) are fused with each other in the midline to form the median sacral crest. The crest can be felt beneath the skin in the uppermost part of the cleft between the buttocks. Sacral Hiatus The sacral hiatus is situated on the posterior aspect of the lower end of the sacrum, where the extradural space terminates (Fig. 6-22). The hiatus lies about 2 in. (5 cm) above the tip of the coccyx and beneath the skin of the cleft between the buttocks. Coccyx The inferior surface and tip of the coccyx (Fig. 6-22) can be palpated in the cleft between the buttocks about 1 in. (2.5 cm) behind the anus. The anterior surface of the coccyx can be palpated with the gloved finger in the anal canal. Viscera Urinary Bladder In adults, the empty bladder is a pelvic organ and lies posterior to the symphysis pubis. As the bladder fills, it rises up out of the pelvis into the abdomen, where it can be palpated through the anterior abdominal wall above the symphysis pubis (Fig. 6-23). The peritoneum covering the distended bladder becomes peeled off from the anterior abdominal wall so that the front of the bladder is in direct contact with the abdominal wall (see page 349). P.331

Figure 6-20 Anterior view of the pelvis of a 27-year-old man.
Figure 6-21 Anterior view of the pelvis of a 29-year-old woman.

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Figure 6-22 Relationship between different parts of the pelvis and the body surface.

In children, until the age of 6 years, the bladder is an abdominal organ even when empty because the capacity of the pelvic cavity is not great enough to contain it. The neck of the bladder lies just below the level of the upper border of the symphysis pubis. Uterus Toward the end of the second month of pregnancy, the fundus of the uterus can be palpated through the lower part of the anterior abdominal wall. With the progressive enlargement of the uterus, the fundus rises above the level of the umbilicus and reaches the region of the xiphoid process by the ninth month of pregnancy (Fig. 6-23). Later, when the presenting part of the fetus, usually the head, descends into the pelvis, the fundus of the uterus descends also. Rectal and Vaginal Examinations as a Means of Palpating the Pelvic Viscera Bimanual rectoabdominal and vaginal–abdominal examinations are extremely valuable methods of palpating the pelvic viscera; they are described in detail on pages 397 and 412. P.333

Figure 6-23 A. Surface anatomy of the empty bladder and the full bladder B. Height of the fundus of the uterus at various months of pregnancy. Note that the peritoneum covering the distended bladder becomes peeled off from the anterior abdominal wall so that the front of the bladder comes to lie in direct contact with the abdominal wall.

Clinical Problem Solving Study the following case histories and select the best answer to the questions following them. A 65-year-old man with a history of prostatic enlargement complained that he could not micturate. The last time that he passed urine had been 6 hours previously. He was found lying on his bed in great distress, clutching his anterior abdominal wall with both hands and pleading for something to be done quickly. On examination, a large ovoid swelling could be palpated through the abdominal wall above the symphysis pubis. 1. In this patient the following statements are correct except which? (a) In the adult, the urinary bladder is a pelvic structure. (b) When the bladder fills the superior wall of the bladder rises out of the pelvis. (c) When the bladder becomes filled it never reaches a level above the umbilicus. (d) The swelling is dull on percussion. (e) Pressure on the swelling exacerbates the symptoms. View Answer1. C. In extreme cases of urethral obstruction in the male, the superior wall of the bladder has been known to reach the costal margin. A 43-year-old woman was operated on in the perineum to drain an ischial rectal abscess. The abscess extended deeply to the region of the anorectal junction. The surgeon, to obtain better drainage, decided to cut the puborectalis muscle. Then, 3 days later, the patient complained of fecal incontinence. 2. The symptoms displayed by this patient could be explained by the following statements except which? (a) Anal continence is maintained by the tone of the internal and external sphincters and the puborectalis muscle. (b) The puborectalis fibers are a part of the levator ani muscle. (c) The puborectalis fibers pass around the anorectal junction. (d) The puborectalis muscle slings the anorectal junction up to the back of the body of the pubis. (e) The puborectalis muscle plays only a minor role in preserving anal continence. View Answer2. E. The puborectalis muscle is one of the most important sphincters of the anal canal. A heavily built, middle-aged man running down a flight of stone steps misjudged the position of one of the steps and fell suddenly onto his buttocks. Following the fall, he complained of severe bruising of the area of the cleft between the buttocks and persistent pain in this area. 3. The following statements concerning this patient are correct except which? (a) The lower end of the vertebral column was traumatized by the stone step. (b) The coccyx can be palpated beneath the skin in the natal cleft. (c) The anterior surface of the coccyx cannot be felt clinically. (d) The coccyx is usually severely bruised or fractured. (e) The pain is felt in the distribution of dermatomes S4 and S5. View Answer3. C. The anterior surface of the coccyx can be palpated with a gloved finger placed in the anal canal. A 28-year-old pregnant woman was very frightened by the thought of going through the pain of childbirth. She asked her obstetrician if it was possible to relieve the pain without having a general anesthetic. She was told that she could have a relatively simple procedure called caudal anesthesia. 4. When performing caudal anesthesia, the syringe needle is inserted into the sacral canal by piercing the following anatomic structures except which? (a) Skin (b) Fascia (c) Ligaments (d) Sacral hiatus (e) Dura mater View Answer4. E. The dura mater extends down in the sacral canal only as far as the lower border of the second sacral vertebra. It lies about 2 in. (50 mm) above the sacral hiatus in the adult. An elderly woman was run over by an automobile as she was crossing the road. Radiographic examination of the pelvis in the emergency department of the local hospital revealed a fracture of the ilium and iliac crest on the left side. 5. The following statements about fractures of the pelvis are correct except which? (a) Fractures of the ilium have little displacement. (b) Displacement is prevented by the presence of the iliacus and the gluteal muscles on the inner and outer surfaces of this bone, respectively. (c) If two fractures occur in the ring forming the true pelvis, the fracture will be unstable and displacement will occur. (d) Fractures of the true pelvis do not cause injury to the pelvic viscera. (e) The postvertebral and abdominal muscles are responsible for elevating the lateral part of the pelvis should two fractures occur. (f) A heavy fall on the greater trochanter of the femur may drive the head of the femur through the floor of the acetabulum and into the pelvic cavity. View Answer5. D. Fractures of the true pelvis are commonly associated with injuries to the soft pelvic viscera, especially the bladder and the urethra. A pregnant woman visited an antenatal clinic. A vaginal examination revealed that the sacral promontory could be easily palpated and that the diagonal conjugate measured less than 4 in. (10 cm). 6. The following statements concerning this examination are correct except which? (a) Normally it is difficult or impossible to feel the sacral promontory by means of a vaginal examination. (b) The normal diagonal conjugate measures about 10 in. (25 cm). (c) This patient’s pelvis was flattened anteroposteriorly, and the sacral promontory projected too far forward. (d) It is likely that this patient would have an obstructed labor. (e) This patient was advised to have a cesarean section. View Answer6. B. The normal diagonal conjugate measures about 5 in. (11.5 cm). P.334
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Review Questions Multiple-Choice Questions Select the best answer for each question. 1. The following statements concerning the pelvis are correct except which? (a) The ilium, ischium, and pubis are three separate bones that fuse together to form the hip bone in the 25th year of life. (b) The platypelloid type of pelvis occurs in about 2% of women. (c) External pelvic measurements have little practical importance in determining whether a disproportion between the size of the fetal head and the size of the pelvic inlet is likely. (d) The pelvic outlet is formed by the symphysis pubis anteriorly, the ischial tuberosities laterally, the sacrotuberous ligaments laterally, and the coccyx posteriorly. (e) The sacrum is shorter, wider, and flatter in the female than in the male. View Answer1. A. At puberty the three separate bones—the ilium, ischium, and pubis—fuse together to form one large irregular bone, the hip bone. 2. The following statements concerning structures that leave the pelvis are correct except which? (a) The sciatic nerve leaves the pelvis through the greater sciatic foramen. (b) The piriformis muscle leaves the pelvis through the greater sciatic foramen. (c) The external iliac artery passes beneath the inguinal ligament to become the femoral artery. (d) The obturator nerve leaves the pelvis through the lesser sciatic foramen. (e) The inferior gluteal artery leaves the pelvis through the greater sciatic foramen. View Answer2. D. The obturator nerve leaves the pelvis through the obturator canal, which is the upper part of the obturator foramen, devoid of the obturator membrane. 3. The following statements concerning the muscles and fascia in the pelvis are correct except which? (a) The levator ani muscle is innervated by the perineal branch of the fourth sacral nerve and from the perineal branch of the pudendal nerve. (b) In the pelvis, the fascia is divided into parietal and visceral layers. (c) The iliococcygeus muscle arises from a thickening of the obturator internus fascia. (d) The pelvic diaphragm is strong and has no openings. (e) The visceral layer of pelvic fascia forms important ligaments that help support the uterus. View Answer3. D. The pelvic diaphragm is a gutter-shaped sheet of muscle formed by the levatores ani and coccygeus muscles and their covering fasciae. Its function is to support the pelvic viscera. The pelvic diaphragm is incomplete anteriorly, forming an opening to allow passage of the urethra in males and the urethra and the vagina in females. 4. The following statements concerning the nerves of the pelvic cavity are correct except which? (a) The inferior hypogastric plexus contains both sympathetic and parasympathetic nerves. (b) The sacral plexus lies behind the rectum. (c) The pelvic part of the sympathetic trunk possesses both white and gray rami communicantes. (d) The superior hypogastric plexus is formed from the aortic sympathetic plexus and branches of the lumbar sympathetic ganglia. (e) The anterior rami of the upper four sacral nerves emerge into the pelvis through the anterior sacral foramina. View Answer4. C. The pelvic part of the sympathetic trunk gives rise to only gray postganglionic nerve fibers, which are distributed to the pelvic viscera and blood vessels. 5. The following statements concerning the bony pelvis are correct except which? (a) When the patient is in the standing position, the anterior superior iliac spines lie vertically above the anterior surface of the symphysis pubis. (b) Very little movement is possible at the sacrococcygeal joint. (c) The false pelvis helps guide the fetus into the true pelvis during labor. (d) The female sex hormones cause a relaxation of the ligaments of the pelvis during pregnancy. (e) Obliteration of the cavity of the sacroiliac joint often occurs in both sexes after middle age. View Answer5. B. The sacrococcygeal joint is a cartilaginous joint and can perform a great deal of movement. 6. The statements concerning the segmental origin of the following nerves are correct except which? (a) The sciatic nerve is derived from the segments L4 and 5 and S1, 2, and 3. (b) The pudendal nerve is derived from the segments L3, 4, and 5. (c) The pelvic splanchnic nerve is derived from the segments S2, 3, and 4. (d) The obturator nerve is derived from the segments L2, 3, and 4. (e) The lumbosacral trunk is derived from the segments L4 and 5. View Answer6. B. The pudendal nerve is a branch of the sacral plexus and is derived from S2, 3, and 4. 7. The statements concerning the origin of the following arteries are correct except which? (a) The superior rectal artery is derived from the inferior mesenteric artery. (b) The ovarian artery is derived from the renal artery. (c) The uterine artery is derived from the internal iliac artery. (d) The middle rectal artery is derived from the internal iliac artery. (e) The superior gluteal artery is derived from the internal iliac artery. View Answer7. B. Both the right and the left ovarian arteries are branches of the abdominal aorta. 8. The statements concerning the motor nerve supply of the muscles of the pelvic walls are correct except which? (a) The sacral nerves or plexus supply the obturator internus muscle. (b) The obturator nerve supplies the piriformis muscle. (c) The sacral nerves, or plexus, supply the iliococcygeus muscle. (d) The sacral nerves, or plexus, supply the coccygeus muscle. (e) The perineal branch of the fourth sacral nerve and the perineal branch of the pudendal nerve supply the levator ani muscle. View Answer8. B. The piriformis muscle receives its motor nerve supply from the sacral plexus. Read the case history and select the best answer to the question following it. A 37-year-old woman was involved in a severe automobile accident in which the car, traveling at high speed, swerved off the road and hit a tree. She was evaluated in the emergency department and found to have multiple injuries. Radiographic examination of her pelvis showed a fracture of her right ilium and iliac crest. 9. From your knowledge of anatomy, determine which of the following treatments was correct. (a) An attempt was made to immobilize the bony fragments by encasing the patient in a plaster cast extending from the subcostal region down both thighs to just above the knee. (b) The right gluteal region was strapped with a strong Elastoplast bandage. (c) The patient was operated on and the bony fragments were replaced in their correct anatomic position and secured with screws. (d) Splinting of the fractured bone was unnecessary. (e) Because of the fear of avascular necrosis, the smaller bony fragments were surgically removed. View Answer9. D. Most fractures of the upper part of the ilium have little displacement of the bone fragments. This is because the iliacus muscle is attached to the inner surface and the gluteal muscles are attached to the outer surface. Splinting the bones is unnecessary because of the attachment of these muscles. The muscular attachments also provide an adequate blood supply to the bone fragments. Footnote *The term pelvis is loosely used to describe the region where the trunk and lower limbs meet. The word pelvis means “a basin” and is more correctly applied to the skeleton of the region—that is, the pelvic girdle or bony pelvis.

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