PELVIC WALLJOINTS OF THE PELVIS

PELVIC FLOOR

PELVIC WALL

Dr. L. Tchakarov 3

• 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

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The bony pelvis provides a strong, stable connection between the trunk and the lower extremities.

The bony pelvis provides a strong, stable connection between the trunk and the lower extremities.

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The main functions of the pelvis are:

1. to transmit the weight of the body from the vertebral column to the femurs;

2. to contain, support, and protect the pelvic viscera; and

3. to provide attachment for trunk and lower limb muscles.

The main functions of the pelvis are:

1. to transmit the weight of the body from the vertebral column to the femurs;

2. to contain, support, and protect the pelvic viscera; and

3. to provide attachment for trunk and lower limb muscles.

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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.

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• 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 with its joints form a strong basin-shaped structure that contains and protects the lower parts of the intestinal and urinary tracts and the internal organs of reproduction.

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• The pelvis is divided into two parts by the pelvic brim. • Above the brim is the false pelvis, which forms part of the

abdominal cavity. • Below the brim is the true pelvis.

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The pelvic brim is formed by: • the sacral promontory (anterior and upper margin of the first

sacral vertebra) behind, • the ileopectineal 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.

ORIENTATION OF THE PELVIS

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• In the standard anatomic position, the front of the symphysis pubis and the anterior superior iliac spines lie in the same vertical plane.

• This means that the pelvic surface of the symphysis pubis faces upward and backward and the anterior surface of the sacrum is directed forward and downward.

FALSE PELVIS

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• The false pelvis 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

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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.

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The true pelvis has:

• an inlet, • an outlet, • and a cavity.

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The pelvic inlet, or pelvic brim, is bounded posteriorly by the sacral promontory, laterally by the iliopectineal lines, and anteriorly by the symphysis pubis.

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The pelvic outlet is bounded:• posteriorly by the coccyx,coccyx, • laterally by the ischial ischial

tuberosities,tuberosities, and • anteriorly by the pubic archpubic arch..

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The pelvic outlet does not present a smooth outline but has three wide notches:

• Anteriorly, the pubic arch is between the ischiopubic rami, and,

• laterally, are the sciatic notches.

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The sciatic notches are divided by the sacrotuberous and sacrospinous ligaments into the greater and lesser sciatic foramina.

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• 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.

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• 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.

Structure of the Pelvic Walls

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• 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.

ANTERIOR PELVIC WALL

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The anterior pelvic wall is the shallowest wall and is formed by the posterior surfaces of the bodies of the pubic bones, the pubic rami, and the symphysis pubis.

POSTERIOR PELVIC WALL

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The posterior pelvic wall is extensive and is formed by the sacrum and coccyx and by the piriformis muscles and their covering of parietal pelvic fascia.

Sacrum

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• The sacrum consists of five rudimentary vertebrae fused together to form a single wedge-shaped bone with a forward concavity.

• The upper border or base of the bone articulates with the fifth lumbar vertebra.

• The narrow inferior border articulates with the coccyx.

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• Laterally, the sacrum articulates with the two iliac bones to form the sacroiliac joints.

• The anterior and upper margins of the first sacral vertebra bulge forward as the posterior margin of the pelvic inlet—the sacral promontory —which is an important obstetric landmark used when measuring the size of the pelvis.

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• 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.sacral hiatus.

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The sacral canal contains the anterior and posterior roots of the lumbar, sacral, and coccygeal spinal nerves; the filum terminale; and fibrofatty material.

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The sacral canal also contains the lower part of the subarachnoid space down as far as the lower border of the second sacral vertebra.

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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.

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The sacrum is usually wider in proportion to its length in the female than in the male.

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The sacrum is tilted forward so that it forms an angle with the fifth lumbar vertebra, called the lumbosacral angle.

Coccyx

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• 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.

• 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.

Piriformis Muscle

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• The piriformis muscle arises from the front of the lateral masses of the sacrum and leaves the pelvis to enter the gluteal region by passing laterally through the greater sciatic foramen.

• It is inserted into the upper border of the greater trochanter of the femur.

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• 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

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• 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

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• 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.

• The three separate bones are joined by cartilage at the acetabulum.

• At puberty, these three bones fuse together to form one large, irregular bone.

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The hip bones articulate with the sacrum at the sacroiliac joints and form the anterolateral walls of the pelvis; they also articulate with one another anteriorly at the symphysis pubis.

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• On the outer surface of the hip bone is a deep depression, the acetabulum, which articulates with the hemispherical head of the femur.

• 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.

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• The sciatic notches are converted into the greater and lesser sciatic foramina

• by the presence of the sacrotuberous and sacrospinous ligaments.

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• The ilium, which is the upper flattened part of the hip bone, possesses the iliac crest.

• The iliac crest runs between the anterior and posterior superior iliac spines.

• Below these spines are the corresponding anterior and posterior inferior iliac spines.

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• 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.

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The ischium is the inferior and posterior part of the hip bone and possesses an ischial spine and an ischial tuberosity.

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• 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.

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• 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.

Obturator Membrane

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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.

Sacrotuberous Ligament

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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.

Sacrospinous Ligament

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• 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.

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• 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.

• The two ligaments also convert the greater and lesser sciatic notches into foramina, the greater and lesser sciatic foramina.

Obturator Internus Muscle

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• The obturator internus muscle arises from the pelvic surface of the obturator membrane and the adjoining part of the hip bone.

• 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.

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• Action: The obturator internus is a lateral rotator of the femur at the hip joint.

• Nerve supply: The muscle is supplied by the nerve to the obturator internus, a branch from the sacral plexus.

INFERIOR PELVIC WALL,

OR PELVIC FLOOR

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• 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.

PELVIC DIAPHRAGM

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It is incomplete anteriorly to allow passage of the urethra in males and the urethra and the vagina in females.

The pelvic diaphragm is formed by the important levatores ani muscles and the small coccygeus muscles and their covering fasciae.

Levator Ani Muscle

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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 archtendinous arch formed by a thickening of the pelvic fascia covering the obturator internus, and the spine of the ischium.

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From this extensive origin, groups of fibers sweep downward and medially to their insertion, as follows:

1. Anterior fibers: • The levator

prostatae or sphincter vaginae form a sling around the prostate or vagina.

levator prostatae

sphincter vaginae

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• They 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.

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2. Intermediate fibers: • The puborectalis forms a sling around

the junction of the rectum and anal canal.

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• The pubococcygeus passes posteriorly to be inserted into a small fibrous mass, called the anococcygeal body,anococcygeal body, between the tip of the coccyx and the anal canal.

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3. Posterior fibers: • The iliococcygeus is inserted

into the anococcygeal bodyanococcygeal body and the coccyx.

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Action: 1. The levatores ani muscles of the two

sides form an efficient muscular sling that supports and maintains the pelvic viscera in position.

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2. They resist the rise in intrapelvic pressure during the straining and expulsive efforts of the abdominal muscles (as occurs in coughing).

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3. They also have an important sphincter action on the anorectal junction, and in the female they serve also as a sphincter of the vagina.

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Nerve supply: This is from the perineal branch of the fourth sacral nerve and from the perineal branch of the pudendal nerve.

Coccygeus Muscle

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• 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.

• Action: The two muscles assist the levatores ani in supporting the pelvic viscera.

• Nerve supply: From a branch of the fourth and fifth sacral nerves.

IN BRIEF…

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Pelvic Fascia

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• 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

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• The parietal pelvic fascia lines the walls of the pelvis and is named according to the muscle it overlies.

• For example, over the obturator internus muscle it is dense and strong and is known as the obturator internus fascia.

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Over the levator ani and coccygeus muscles it forms the levator ani and coccygeus fascia or, to describe it more concisely, the superior fascial layer of the pelvic diaphragm.

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• 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.

• In many locations where the parietal fascia comes into contact with bone it fuses with the periosteum.

• 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.

• In many locations where the parietal fascia comes into contact with bone it fuses with the periosteum.

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Plane of cut

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Below in the perineum, where the parietal pelvic fascia covers the sphincter urethrae muscle and the perineal membrane, it is known as the perineal layer of the parietal pelvic fascia; that is, it forms the superior fascial layer of the urogenital diaphragm.

VISCERAL LAYER OF PELVIC FASCIA

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• In certain locations the fascia thickens to form fascial ligaments, which commonly extend from the pelvic walls to a viscus and provide it with additional support.

• These ligaments are usually named according to their attachments, for example, the pubovesical and the sacrocervical ligaments.

• The visceral layer of pelvic fascia is a layer of loose connective tissue that covers and supports all the pelvic viscera.

• Where a particular viscus comes into contact with the pelvic wall, the visceral layer fuses with the parietal layer.

Pelvic Peritoneum

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The parietal peritoneum lines the pelvic walls and is reflected onto the pelvic viscera, where it becomes continuous with the visceral peritoneum.

MALE V/S FEMALE PELVIS

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• 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.

THE END