Bony pelvis, pelvic walls, and pelvic measurements text_P.pdf

7/27/2019 Bony pelvis, pelvic walls, and pelvic measurements text_P.pdf

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Bony pelvis, pelvic walls, and pelvicmeasurements Dr. Akef Obeida

Objectives

1. Demonstrate knowledge of the gross anatomy of the bony pelvis, pelvic walls, and pelvicmeasurements.

2. Demonstrate knowledge of the gross anatomy of the internal female reproductive organs.3. Recognize and describe the appearance of: The uterus, the cervix, the vagina, the fallopian

tubes, and the ovaries.

Keywords

Bony pelvis Pelvic walls Pelvic diaphragm Female reproductive organs Female genitalia Uterus Cervix Vagina Fallopian tubes Oviduct Ovaries Broad ligaments

Lecture


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The Bony Pelvis

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

It contains, supports, and protects the pelvic viscera.

It is composed of 4 bones:

2 innominate (hip) bones.

Sacrum.

Coccyx.

The two hip bones articulate with each other anteriorly at the symphysis pubis, and posteriorly

with the sacrum at the sacroiliac joints.

Hip Bone (Innominate Bone)

In children, each hip bone consists of the ilium, the ischium, and the pubis.

At puberty, these 3 bones fuse together.

The Ilium

Consists of an upper fan-shaped segment (ala=wing= fossa), and an inferior body. The arcuate line (iliopectineal line) is a curved bony ridge on the interior surface dividing

the iliac fossa from the lower portion of the ilium. It also divides the false from the truepelvis.

The curved upper edge of the ilium is known as iliac crest which runs between anterior andposterior iliac spines.


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Below these spines are the corresponding inferior iliac spines.The Ischium

Consists of:

1. A lower thick, bony process (ischial tuberosity) fusing with the inferior ramus of the pubis(ischiopubic ramus) forming the lower perimeter of the obturator foramen.

2. An upwardly directed bony process that fuses with the ilium and the superior ramus of thepubis, forming part of the upper perimeter of the obturator foramen.

3. The ischial spine protrudes 2-3 cm superior to the ischial tuberosity.4. The lesser sciatic notch: curved bony edge (inwardly) connecting the ischial spine to the

tuberosity.

5. The greater sciatic notch is a similar but a larger curve that extends between the ischialspine and the articular surface of the sacroiliac joint.

N.B. The sciatic notches are converted into the greater and lesser sciatic foramina by the

presence of the sacrotuberous and sacrospinous ligaments.

The pubis

V shaped, with a body (apex pointing medially), and two rami (superior and inferior). The pubic symphysis consists of a fibro- cartilaginous disk between the opposed pubic

articular surfaces.

The superior ramus unites with the ilium and the ischium. The inferior ramus joins the ischial ramus. The body of the pubis bears the pubic crest, a rounded superomedial prominence. The pubic tubercle, on either side of the pubic crest, is an upward directed elevation on the

body, 1-2 cm lateral to the pubic symphysis.

The superior ramus has a pectineal line (pecten pubis).The Obturators


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Foramen, Membrane, and Internus Muscle:

Foramen: An ovoid aperture surrounded by a continuous rim of bone, derived from pubis, ilium,

and ischium.

Membrane: A fibrous sheath that almost completely encloses the obturator foramen leaving asmall superomedial gap through which pass the obturator nerve and vessels.

Internus Muscle:

A lateral rotator of the femur at the hip joint and is supplied by a branch from the sacralplexus (nerve to the obturator internus from L5, S2, & S3).

It arises from the pelvic surface of the obturator membrane and the adjoining part of the hipbone.

The muscle fibers converge to a tendon which leaves the pelvis through the lesser sciaticforamen to be inserted in the greater trochanter of femur.

Upon the perineal surface of the muscle, the obturator fascia (covering the muscle) form atunnel calledpudendal canal (Alcock's fascia). It transmits the pudendal nerve and the

internal pudendal vessels. It connects the lesser sciatic foramen to the posterior edge of theperineal membrane (immediately above the upper edge of the sacrotuberous ligament).


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The Acetabulum

A depression on the outer surface of the hip bone which articulates with the hemisphericalhead of femur.

It is formed by parts of the ilium, the ischium, and the pubis. The Y-shaped line of fusion isoften visible in the floor of the socket.

The raised circumferential perimeter of the acetabulum is interrupted inferiorly forming theacetabular notch. This notch in life is spanned by the transverse acetabular ligament.

The Sacrum


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It is the fusion of the 5 sacral vertebrae. It is a wedge-shaped bone with forward concavity. The upper border (the base): 2 alae, promontory, and the articular surface. It articulates with

L5 via 2 superior articular processes.

The narrow inferior border (apex) articulates with the coccyx. The sacrum is tilted forward so that it forms an angle with L5 calledlumbosacral angle. Laterally, the sacrum articulates with the 2 iliac bones to form the sacroiliac joints. The anterior and upper margins of the 1st sacral vertebrae bulge forward(sacral

promontory).

The anterior and posterior surfaces of the sacrum posses on each side 4 foramina for thepassage of the anterior and posterior rami of the upper four sacral nerves.

The vertebral foramina together form the sacral canal. The lamina of S5, and sometimes those of the 4th, fails to meet in the midline forming the

sacral hiatus.

The sacral canal contains the anterior and posterior roots of the lumbar, sacral, andcoccygeal 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 ofS2.

The pelvic surface:a. Central part formed by bodies of fused sacral vertebrae separated by transverse

ridges.b. 4 pairs of anterior sacral foramina.c. 2 lateral masses.

The dorsal surface:a. Five sacral crests: median, 2 intermediate and 2 lateral.b. 4 pairs of dorsal sacral foramina.c. Inferiorly: 2 sacral cornua. One on each side of the hiatus for the articulation with

the coccygeal cornua.

The Coccyx

It consists of 4 vertebrae fused together to form a small triangular bone. It articulates at its base with the sacrum.


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The coccygeal vertebrae consist of bodies only, but the 1st vertebra possesses a rudimentarytransverse processes and cornua. The cornua project upward to articulate with the sacral

cornua.

Piriformis Muscle

Lateral rotator of the femur at the hip joint. It is supplied by branches from the sacral plexus. It arises from the front of the lateral masses of the sacrum. It passes through the greater sciatic foramen to be inserted into the upper border of the

greater trochanter of the femur.

Ligaments of the pelvis


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1. The sacroiliac ligaments: are extremely strong and pass directly anterior and posterior tothe sacroiliac joint. They bind the sacrum to the pelvis. The strong posterior and

interosseous sacroiliac ligaments suspend the sacrum between the two iliac bones. The

anterior sacroiliac ligament is thin and is anterior to the joint.

2. The iliolumbar ligaments: connect the transverse process of L5 to the iliac crest on eachside. Some inferior fibers of this ligament attach to the lateral margin of the sacrum and arecalled as:

3. Lumbosacral ligament.N.B. The iliolumbar and the Lumbosacral ligaments prevent the rotation of L5 on thesacrum. They also help to prevent the gliding of L5 on the sacrum aided by the presence of

the articular processes between the sacrum and L5.

4. The pubic symphysis: note the superior and inferior pubic (symphyseal=arcuate)ligaments.

5. The sacrotuberous ligament: it is strong and extends from the lateral part of the sacrumand coccyx and the posterior inferior iliac spine to the ischial tuberosity.

6. The sacrospinous ligament: it is triangular in shape. It is attached by its base to the sacrumand coccyx and by its apex to the spine of the ischium.

N.B. The weight of the trunk tends to thrust the upper end of the sacrum downward and rotate

the lower end of the bone upward. This movement is prevented by the sacrotuberous and

sacrospinous ligaments.

N.B. The sacrotuberous and sacrospinous ligaments help to form borders of the greater and

lesser sciatic foramina. The greater sciatic foramen is bounded by these ligaments and the

greater sciatic notch. Similarly, the lesser sciatic foramen is bounded by the lesser sciatic notch

and these 2 ligaments.


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The Pelvis

The pelvis is divided into two compartments by the pelvic inlet (pelvic brim), which isformed by:

a. Posteriorly: The sacral promontory.b. Laterally: The iliopectineal line (arcuate line).c. Anteriorly: The symphysis pubis.

Above the brim is the false pelvis. Below the brim is the true pelvis.False pelvis

Boundaries:

Anteriorly: the lower part of the anterior abdominal wall. Laterally: The iliac fossa and iliacus muscle. Posteriorly: The lumbar vertebrae.

The false pelvis flares out superiorly and is considered part of the abdominal cavity.

True pelvis

It has:

1. Inlet (pelvic brim): forms ~ 55o angle with the horizontal plane.2. Outlet: is bounded by:


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a. Anteriorly: the pubic arch.b. Laterally: the ischial tuberosities.c. Posteriorly: the coccyx.

The pelvic outlet does not present a smooth outline but has 3 notches; the pubic arch and thesciatic notches.

N.B. From an obstetric point of view the sacrotuberous ligaments are 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 in front, and the sacrotuberous ligaments and the

coccyx behind.

3. Cavity: short, curved canal between the inlet and the outlet. It has a shallow anterior walland a much deeper posterior wall.

Pelvic Measurements in Obstetrics

The pelvic axes:

Anatomic axis:

o It is an imaginary line joining the central points of the antero-posterior (AP)diameters from the inlet to the outlet.

o It is C-shaped with the concavity directed forward.

Obstetric axis:

o It is an imaginary line represents the way passed by the head during labour.o It is J-shaped that passes downward and backward along the axis of the inlet till the

ischial spines where it passes downward and forward along the axis of pelvic outlet.


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True Pelvis Measurements

The Pelvic Inlet

Antero-posterior (AP) diameters:

Anatomical AP diameter (true conjugate) = 11 cm.

From the tip of the sacral promontory to the upper border of the symphysispubis.

Transverse diameters:Anatomical = 13 cm.

It is the largest diameter in the pelvis. It is between the outermost two points on the iliopectineal lines.

Oblique diameters (arcuate lines):1. Right oblique = 12 cm.

From the right sacroiliac joint to the left iliopectineal eminence.2. Left oblique = 12 cm.

From the right sacroiliac joint to the left iliopectineal eminence.The Pelvic Outlet


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Antero-posterior (AP) diameters:Anatomical AP diameter = 11 cm (9.5-11.5). Varies because of the mobility of the coccyx.

From the tip of the coccyx to the lower border of the symphysis pubis. Transverse diameters:

1. Bituberous diameter = 11 cm Between the inner aspects of the ischial tuberosities. Usually estimated by the size of a closed fist.

2. Bispinous diameter = 10.5 cm Between the tips of ischial spines.

Sex Differences of the Pelvis


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They 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.

1. The false pelvis is shallow in females and deep in males.2. The inlet is transversely oval in females but heart shape in males (because of the

promontory of sacrum).

3. The cavity in females is cylindrical (i.e. with parallel walls) with the distancebetween the inlet and the outlet is shorter. In males, it is funnel-like with inwardly

slopping walls.

4. The pelvic outlet is larger in females than in males. The distance between theischial tuberosities is longer, the subpubic angle is wider, and the coccyx is more

mobile in females.

5. The ischial tuberosities are everted in females and turned in males.6. The pubic tubercles are more widely separated in females than in males.7. The sacrum is shorter, wider, and flatter in females than in males.8. The greater sciatic notch is wider in females.9. The sub pubic angle (pubic arch is wider in females):

In males: it is between 55o-58o (angle between the index and middle fingers) In females: it is 80o-100o (angle between the thumb and the index finger).

Varieties of the Female Pelvis


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In 1933, Caldwell and Moloy classified female pelves into 4 groups:

I. Gynecoid pelvis: is the typical female pelvis and present in ~ 40-50%.II. Android pelvis: is the male or funnel-shaped pelvis with narrow outlet.

III. Platypelloid pelvis:o The transverse diameters are much greater than the AP diameters (the promontory of

sacrum is pushed forward).

o Sub pubic angle is wide.IV. Anthropoid pelvis:

o All the AP diameters are greater than the transverse diameters. Two other varieties can be added to the above:

V. Contracted pelvis.VI. Asymmetrical pelvis.Pelvic Walls


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Formed by bones and ligaments. Partly lined with muscles covered with fascia and parietal peritoneum. They are: anterior, posterior, lateral, and inferior pelvic walls.

Anterior pelvic wall

Formed by the posterior surfaces of the bodies of the pubic bones, the pubic rami, and thesymphysis pubis.

Posterior pelvic wall

Formed by the sacrum, coccyx, and the piriformis muscles and their coverings of parietalpelvic fascia.

Lateral pelvic walls

Formed by:

a. Hip bone below the pelvic inlet.b. Obturator membrane.c. Sacrospinous and sacrotuberous ligaments.d. Obturator internus muscle and its covering fascia.

Inferior pelvic wall (pelvic floor)

It stretches across the pelvis and divides it into the main pelvic cavity above and theperineum below.


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It is formed by the pelvic diaphragm.Pelvic Diaphragm

o Formed by levator ani muscles, coccygeus muscles, and their covering fascia.o It is incomplete anteriorly for the passage of the urethra (and vagina in females).

Levator Ani Muscle

I. Origin:

II.o The line of origin extends from the pubis to ischial spines and includes a thickened

obturator fascia along the medial surface of the obturator

Internus (the arcus tendineus).

III. Insertion:


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o Muscle fibers converge medially to their insertion. The line of insertion extendsfrom the pubis anteriorly to the coccyx posteriorly.

IV. Perforations:o Anteriorly: urethral and vaginal orifices (the bulb of the penis in males).o Posteriorly: the anal orifice.o In between: the perineal body.

The anal orifice and the coccyx are joined by the thickened anococcygeal raphe.

V. Divisions:Anterior fibers: 3 parts

1. (the levator prostate or sphincter vagina

Arises from the body of the pubis. Forms a sling around the prostate or vagina. Inserts into the perineal body. Support the prostate (vagina) and stabilize the perineal body.


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2. Puborectalis:

Arises from the body of the pubis. Forms a sling around the junction of the rectum and anal canal

(anorectal junction) to end in the body of the pubis of the oppositeside.

This part is best seen from an outside (exterior) view. Many fibers blend with the external anal sphincter (prerectal muscle

fibers of luschka)

3. Pubococcygeus:

1. From the body of the pubis and the tendineus arc.2. Inserts into the anococcygeal body.

Posterior fibers (The iliococcygeus):


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Arises from the arcus tendineus and the ischial spine. Inserts in the coccyx and the anococcygeal body.

V. Actions of levator ani muscles:A. Support and maintain pelvic viscera in position.B. Resist the rise in the intrapelvic pressure during straining.C. Sphincter action on the anorectal junction (vagina).

VI. Nerve Supply:

. Perineal branch of S4.A. Perineal branch of the pudendal nerve.

Coccygeus Muscle

Small triangular muscle that makes up the lower part of the posterior pelvic wall just belowthe piriformis.

It arises from the ischial spine. Inserts into the lower end of the sacrum (S5) and into the coccyx.


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It is the muscle that sways the tail in dogs (wagging the tail). Nerve supply: a branch of the S4 and S5.

N.B. The piriformis muscle appears to "fill in" the gap between the posterior edge of the coccygeus

and the sacrum, but it is not a true pelvic floor muscle.

Pelvic Fascia

Formed of connective tissue. Continuous above with the fascia lining the abdominal wall (fascia transversalis). Continuous below with the fascia of the perineum. It is divided into parietal and visceral layers:

Parietal layer

Lines the walls. It is named according to the muscle it overlies, e.g. obturator internus fascia.

The coccygeus and levator ani fascia is the superficial layer of the pelvic fascia.

As the diaphragm becomes deficient anteriorly, it becomes continuous with (or as) thesuperior fascia covering the superior surface of the pelvic diaphragm (i.e. in the perineum).

N.B. In many locations, where the parietal fascia comes into contact the bone it fuses withthe periosteum.

Below, in the perineum, it forms the superficial layer of the urogenital diaphragm.Visceral layer

It is a layer of loose connective tissue.


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It covers and supports all the pelvic viscera. In certain locations, the fascia thickens to form fascial ligaments (e.g. ligaments of the

parametrium).

Pelvic peritoneum

The parietal peritoneum lines the pelvic walls. It reflects onto the pelvic viscera where it becomes continuous with the visceral peritoneum It forms the pouch of Douglas and the vesicouterine pouches.

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Bony pelvis, pelvic walls, and pelvic measurements text_P.pdf