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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.