Clinical Anatomy of the Female

PelvisFor the

ObstetricianProfessor Hassan Nasrat

The Bony Pelvis

The ileopectineal line divides the pelvis into the false and the true pelvis

The normal female pelvis is described as “gynecoid” to be differentiated from the male “android pelvis”.

The pelvic inlet “pelvic brim”

Engagement of the fetal head usually occurs through the transverse diameter

13 cm

Ante

ro-

post

eri

or

Transverse

12

cm

The pelvic cavity:

Is the curved canal between inlet and outlet. In the normal female pelvis the cavity is circular in shape and curves forwards. All its diameters measureapproximately 12 cm.

The Pelvic Cavity

The Pelvic Outlet

the two pubic bones make the pubic arch, which in the normal female pelvis forms anangle not less than 90°. A narrow angle will force the fetal head at delivery posteriorly andthus increase the risk of perineal tear

Pelvic ligaments and Diaphragm

The pudendal neurovascular bundle exits out of the greater sciatic foramen and reenters the pelvis through the lesser sciatic foramen. This is the site for administration of pudenal block for local anesthesia.

A triangular muscle arises from the ischial spine and inserts onto the sacrum and coccyx

The two main muscles: The levator ani muscle group:

The coccygeus muscles

Pubococcygeus, puborectalis, and iliococcygeus. They muscles extend from the lateral pelvic walls downward and medially to fuse with each other posteriorly.The levator hiatus lies anteriorly and accommodates the urethra, vagina, and anus.

The Perineum

The perineum is divided into two parts (or triangles):Anterior or urogenital triangle:

Posterior or anal triangle:

The midline attachment forms the fibromuscular perineal body. between the anal canal and the vagina

Subdivided into:A superficial and deep perineal spaces by a fibromuscular septum called the urogenital diaphragm

The Perineum

The Superficial Perineal Space

Boundaries of the Superficial

Perineal Space

Note that the superfial muscles of the urogenital triangle and the muscles of the anal triangle all converge in the midline at the central tendon of perineum (perineal body) .

Is bounded by three sets of muscles:•The ischiocavernosus:•The bulbocavernosus (the sphincter of the Vagina):•The superficial transverse perinei: It also includes the Bartholin’s glands and the vestibular bulbs.

The superfial muscles of the urogenital triangle and the muscles of the anal triangle all converge in the midline.

During episiotomy: It is important to recognize superficial transverse perineil-muscle in order to ensure proper cooptation.

The Deep Perineal Space

The Anal Triangle

The anal triangle is the area of the perineum behind an imaginary line that extends between the ischial tuberosities.

The ischiorectal fossae : •A potential space that allows distention of the rectum during defecation and the vaginal wall during second stage of labor.

•It is also a potential space for huge (up to one liter) hematoma collection and abscess formation.

•The obturator nerve and internal pudendal vessels: run alongside the lateral wall of the ischiorectal fossa in the pudendal or Alcock’s canal. This canal is formed from the splitting of the fascia on the lateral wall of the ischiorectal fossa together with the obturator fascia itself.

The external anal sphincter: The voluntary muscle which is responsible for fecal continence is located within the anal triangle. Its total length is about 2 cm, and it is composed

Tear of external anal sphincter is not uncommon during delivery particularly operative one and should be carefully repaired. Failure to recognize tears of the external sphincter or inappropriate repair can precipitate anal incontinence.

The Pudendal nerve (S2-4)

Ilioinguinal nerve (L1) and

genitofemoral nerve (L1, 2)

Perineal branch of posterior femoral cutaneous nerve

Coccygeal and last sacral nerves (S4, 5)

Nerve Supply of the Perineum

The Uterus

In 75% the uterus is in the anteverted, anteflexed position. On rare occasion a retro-verted gravid uterus may get entrapped within the pelvis and beneath the sacral promontory, giving rise to anterior sacculatoin of the uterus. Clinically this presents with acute retention of urine.

The

Uterin

e B

ody

The Isthmus is the short constricted area that marks the junction of the uterine body with the cervix.

Cerv

ix

Isth

mus

It has three layers: The endometrium, the myometrium and the perimetrium:

The myometrium: Has longitudinal, circular and oblique muscle fibers and is very expansile. The oblique muscle fibers run “criss-cross” and compress the blood vessels when the uterus is well contracted. It is found mostly in the upper segment of the uterus, where the placenta normally embeds. The richness in muscle fibers and its criss-cross important to ensure proper hemostasis following placental delivery. In contrast to that is the lower uterine segment which is poor hemostasis following placental delivery. This explains why bleeding in the third stage is more difficult to control if the placenta is implanted in the lower uterine segment as in cases of placenta praevia.

The Endometrium: During pregnancy and childbirth, the endometrium is referred to as the decidua.

The perimetrium: Is a layer of peritoneum that covers the uterus except at the sides where It extends to form the broad ligaments. Significant bleeding and hematoma can extend whithin the layers of the broad ligament into the extra peritoneal space with serious consequences

The body of the uterus:

Consists predominantly of collagenous connective tissue and mucopolysaccaride ground substance.

It communicates with the uterine cavity through the internal os and with the vaginal canal through the external os.

The endocervical canal is about 2.5 to 3 cm in length. It is lined by a single layer of specialized columnar epithelium and secretes mucus to facilitate sperm transport.

During pregnancy the glands secretion forms a plug of mucus which helps protect against infection.

This plug of mucous comes away stained with some blood just before labor commences. Many women refer to this as the “show”.

The Cervix:

Vascular Supply of the pelvis

Note the Ureter Crosses below the Uterine Artery about 1 cm from the cervix

Note the anastomsis between the ovarian and uterine artery.Therefore the uterus receive blood supply from two sources on each side

Vessels and nerves of the deep perineal space

Innervations of the Pelvis Routes of Nerve Supply

to the uterus (visceral nerves). Pain of uterine contractions in the first stages is felt in the abdomen, lower back

Routes of Nerve Supply to cervix and upper vagina (Somatic nerves)In the second stage additional source of pain from cervical stretching and perineal pressure.