Pelvis, Perineum, and Pregnancy Quiz

• The study notes cover the bony pelvis, pelvic wall, and floor, essential for understanding the anatomy of the abdomen and pelvis.

Introduction

• The pelvis is the inferoposterior part of the trunk, connecting the abdomen and lower extremities.
• Pelvic cavity: bowl-shaped space within the bony pelvis and perineum that contains urinary organs, genitals, rectum, and anal canal.
• The perineum is a diamond-shaped area inferior to the pelvic floor, containing the anus and external genitalia.

Bony Pelvis

• The pelvic girdle transfers weight, provides muscle attachment, supports abdominopelvic structures and viscera, and provides attachment for external genitalia.

Bones

• Composed of two hip bones, the sacrum, and the coccyx.
• Hip bones consist of the ilium, ischium, and pubis, which are united by the triradiate cartilage during infancy and childhood.
• The triradiate cartilage fuses during puberty to form the acetabulum, which articulates with the femur.
• Separate bones indicate an individual is younger than 12 years old.

Hip Bones: Ilium

• The ilium is the superior fan-shaped portion, attaching the buttocks muscles.
• Gluteus maximus attaches to the posterior gluteal line.
• Gluteus medius attaches to the anterior gluteal line.
• Gluteus minimus attaches to the inferior gluteal line.
• The iliac crest is the superior edge of the iliac wing, ending at the anterior and posterior superior iliac spines.
• The intercristal line, connecting the superior aspect of iliac crests, is located at L4 on spinal imaging and is used as a landmark for lumbar taps and epidurals.
• The arcuate line is on the internal surface, joining the pectineal line of the pubis to demarcate the pelvic inlet.

Hip Bones: Ischium

• The ischium is an L-shaped bone forming the posteroinferior part, serving as attachment for the gemellus muscles.
• The body of the ischium contributes to the formation of the acetabulum.
• The ischial ramus contributes to the obturator foramen, fuses with the inferior pubic ramus, and ends as the ischial tuberosity.
• The ischial tuberosity is a large posteroinferior protuberance that bears body weight when seated; it is also known as the "sit-down bone."
• With the body seated, the gluteus maximus shifts superiorly, exposing the ischial tuberosity to the surface.
• Ischial spine: small posteromedial projection at the junction of the body and ramus of the ischium that divides the innominate bone into the greater and lesser sciatic notches.

Hip Bones: Pubis

• Pubis: anteroinferior portion of the pelvic girdle
• Superior Ramus: forms the acetabulum and contributes to the obturator foramen.
• Inferior Ramus: forms the obturator foramen together with the ischial ramus.
• Pubic Crest: thickening of the anterior part of the pubic body.
• Pubic Tubercle: swelling at the lateral end of the pubic crest where the inguinal ligament attaches.
• Pecten Pubis/Pectineal Line: thickened oblique ridge on the superior ramus that connects with the arcuate line to form the pelvic inlet.
• Pubic Arch: formed by the ischiopubic rami of both sides.
• Ischiopubic Rami: conjoined inferior ramus of the ischium and inferior ramus of the pubis.
• Subpubic Angle: inferior border of the pubic arch, with width determined by the distance between the ischial tuberosities.

Sacrum

• Sacrum: triangular bone formed by the fusion of five sacral vertebrae, providing strength and stability.
• Contains the cauda equina, spinal nerve roots arising inferior to L1.
• Sacral Promontory: anteriorly projecting edge of S1, serving as a landmark.
• Auricular Process: forms the lumbosacral joint.
• Pelvic Surface: smooth & concave.
• Dorsal Surface: irregular, rough, and convex.
• Median Sacral Crest: fused spinous processes.
• Intermediate Sacral Crests: (2) fused articular processes.
• Lateral Sacral Crests: (2) fused transverse processes.
• Sacral Hiatus: opening due to the absence of laminae & spinous processes of S4-S5.
• The sacral hiatus contains connective tissue, the filum terminale, S5 nerve, and coccygeal nerves, and is palpable at the inferior sacrum.
• Sacral Cornua: inferior articular process of S5.

Coccyx

• Coccyx: tailbone, fusion of 3-5 rudimentary coccygeal vertebrae.
• All coccygeal segments lack pedicles, laminae, and spinous process.
• It represents the remnant of the tail of the human embryo.
• Bony Landmarks:
• Intercristal Line (L4 or L4-L5): line between iliac crests posteriorly used for lumbar tap, spinal anesthesia.
• S2 spinous process (between PSIS)
• Skin dimples: skin and deep fascia mark these landmarks.

B. Ligaments

• Sacroiliac Ligaments: connect the sacrum to the ilium, reinforcing the sacroiliac joint
• Anterior Sacroiliac Ligament: stabilizes the joint and resists excessive anterior movement.
• Posterior Sacroiliac Ligament: helps maintain pelvic stability by preventing excessive movement of the sacrum.
• Iliolumbar
• Extends from the iliac crest to the transverse processes of L4-L5.
• Stabilizes the junction between the lumbar line and cecum.
• Sacrotuberous: posterior ligament to support the sacroiliac joint
• Extends from sacrum to ischial tuberosity and helping to form the lesser sciatic foramen
• Sacrospinous: posterior ligament to support the sacroiliac joint
• Extends from sacrum to ischial spine
• Converts the greater sciatic notch into the greater sciatic foramen

Lesser Sciatic Foramen

• Lesser Sciatic Foramen: passageway between sacrospinous and sacrotuberous ligaments.
• The lesser sciatic foramen serves as an entrance for vessels from the gluteal region to the perineum and transmits pudendal vessels.
• Obturator canal: small space in the fascia covering obturator foramen through the ischium and pubis.
• The obturator canal passageway transmits the obturator vein, artery, and nerve from the pelvis to the thigh.
• Greater and lesser sciatic foramina are important doorways for structures entering or exiting the pelvis.

C. Foramina: Greater Sciatic Foramen

• Provides a major exit from the true pelvis and a route of communication between the pelvic cavity and lower limbs.
• Sciatic and pudendal nerves and gluteal nerves and vessels pass through this foramen.

D. Orientation

• The pelvis is tilted forward when standing upright
• Anterior superior iliac spine (ASIS) and pubic tubercles lie on same vertical plane
• Roof: sacral promontory, positioned superior to the center of the pelvic outlet.
• Floor: ischiopubic rami (pubic bones)

E. Pelvic Planes

• Superior Pelvic Aperture (Pelvic Inlet), Inferior Pelvic Aperture (Pelvic Outlet), Pelvic Midplane
• Superior Pelvic Aperture: regularly measured during a pelvic examination which can obstruct the delivery of the baby since it passes through during vaginal delivery
• Three pelvic planes: Superior Pelvic Aperture (Pelvic Inlet)

False Pelvis (Greater Pelvis or Pelvis Major)

• Contains the inferior abdominal viscera, larger in size and superior to the pelvic brim
• Boundaries include anterior abdominal wall, iliac fossae, L5 and S1

True Pelvis (Lesser Pelvis or Pelvis Minor)

• Contains the pelvic viscera and inferior to the pelvic brim, smaller in size and enclosed inferiorly by pelvic diaphragm

A. Superior Pelvic Aperture or Pelvic Inlet

• Boundary between greater and lesser pelvis at the pelvic brim
• Has anteroposterior (obstetric conjugate is more significant) and transverse diameters that influence shape

Pelvic Measurements of the Inlet

• Anteroposterior (AP) Diameter: obstetrically significant.
• Obstetric Conjugate: AP distance that is clinically important during childbirth distance between middle of pubic symphysis and sacral promontory.
• Transverse Diameter: Distance between right and left arcuate lines.
• Oblique Diameter: Distance between one sacroiliac joint and contralateral iliopubic eminence.

B. Inferior Aperture or Pelvic Outlet

• Found at the level of the ischial tuberosities, with two diameters: Anteroposterior and Transverse.

C. Pelvic Midplane

• It is found at level of the ischial spines and the narrowest diameter in the pelvis.
• Palpate the left and right ischial spine to assess the position of the baby
• If the head of the baby already passed the ischial spines, then they have already passed the midplane

D. Sexual Dimorphism

• The table outlines key differences between male and female pelvis
• Female: thin and light bones, shallow greater pelvis and cylindrical lesser pelvis, oval-shaped and wide pelvic inlet, large pelvic outlet, wide pubic arch, oval obturator foramen, and almost 90-degree greater sciatic notch.

IV. Pelvic Joints

• The bony pelvis has two sacroiliac joints, lumbosacral/sacrococcygeal joints, and pubic symphysis.
• Pubic ligaments would relax and the interpubic disc would increase in size to allow for childbirth.
• The obstetric conjugate remains unaffected.

A. Sacroiliac Joints

• Paired synovial joints between auricular surfaces of the sacrum and ilium and covered by Sacro-iliac Ligaments

B. Lumbosacral Joints

• Joint complex composed of three articulations: anterior intervertebral (IV) between the bodies of L5 and S1 and strengthened by the iliolumbar ligament

C. Pubic Symphysis

• The pubic symphysis is located between the bodies of the (2) pubic bones and a fibrocartilaginous interpubic disc
• Thickened superiorly, has (2) parts
• The 10% increase occurs in pelvic diameters except for the obstetric conjugate.

V. Pelvic Wall

• Pelvic Cavity is formed by the pelvic bones, superficial and deep muscles, blood, lymphatic vessels, ligaments and nerves
• Antero-inferior wall: Bodies & Rami of Pubic Bones
• Lateral walls: Obturator membrane and obturator internus Posterior wall: Sacrum and Coccyx

A. Antero-inferior Pelvic Wall

Formed by the bodies and rami of the pubis.

B. Lateral Pelvic Wall

Composed of hip bones, obturator internus muscle Obturator internus: covered by obturator membrane, turns laterally attaching to greater trochanter through lesser sciatic foramen and rotates the thigh laterally

C. Posterosuperior Pelvic Wall

• Formed both wall and roof of the pelvis and composed of the following: Sacrum, adjacent parts of ilium, and coccygeus muscle and coccyx, Anterior sacroiliac ligament Piriformis: lines the posterior wall of the pelvis.

VI. Pelvic Floor

• Diaphragm is funnel-shaped, formed by piriformis and obturator internus
• Important muscles include the levator ani muscle

A. Pelvic Diaphragm

• Consists of the levator ani muscle, coccygeus muscle, perineal membrane, and deep perineal pouch

Levator Ani

• Located at Ischial spines, tendinous arch and body of pubic bones

Muscles of the pelvic diaphragm and its parts

• Important to support the viscera and for blood supply, its venous drainage to internal Iliac vein allows the anastomosis of venous drainage to the brain and can be lead to metastasis

Pelvic Prolapse as Clinical Correlate

• Pelvic Organ Prolapse
• Portion of pelvis comes out due to laxity support of (4) parts
• Anterior portion of vagina (Cystocele), Posterior portion of where the intestine or rectum come out in rectocele), Other organs (e.g., uterus) also comes out in worse cases

VII. Nerves of the Pelvis and Perineum

• Innervated mainly by:
• Sacral plexus (L4-S4) or
• Coccygeal Plexus (formed from ventral rami of S4, S5, and coccygeal nerves to supply coccygeal muscle), Piriformis Muscle and deep to the inguinal ligament

A. Lumbar Plexus

• Forms the lateral wall of the pelvis

Clinical correlate on the Obturator Nerve

• Obturator Nerve, The obturator nerve can be injured during difficult pelvic surgery such as harvesting lymph nodes in ovarian cancer patients. *Know the outcomes of injures to the Obturator

B. Lumbosacral Trunk

Joins Sacral Plexus, and forms on the posterior wall from anterior rami of L4-5

C. Sacral Plexus

Forms on posterior wall from anterior rami of L4-S4

Superior and Inferior Gluteal Nerve

• Supply the buttock and run through this plane

Sciatic Nerve

Arises from L4 to S3, Is main nerve to lower limb

Pudendal Nerve

• Arises from S2-S4 along with the internal pudendal artery goes to hook around the Sacrospinous ligament for the main innervation to perineum chief sensory nerve to external genitalia

Pudendal Nerve Block

Provides an approach to Pudendal Nerve is concerned with the area between S2-S4 and lower quarter of the vagina

D. Other Nerves.

Summarized the NERVE and FUNCTION of the:

• Obturator nerve
• Pudendal nerve
• Inferior rectal nerve
• Perineal nerve
• Dorsal penile
• Clitoral nerve and the function on what nerves in pelvis and its action

VIII. Peritoneum

Does not reach pelvic it creates a series of fold and recess that covers the pelvic viscera bladder and the create or pouch

IX. Pelvic Fascia

Connective tissue in that area around the pelvis to provide structure and stability for: Parietal Pelvic Fascia and Visceral Pelvic Fascia

X. Internal Iliac Artery

• Begins at the Level of L5 when this divides, what it supplies, where it runs

Branches of the Division

• Anterior or Posterior Division: what does each entail and supply
• Obturator and Superior Vesical Artery: comes from umbilical with the other vessels from this Artery

Uterine and Vaginal Arteries

XI. Postpartum Hemorrhage

The amount of loss in both scenarios (Vaginal and in Cesarean section/ what is used to determine Main causes (4T's): What does each entail, how does the body react and how to solve it/ What happens is placenta is adhered and difficult to expel

Managment

Important to do (5) main steps and is broken down on how to follow and understand: Bilateral ligation

Steps if Uterus is Not Responding.

• The body has a special Collateral Circulation: Anastomoses are important for collateral circulation to the uterus if the internal iliac artery is ligated

XII. Ureter

The Ureter goes through (3) different layers of the urinary system: Anterior to Bifurcation of Common iliac,

Points of injury or Damage

• What is to point out for safety measure: ( mnemonic: Water that is Under the Bridge)

The (4) Areas/Points Of Injury

• remember where the structures lie compared to each other

XIII. Internal Iliac Vein.

The Drainage Sites are important to identify: Superior Rectal Vein, Superior Gluteal Vein, Lateral Sacral Veins.

Clinical Correlates

Understanding of important anatomical relationships in the context of clinical scenarios, such as injury to the obturator nerve during lymph node harvesting or lymphatic drainage patterns in cancer metastasis

XIV. Lymphatic Drainage

Lymph from the pelvis and the perineum will travel through different groups of lymph nodes Ultimately drains into the thoracic duct Usually follows venous pathways except for structures that drain to the external iliac nodes Infections can be caused by injury or any other means Clinically, a common condition in the Lymphatic Drains is the Painful lesions/wounds in the vulva

• for Cancers, check for lymph node involvement in vulvar and cervical cancers
• Oncologists identify the most likely nodes to be positive (Malignancy During Surgery)

Test your knowledge of the pelvis, pelvic cavity, and perineum. Questions cover the functions of the pelvic girdle, impact of muscle damage, and anatomical landmarks. Also includes questions on postpartum hemorrhage.