dr. sreekanth thota department of anatomy pelvis and perineum

WINDSOR UNIVERSITYSCHOOL OF MEDICINE

Dr. SREEKANTH THOTA

DEPARTMENT OF ANATOMY

Pelvis and Perineum

Pelvis

Introduction Bones and Features of the Pelvic Girdle Pelvic wall Pelvic nerves Pelvic arteries Pelvic veins Pelvic lymph nodes

Pelvis

Pelvis is the part of the trunk infero posterior to the abdomen and is the area of transition between the trunk and the lower limbs.

Perineum The perineum is inferior to the floor

of the pelvic cavity; its boundaries form the pelvic outlet. The perineum contains the external genitalia and external openings of the genitourinary and gastrointestinal systems

Subdivision of Pelvis

The pelvis is divided into two regions The superior region is the false pelvis

(greater pelvis) and is generally considered part of the abdomen .

The true pelvis (lesser pelvis) is related to the inferior parts of the pelvic bones, sacrum, and coccyx, and has an inlet and an outlet.

Greater pelvis and lesser pelvis

Greater pelvis

Above the pelvic brim

Forms the lowest part of the abdominal cavity

Lesser pelvis Below the

pelvic brim Above is

opened into the abdominal cavity

Below is closed by the pelvic diaphragm

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Bones and Features of the Pelvic Girdle

In the mature individual, the pelvic girdle is formed by three bones

Right and left hip bones:develops from the fusion of three bones, the ilium, ischium, and pubis.

Sacrum: formed by the fusion of five, originally separate, sacral vertebrae.

Component Parts

Pelvic inlet Pelvic outlet

Pelvic inlet

The pelvic inlet is somewhat heart shaped and completely ringed by bone .

Posteriorly, the inlet is bordered by the body of vertebra S1, which projects into the inlet as the sacral promontory

Laterally, a prominent rim on the pelvic bone continues the boundary of the inlet forward to the pubic symphysis, where the two pelvic bones are joined in the midline.

Pelvic outlet

The diamond-shaped pelvic outlet is formed by both bone and ligaments.

Two ligaments-the sacrospinous and the sacrotuberous ligaments-are important architectural elements of the walls because they link each pelvic bone to the sacrum and coccyx . These ligaments also convert two notches on the pelvic bones-the greater and lesser sciatic notches-into foramina on the lateral pelvic walls

Comparison of Male and Female Bony Pelvis

Bony Pelvis Male Female

General structure Thick and heavy Thin and light

Pelvic inlet Heart shaped, narrow Oval and rounded; wide

Pelvic outlet Comparatively small Comparatively large

Pubic arch Narrow (< 70°) Wide (> 80°)

Acetabulum Large Small

Diameters of Pelvic Inlet

Assessing the diameters of Pelvis is important to predict success of vaginal delivery of fetus thru’ birth canal.

Pelvic Diameters (Conjugates)

Diagonal conjugate: The distance from the promontory of the sacrum 

to the lower margin of the pubic symphysis. Also called false conjugate.

True conjugate:  radiographic measurement of the distance from the upper margin of the symphysis pubis to the sacral promontory. It is usually 1.5 to 2 cm less than the diagonal conjugate. 

Procedure used in measuring the diagonal conjugate

Different types of pelvic inlets

The gynecoid type, present in about 41% of women, is the typical female pelvis.

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.

Pelvic wall

Structure of the Pelvic Walls 1.Anterior Pelvic Wall 2. Posterior Pelvic Wall 3. Lateral Pelvic Wall 4. Inferior Pelvic Wall, or Pelvic Floor

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.

It participates in bearing the weight of the urinary bladder.

Anterior wall of the pelvis (posterior view).

Posterior Pelvic Wall

The posterior pelvic wall is extensive and is formed by the sacrum and coccyx and by the piriformis muscles.

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

Inferior Pelvic Wall, or Pelvic Floor

Pelvic Diaphragm

The pelvic floor is formed by the bowl- or funnel-shaped pelvic diaphragm, which consists of the coccygeus and levator ani muscles and the fascias.

The floor of the pelvis supports the pelvic viscera and is formed by the pelvic diaphragm.

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

Pelvic Diaphragm

1. Levator Ani Muscle A.Anterior fibers: 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.

B.Intermediate fibers: Puborectalis forms a sling around the junction of

the rectum and anal canal Pubococcygeus passes posteriorly to be

inserted into a small fibrous mass, called the anococcygeal body

Puborectalis muscle

The puborectalis forms a puborectal sling, the tonus of which is responsible for maintaining the anorectal angle (perineal flexure).

Puborectalis portion is important in maintaining fecal continence immediately after rectal filling or during peristalsis when the rectum is full and the involuntary sphincter muscle is inhibited (relaxed).

Pelvic Diaphragm

C. Posterior fibers: The iliococcygeus is inserted into the anococcygeal body and the coccyx.

2. Coccygeus Muscle(ischio-coccygeus):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

Nerve supply: Fourth and fifth sacral nerve (pudendal nerve)

Main Action of Pelvic Diaphragm The levatores ani muscles of the two

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

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

The levator ani must relax to allow urination and defecation

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).

Arteries and Veins of Pelvis

Arteries of the Pelvis

Common Iliac Artery External Iliac Artery 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 originates from the common iliac artery on each side, approximately at the level of the intervertebral disc between LV and SI and lies anteromedial to the sacro-iliac joint.

Branches of the anterior trunk

1.Umbilical artery: superior vesical artery

2.Inferior vesical artery 3.Middle rectal artery 4.Uterine artery 5.Vaginal artery 6.Obturator artery 7. Internal pudendal artery 8.Inferior gluteal artery

Uterine and vaginal arteries

Posterior trunk

Branches of the posterior trunk of the internal iliac artery are the

1.Iliolumbar artery 2. Lateral sacral artery 3.Superior gluteal artery

Veins

Pelvic veins follow the course of all branches of the internal iliac artery except for the umbilical artery and the iliolumbar artery.

On each side, the veins drain into internal iliac veins, which leave the pelvic cavity to join common iliac veins situated just superior and lateral to the pelvic inlet

Nerves of Pelvis and Perineum

Sacral Plexus

The sacral plexus lies on the posterior pelvic wall in front of the piriformis muscle .

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 . The fourth lumbar nerve joins the fifth lumbar nerve to form the lumbosacral trunk.

Branches to the pelvic muscles, pelvic viscera, and perineum:

The pudendal nerve (S2, 3, and 4) It passes between the  piriformis and 

coccygeus muscles and leaves the pelvis through the lower part of the greater sciatic foramen.

It crosses the spine of the ischium, and reenters the pelvis through the lesser sciatic foramen.

Pudendal nerve (Imp)

Pudendal canal

The pudendal canal (also called Alcock's canal) is an anatomical structure in the pelvis through which the internal pudendal artery, internal pudendal veins, and the pudendal nerve pass.

Pudendal nerve block

The anesthesia is produced by blocking the pudendal nerves near the ischial spine of the pelvis.

A pudendal block is usually given in the second stage of labor just before delivery of the baby.

It relieves pain around the vagina and rectum as the baby comes down the birth canal.

It is also helpful just before an episiotomy .

Pudendal nerve block

Autonomic Nerves

Pelvic Part of the Sympathetic Trunk Pelvic Splanchnic Nerves Superior Hypogastric Plexus Inferior Hypogastric Plexuses

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.