Pelvic anatomy Flashcards
Pelvic inlet (pelvic brim) boundaries
Posterior: sacral promontory
Anterior: pubic symphysis
Lateral: iliopectineal line
It is the boundary between the true and false pelvis
What vessels cross the pelvic inlet?
Ovarian vessels
Median sacral artery
Inferior mesenteric artery -> superior rectal artery
Pelvic outlet boundaries
Posterior: tip of coccyx
Anterior: pubic arch
Lateral: ischial tuberosity + sacrotuberous ligament
Border between pelvic cavity and perineum
What are the main differences between the male and female pelvis?
- Subpubic angle (M = <70 degrees; F = >8- degrees)
- Pelvic outlet (M = small; F = large)
- True pelvis (M = narrow, deep; F = wide, shallow)
Contents and boundaries of lesser (true) pelvis
Contents:
- True pelvic cavity
- Deep perineum
Boundaries:
- Pelvic surfaces of the hip bones
- Sacrum and coccyx
Attachments of the sacrotuberous ligament
From the sacrum to the ischial tuberosity
- Forms the sciatic notch border to make it a foramen
Attachments of the sacrospinous ligament
From the sacrum to the ischial spine
- Separates sciatic foramen into greater and lesser sciatic foramen
What are the four different shapes of the pelvic girdle?
Android - most common in males
Gynecoid - most common in females
Anthropoid - common, not good for child birth
Platypelloid - uncommon, not good for child birth
Differentiate between the true conjugate, obstetric conjugate and diagonal conjugate measurements
True: sacral promontory to superior border of pubic symphysis; 1.5cm less than diagonal conjugate
Obstetric: sacral promontory to middle of pubic symphysis, smallest diameter baby must pass through
Diagonal: sacral promontory to inferior aspect of pubic symphysis, estimate of obstetric
What is the plane of least dimensions?
It is the smallest part a baby must pass through
Boundaries:
- Anterior: lower border of pubic symphysis
- Posterior: lower border of sacrum
- Lateral: ischial spines
Obturator internus muscle
Lateral wall muscle, from pelvic surfaces of ilium, ischium and obturator membrane to greater trochanter of the femur.
Innervated by nerve to obturator internus (L5, S1, S2)
Piriformis muscle
Posterosuperior wall muscle, S2-S4 vertebrae to superior greater sciatic notch and sacrotuberous ligament
Innervated by anterior rami of S1 and S2
What are the muscles of the pelvic floor?
Coccygeus Levator ani: - Puborectalis - Pubococcygeus - Pubovaginalis - Iliococcygeus
Coccygeus muscle
Ischial spine to inferior coccyx
Innervated by S4 and S5
Individual functions of levator ani muscles
Pubococcygeus: main muscle
Iliococcygeus: elevates pelvic floor and anorectal canal
Puborectalis: maintains continence
Pubovaginalis: maintains urinary continence
Collective role of levator ani muscles and innervation
Collectively function to support pelvic viscera and resists increases in intra-abdominal pressure
Innervated by pudendal nerve (S2, S3, S4)
What is the broad ligament?
Double layer of peritoneum that connects the uterus to the lateral walls and floor of pelvis
3 parts:
- Mesometrium - extends laterally from uterus
- Mesosalpinx - drapes over the fallopian tubes
- Mesovarium - drapes over the ovaries
Contents of the broad ligament
Organs:
- Uterus
- Fallopian tubes
- Ovaries
Vessels:
- Ovarian artery
- Uterine artery
Ligaments:
- Ovarian ligament
- Round ligament of uterus
- Suspensory ligament of uterus
Pouches of the pelvic cavity
Males have 1, females have 2
Rectovesical pouch (males):
- Between rectum and bladder
- Most inferior part of the peritoneal cavity
Rectouterine pouch (females):
- Called the “Pouch of Douglas”
- Between rectum and uterus
- Most inferior part of peritoneal cavity - fluid accumulates here when erect
Vesicouterine pouch (females): - Between bladder and uterus
Somatic nervous supply to the peritoneum
Mostly derived from the sacral plexus (L4, L5, S1, S2, S3, S4) - most branches exit pelvis through greater sciatic foramen Main nerves: - Sciatic nerve (L4, L5, S1, S2, S3) - Pudendal nerve (S2, S3, S4) - Obturator nerve (L2, L3, L4) - Superior gluteal nerve - Inferior gluteal nerve
Function of sciatic nerve
- Posterior thigh muscles
- Sensory innervation of lower leg and foot
Course of pudendal nerve
Exits pelvis via greater sciatic foramen, re-enters via lesser sciatic foramen
Travels through pudendal canal
Function of pudendal nerve
Supplies:
- Pelvic floor muscles
- External urethral and anal sphincters
- Sensory innervation of perineum
Function of the obturator nerve
Motor and sensory innervation to the medial thigh
Superior gluteal nerve
Leaves pelvis via greater sciatic foramen (above piriformis), supplies gluteal region
Inferior gluteal nerve
Leaves pelvis via greater sciatic foramen (below piriformis), supplies gluteal region
What are the four routes through which autonomic nerves enter the pelvis?
- Sacral sympathetic trunks
- Peri-arterial plexuses
- Hypogastric plexuses
- Pelvic splanchnic nerves
Sacral sympathetic trunks (autonomic supply to pelvis)
- Continuation of lumbar sympathetic trunks
- Descend down the pelvic side of the sacrum
- Provide post-synaptic sympathetic fibres to sacral plexus for sympathetic innervation of lower limb
Peri-arterial plexuses (autonomic supply to pelvis)
- Supply the ovarian, superior rectal and internal iliac arteries
- Main function is vasomotion
Hypogastric plexuses (autonomic supply to pelvis)
There are superior and inferior hypogastric plexuses
Course of the superior hypogastric plexus
- Enters the pelvis and becomes right and left hypogastric nerves - these descend on anterior surface of the sacrum
- They merge with pelvic splanchnic nerves to become left and right inferior hypogastric plexuses
Inferior hypogastric plexuses function
Sympathetic fibres:
- Sacral splanchnic nerves provide fibres to pelvic vessels and structures
Parasympathetic fibres:
- Pelvic splanchnic nerves innervate all viscera below the splenic flexure
Pelvic splanchnic nerves (autonomic supply to pelvis)
- Arise from S2-S4 nerve roots
- Carry pre-synaptic parasympathetic fibres and visceral afferent fibres
General function of sympathetic and parasympathetic fibres in the pelvic region
Sympathetic:
- Mainly from lumbar splanchnic nerve
- Inhibit peristaltic movement of rectum
- Stimulates contraction of internal genital organs during orgasm
- Vasomotion
Parasympathetic:
- Mainly from pelvic splanchnic nerve
- Stimulate contraction of rectum and bladder
- Stimulate erections
Lymphatic drainage of the perineum
Testes/Ovaries - para-aortic lymph nodes
Superior rectum + sigmoid colon - para-rectal + inferior mesenteric lymph nodes
Scrotum, perianal skin, anal canal (below dentate line), skin of perineum + round ligament - superficial inguinal lymph nodes
Contents of the suprapiriform foramen
Superior gluteal a., v. and n.
Contents of the infrapiriform foramen
Internal pudendal a. and v.
Inferior gluteal a., v. and n.
Sciatic n.
Pudendal n.
Contents of the lesser sciatic foramen
Internal pudendal a. and v.
Pudendal n.
- Both are ENTERING the pelvis
Vascular supply to the pelvis
- Most comes from internal iliac artery
- Aorta -> common iliac @ L4 -> int/ext iliac @ L5/S1
- Internal iliac crosses the pelvic inlet and splits into anterior and posterior trunks at superior border of greater sciatic foramen
Anterior trunk of CIA divisions
9 divisions
REMEMBER: 3 to walls, 3 to bladder, 3 to viscera
Walls:
- Internal pudendal (terminal divisions are perineal artery, dorsal arteries of penis/clitoris)
- Inferior gluteal (supplies gluteus maximus, skin of buttocks)
- Obturator artery (through obturator canal)
Bladder:
- Umbilical (forms medial umbilical ligament)
- Superior vesical (supplies superior bladder)
- Inferior vesical (supplies inferior bladder)
Viscera:
- Uterine (supplies uterus, runs over ureter)
- Middle rectal (supplies distal rectum)
- Vaginal (supplies inferior bladder, vagina and rectum)
Posterior trunk of CIA divisions
Iliolumbar arteries
- Lumbar division: post. abdominal wall, psoas major
- Iliac division: iliac fossa
Lateral sacral arteries
- Piriformis, erector spinae, associated skin
Superior gluteal arteries
- Piriformis, all three gluteal muscles
Ovarian artery
- Branches off aorta inferior to renal arteries and superior to IMA
- Gives of ovarian and tubule branches
