Normal Pelvic Anatomy Flashcards
Outline the normal pelvic anatomy
It is formed by 4 bones: 2 hip bones(ischium, ileum, pubis), 1 sacrum, 1 coccyx
These are united together by 4 joints:
- 2 sacroiliac joints
- sacrococcygeal joint
- pubic symphysis
Diameters (conjugates) of the female pelvis
Anatomical conjugate: from pubic symphysis to sacral promontory
Transverse diameter: greatest width of the pelvic inlet
Oblique diameter: from the iliopectineal eminence of one side to the opposite sacro- iliac joint
Straight conjugate: from lower border of symphysis to coccyx
Outline the borders of the pelvic inlet and outlet
Outline the dimensions of the pelvic inlet and outlet
- Inlet is wider but shorter (hodros)
- Outlet is narrower but longer (lignos)
Rotation of baby’s head and shoulders due to the dimensions of pelvic inlet and outlet
Notice posterior part of baby’s head is bigger - this should be coming out anteriorly
Outline the clinical significance of the ischial spine
- Landmark for pudendal nerve block
- Important to assess the progress of labour → acts as a reference point for whether the head of the baby is coming down or not
- If at level of ischial spine: station 0
- 1cm above: -1
- 2cm above: -2 etc
- 1cm below ischial spine: +1 etc
Outline the clinical significance of the sacral promontory
- Sacral promontory
- Used to fix prolapse
- If uterus is slipping down via vagina and woman wants to maintain uterus → it can be pulled up and screwed to promontory
- Can also do mesh procedures, but this is controversial now
Outline the clinical significance of the iliopectineal ligament
Reflected part of inguinal ligament
If someone has stress incontinence, surgery is done in which vagina is pulled and stitched either side
Which pelvic structures are palpable during physical examination?
Outline the differences between the female and male pelvis
- General: Female pelvis somewhat lighter in weight and wider laterally but shorter superiorly to inferiorly, and less funnel-shaped; less obvious muscle attachment points in female than in male
- Sacrum: Broader in female, with inferior portion directed more posteriorly; the sacral promontory projects less anteriorly in female
- Pelvic inlet: Heart-shaped in male, oval in female
- Pelvic outlet: Broader and more shallow in females
- Subpubic angle: Less than 90 degrees in males; 90 degrees or more in females
- Ilium: More shallow and flared laterally in female
- Ischial spines: Farther apart in female
- Ischial tuberosities: Turned laterally in female and medially in male
- Acetabulum: Large and faces laterally in males, small and faces anteriorly
Outline the joints of the pelvis
Sacroiliac (x2)
- Synovial joints between the auricular surfaces of the sacrum and ileum on each side
- Articulate surfaces of the sacro-iileac joints are ROUGH and are said to be auricular in shape – they cannot slide.
- Ligaments also hold them closer. NO MUSCLES act on this joint. Only ligaments stabilise it.
- Ligaments that connect this joint are the anterior ileo-sacral ligaments and the posterior Ileo-sacral ligaments
Pubic Symphysis
- Fibrocartilagenous disc - shock absorber (it can compress) (the articulating surfaces have myeline cartilage and the bones are joined by a layer called disc)
- There is a hormone called relaxin that allows more water to enter the ligaments and allows it to relax. The joints of the child do not detach but they slide over each other.
The sacrococcygeal joint
- Secondary cartilaginous joint which consists of an intervertebral disc between sacrum and coccyx accessory ligaments
- Located between sacrum and coccyx-at the end of labour allows the coccyx to be deflected backwards facilitating delivery of the foetus
Lumbosacral Joint
- Between sacrum and last lumbar vertebra (L5)
Outline the ligaments of the female reproductive tract
Series of structures that support the internal female genitalia in the pelvis → act to support the female viscera and provide a conduit for neurovascular structures
Can be divided into three categories
- Broad ligament: sheet of peritoneum, associated with uterus and ovaries
- Uterine ligaments
- Ovarian ligaments
Broad ligament
- Flat sheet of peritoneum associated with the uterus, fallopian tubes and ovaries
- Extends from the lateral pelvic walls on both sides and folds over the internal female genitalia, covering their surface anteriorly and posteriorly
- Can be divided into three regions, anatomically
- Mesometrium: surrounds the uterus; runs laterally to cover the external iliac vessels; also encloses proximal part of round ligament of uterus
- Mesovarium: part of broad ligament associated with ovaries; projects from posterior surface of broad ligament and attaches to the hilum of the ovary but does not cover the surface of the ovary itself
- Mesosalpinx: originates superiorly to mesovarium, enclosing fallopian tubes
There are three other key ligaments located within the broad ligament:
- Ovarian ligament
- Round ligament of uterus
- Suspensory ligament of ovary (aka infundibulopelvic ligament)
Ligaments associated with the uterus
- Superior aspect of uterus: supported by the broad ligament and round ligaments
- Middle aspect: supported by the cardinal, pubocervical and uterosacral ligaments
- Angle of inlet of the pelvis is not horizontal i.e. the line from sacral promontory to pubic symphysis – the angle is inclined and known as angle of inclination → hence when you palpate, you can still feel the pelvic organs
- As a result of this angle, uterosacral ligament acts as most important support for these organs – supports them posteriorly. Due to gravity, the uterus is falling anterio-inferiorly and this ligament acts to hold it in position
- Inferior aspect: supported by structures in the pelvic floor (levator ani, perineal membrane, perineal body)
Round ligament
- Remnant of the embryonic gubernaculum
- Originates at the uterine horns and attaches to the labia majora, passing
- through the inguinal canal
- Can be a source of pain during pregnancy due to the increased pressure
- placed on it by the expanding uterus
Cardinal ligaments
- Aka lateral, transverse cervical, or Mackenrodt’s ligaments
- Situated along the inferior border of the broad ligament, housing the uterine
- artery and uterine veins
- When a hysterectomy is being performed due to a malignancy, the cardinal ligaments are often removed as they are common reservoir of cancerous cells
Pubocervical ligaments
- Bilateral structures attaching the cervix to the posterior surface of the pubic symphysis
Uterosacralligaments
Bilateral fibrous bands attaching the cervix to the sacrum
Outline the neuromuscular characteristics of the pelvis
- The walls of the organs in the pelvis have SMOOTH MUSCLE and the innervation is PARASYMPATHETIC.
- Pain felt here is poorly localised – due to its referred location. Referred pain occurs because the sensory nerves transmit signals up the same tracts of the dermatomes.
- Sympathetic afferents enter the spinal cord to transmit pain – wherever it enters at a particular level, the pain comes from that equivalent dermatome. Most pain is felt in the MIDLINE – because the autonomic ganglia (SPLANCHIC NERVE GANGLiA) are near the vessels of the midline.
- Main muscles of the pelvic diaphragm are the levator ani (puborectalis, pubococcygeus, iliococcygeous) and coccygeus
POP-Q (pelvic organ prolapse) questionnaire to quantify degree of prolapse if there is a hernia in levator ani
- The pudendal nerve is motor to the perineal muscles here and is supplied by S2-S4. It crosses behind the ischial spine. It is somatosensory to all of the perineum and the external genitalia.
- Sensation from the pudendal nerves are ABSOLUTELY SPECIFIC – can localise it well.
- This can be blocked - LA is useful for quick pain relief prior to instrumental delivery
Outline the process of episiotomy
E.g., episiotomy (60 degree angle from midline and sutured up postnatally) - not done prophylactically, usually done second stage of labour, done to avoid damage to the central structures (anal sphincter, perineal body - reduce pelvic floor dysfunction, muscles - reduce blood loss)
NOTE: we do episiotomy even if tears are better because the normal tears may go to the anus
Cut through perineal skin, bulbospongiosus, deep transverse perineal muscles
Done at 60 degrees angle to avoid bartholin’s glands and perineal body
Midline no longer recommended as it would damage the perineal body
Perineum
The perineum is the area between the vaginal opening and the anus
Anatomical borders
- Anterior: pubic symphysis
- Posterior: tip of the coccyx
- Laterally: inferior pubic rami and inferior ischial rami, and the sacrotuberous
- ligament
- Roof: pelvic floor
- Base: skin and fascia
Contents
Anal triangle: anal aperture, external anal sphincter muscle, ischioanal fossae ▪ Urogenital triangle
Perineal body
- Located at junction of urogenital and anal triangles
- Acts as a point of attachment for muscle fibres from the pelvic floor and the perineum itself
- In women, acts as a tear-resistant body between the vagina and the external anal sphincter, supporting the posterior part of the vaginal wall against prolapse
- Childbirth can lead to damage (stretching/tearing) of perineal body → can lead to possible prolapse of the pelvic viscera. This can be avoided by an EPISIOTOMY (a surgical cut in the perineum) → this causes damage to the vaginal mucosa but prevents uncontrolled tearing of the perineal body
The external genitalia
- The labia majora contain sebaceous and sweat glands
- There is a core of fatty tissue at the deepest part of each labium
- The labia minora divide anteriorly to form the prepuce and frenulum of the clitoris (clitoral hood)
- Posteriorly they divide to form the fourchette
- The labia minora contain sebaceous glands but no adipose tissue
- Both labia become engorged during sexual arousal
- The clitoris is made up of paired columns of erectile and vascular tissue called the corpora cavernosa
The vestibule is the cleft between the labia minora
- It contains openings of the urethra, Bartholin’s glands and the vagina
The vagina is surrounded by two bulbs of erectile and vascular tissue
Bartholin’s glands are bilateral and about the size of a pea
- They open via a 2 cm duct into the vestibule below the hymen and contribute to lubrication during intercourse
- can get infected to form Bartholin’s abscesses
The hymen is a thin covering mucous membrane across the entrance to the vagina
- It is usually perforated to allow menstruation
- It is ruptured during intercourse
- Any remaining tags are called carunculae myrtiformes
Cervix
Roughly 2.5 cm in length
Lateral to the cervix is the parametrium (connective tissue)
The ureters run 1 cm laterally to the supravaginal part of the cervix
Common site for malignancy (transformation zone)
Composed of two regions
- Ectocervix: portion projecting into vagina. The epithelium of the endocervix is columnar and ciliated in the upper 2/3. This will transition to squamous epithelium at the squamocolumnar junction
- Endocervical canal: proximal portion, lined by mucus-secreting simple columnar epithelium
Ovaries
The female gonads
Paired, oval organs attached to the posterior surface of the broad ligament of the uterus by the mesovarium (a fold of peritoneum, continuous with the outer surface of the ovaries)
- Neurovascular structures enter the hilum of the ovary via the mesovarium
The ovary is the only intra-abdominal structure that is NOT covered by peritoneum
Laterally, each ovary is attached to the suspensory ligament of the ovary with folds of
peritoneum that become continuous with the overlying psoas major
Anterior to the ovaries are the Fallopian tubes, superior portion of the bladder and the
uterovesical pouch
Posterior to the ovary is the ureter
Functions
- Produce oocytes
- Produce oestrogen and progesterone, in response to pituitary gonadotrophins
Size
- Size and appearance depends on age and stage of the menstrual cycle
- Proliferation of stromal cells in puberty makes them grow in size (reaching 3 cm long x 1.5 cm wide x 1 cm thick)
- The ovary becomes smaller after menopause
Components
- Surface: surface layer is formed by simple cuboidal epithelium, known as germinal epithelium
- Cortex: largely compromised of a connective tissue stroma; supports thousands of follicles; each primordial follicle contains an oocyte surrounded by a single layer of follicular cells
- Medulla: composed of supporting stroma and contains a rich neurovascular network which enters the hilum of the ovary from the mesovarium
At birth, most primordial follicles are found within the cortex
After puberty, some follicles become Graafian follicles and ovulate and become the corpus
luteum
This will ultimately undergo atresia and become the corpora albicans
Ligaments
- Two peritoneal ligaments attach to the ovary
- Suspensory ligament of ovary: fold of peritoneum extending from the
- mesovarium to the pelvic wall; contains neurovascular structures
- Ligament of ovary: extends from the ovary to the fundus of the uterus
Neurovascular supply
- Main arterial supply is via the paired ovarian arteries
- Arise directly from the abdominal aorta (inferior to renal arteries)
- There is also contribution from the uterine arteries
Venous drainage: paired ovarian veins
- Left drains into left renal vein
- Right drains directly into inferior vena cava
SNS and PNS innervation from ovarian and uterine (pelvic) plexuses respectively; the nerves reach the ovaries via the suspensory ligament of the ovary to enter the ovary at the hilum
Lymph drains into the para-aortic nodes
Polycystic ovaries: multiple small cysts which do not ovulate
Sometimes, you can get a large cyst
If < 4cm, usually do not cause any problems
If > 4cm, it may rupture, get infected, bleeding within cyst (haemorrhagic cyst), can cause ovarian torsion which can lead to necrosis
