Anatomy of the Pelvis
Amel Ibrahim MBBS BSc
www.iwanttobeasurgeon.blogspot.com
www.iwanttobeasurgeon.com
Amel.ibrahim@imperial.ac.uk
Contents
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Intro and definitions
Bones et al
Muscles
Vasculature
Lymphatics
Nerves
Organs
Special places
QUIZ
Preview
Further reading
Intro & Definitions
• Pelvic Brim (green line)
• Imagine a line drawn between
promontory of the sacrum,
arcuate line of the ilium,
pectineal line (pectin of pubis)
and pubic crest.
• Greater (False) pelvis
• All of the bony pelvis ABOVE
pelvic brim
• Lesser (True) pelvis
• All of pelvis BELOW pelvic
brim.
Bones et al
Bones
• Ilium (one on each side): crest,
anterior superior and inferior
iliac spines and greater sciatic
notch.
• Pubic bone (one on each side):
lesser sciatic notch, tubercle
and symphysis
• Ischium (one on each side):
lesser sciatic notch, spine and
tuberosity
• Sacrum: foramina for spinal
nerves
• Coccyx
More bones
• Vertebral column: 5
fused sacral and 3-5
fused coccygeal
vertebrae
• Ilium, pubic bone and
ischium meet to form
acetabulum for hip joint
• Obturator foramen
made by articulation of
ischium with pubic
bone
Ilium
Pubic
bone
Ischium
Ligaments
• Anterior longitudinal: runs
down entire vertebral column.
Prevents hyperflexion
• Inguinal ligament: arched
fibres of external oblique
• Pubic Symphysis: secondary
cartilaginous joint
• Sacroiliac joints anteriorly
• Posterior: sacrotuberous,
posterior sacrospinous and
sacrospinous
• Ligaments provide strengthand
stability of hip
Male Vs Female
Bones: pelvis taller, narrower and more compact. Evolutionary
optimised for bipedal locomotion. Acute angle between pubic rami (70
degrees).
Contents: rectum, bladder, prostate, anus and male reproductive organs
Bones: wider and broader with larger inlet. Optimised for childbirth
without compromising bipedal locomotion. Wide angle between pubic
rami (100 degrees). Wider acetabulum.
Contents: rectum, bladder, anus and female reproductive apparatus
Muscles
pubococcygeus
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Greater Pelvis:
Quadratus Lumborum: from iliac crest to insert into
12th rib and L1-4. Lateral flexor
Psoas Major: from lumbar veterbrae to lesser
trochanter of femur. Hip flexor.
Iliacus: from internal iliac fossa to lesser trochanter.
Joins with Psoas major = ILIOPSOAS (hip flexor and
trunk flexor)
Piriformis : from greater sciatic notch and anterior
sacrum to greater trochanter. Lateral rotator
Lesser Pelvis:
MUSCLES CONTROL SPHINCTERS
Diaphragm: pubococcygeus, coccygeus,
puborectalis, (pubovaginalis) and illiococcygeus
Levtor ani = a sling made by puborectalis, pubo- and
ilio-coccygeus. Prevents incontinence.
Sphincter urethrae
(Sphincter prostatae)
External anal sphincter
pubovaginalis elevates vagina
iliococcygeus
Psoas
major
iliacus
coccygeus
piriformis
Vasculature: Arteries
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Gonadal artery (branch of abdo aorta, origin L2)
Internal Iliac (anterior + posterior divisions):
Superior vesical
Inferior vesical (vaginal artery in female)
Middle and inferior rectal (superior rectal from
inferior mesenteric)
• Inferior and superior gluteal
• Uterine (uterus, vagina, ureter)
• Internal Pudendal (perineum, penis and urethra)
(from instant anatomy website)
veins
• Veins from pelvis follow arteries
• Drain to IVC (common iliac joins at L5)
• Left testicular drains to left renal not directly
into IVC
(From Instant anatomy)
lymphatics
• Lateral pelvic drain everything EXCEPT:
• Para aortic drain: gonad + fallopian tube +
uterus + ureter
• Inferior mesenteric drain: upper rectum
• All ultimately drain into lymphatic duct and
cisterna chyli
Nerves
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Dermatomes: T12 (suprapubic), L1
(groin), L2 (upper thigh), S1, 2, 3, 4, 5
(buttocks, perineal and perianal). S1,
2 (genitals).
Sympathetic: from lumbo-sacral
trunk (L1-S5).
Parasympathetic: S2-4
Lumbar plexus: L1-5 roots lie on
Psoas M. Branches:
– 3 lateral to Psoas (lateral cutaneous
nerve, iliohypogastric, ilioinguinal and
– 1 anterior to Psoas: genitofemoral
– 2 medial to psoas: femoral, obturator
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Sacral Plexus: S1-4
Pudendal: S2-4. mixed
sensory/autonomic
Coccygeal
Dermatomes
Autonomic
Sympathetic
Parasympathetic
• Hypogastric nerves:
preganglionic fibres travel to
hypogastric plexus and
synapse there then travel to
viscera as hypogastric nerves.
• Sacral splanchnic nerves:
fibres synapse at sympathetic
chain and postganglionic fibres
travel to hypogastric plexus as
a splanchnic nerve.
• Pudendal nerve: mixed
autonomic and sensory. S2-4
• Pelvic splanchnic nerves:
preganglionic fibres from S2-4
travel to hypogastric plexus ad
from there nerves travel to
and synapse at viscera.
• Cause erection and sphincter
relaxation for
micturition/defaecation
Divisions of Lumbar plexus
lateral cutaneous nerve: sensory to
lateral thigh
Iliohypogastric: motor to transversus
and internal oblique, sensory to mon
pubis
Ilioinguinal: motor to internal oblique,
transversus and conjoint tendon.
Sensory to upper medial thigh, labia
majora, scrotum and root of penis
Genitofemoral: motor to cremaster.
Sensory to scrotum, anterior thigh,
spermatic fascia and tunica vaginalis.
Femoral (L2,3,4): motor to iliacus,
pectineus and quadriceps femoris.
Sensory to anterior thigh.
Obturator :
Sacral Plexus
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Formed by L4, 5, S1-5
Lies on piriformis
Branches:
6 nerves from sacral roots
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Anterior division:
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Nerve to piriformis
Posterior femoral
Perforating cutaneous
Perineal branch to levator ani
Pelvic splanchnic
Pudendal
Nerve to Quadratus femoris
Nerve to Obturator internus
Tibial branch of sciatic nerve
Posterior division:
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Superior gluteal
Inferior gluteal
Common peroneal branch of sciatic nerve
Pudendal Nerve
• Somatic and autonomic
• Origins S2-4
• Exits through greater sciatic
foramen and re-enters pelvis
via lesser sciatic foramen
• Travels with pudendal vessels
along ischiorectal fossa in
Alcock’s canal
• Supplies sphincters and
genitalia via perineal, dorsal
root of penis/clitoris and
inferior anal nerves
• Promotes ejaculation, sexual
arousal, anal and bladder
sphincter control.
Coccygeal Nerve
• 31st spinal nerve
• Forms coccygeal plexus
with S5
• Coccygeal plexus gives
rise to annococcygeal
nerve which supplies
sacroccygeal joint and
skin over coccyx.
Organs
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RENAL TRACT:
Ureters:
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Originate at renal hilum at L2
Path initially medial to vertebrae and at pelvic
brim take infero-posterior path
Oblique entry into bladder avoids urinary
reflux
Crossed by gonadal artery in pelvis
Posterior to it are psoas and genitofemoral
nerve
Under it are uterine artery and vas deferens
Arterial supply via gonadal, renal, vesical,
vaginal and aortic branches
Autonomic innervation
Bladder:
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Trigonal structure.
Wall has 3 layers of smooth muscles: inner
circular and middle/outer longitudinal layers
Arterial supply from superior and inferior
vesicalnerves: sympathetic closes bladder
neck whilst parasympathetic relaxes detrusor
muscle to allow for miturition
Rectum and anus
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Rectum
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Columnar epithelium
Superior 1/3 covered by peritoneum
anteriorly and laterally, middle 1/3 anterior
peritoneum only and inferior 1/3 bare
Arteries: superior rectal from inferior
mesenteric and middle rectal from internal
iliac +inferior rectal from pudendal artery
Veinous drainage from internal venous plexus
which drains to:
superior rectal which then drains to inferior
mesenteric vein, middle rectal which drains to
internal iliac vein and inferior rectal vein
which drains into pudendal vein
Anus:
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Starts at anorectal junction aka dentate line
Squamous epithelium continuous with skin
gradually transforming to columnar as rectum
approached
External anal sphincter is skeletal muscle with
somatic innervation thus voluntary
Internal anal sphincter is smooth muscle and
under autonomic control
Female pelvic viscera
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Uterus:
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Ovaries:
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Run in free edge of broad ligament
Ovarian and uterine arteries
Vagina:
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Attached to posterior aspect of broad ligament
Ovarian artery
Right ovarian vein drains to IVC whilst left to left renal vein
Sympathetics from aortic plexus and parasympathetics from
pelvic plexus
Fallopian tubes:
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Held at lateral walls by double fold of peritoneum aka broad
ligament
Uterine artery
Sympathetic and parasympathetic innervation from pelvic
plexus
Venous plexus drain to rectal and vesical veins
Opens into vaginal vestibule
Vaginal artery
Sympathetic supply from pelvic plexus and somatic sensory
innervation from ilioinguinal and pudendal nerves
Venous drainage from pelvic floor plexus to internal iliac
Clitoris:
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Female equivalent of penis
Nerve supply via pudendal
Male pelvic viscera
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Scrotum:
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Testis:
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Testicular (gonadal artery)
pampiniform plexus drain to testicular veins
Testicular vein drains to IVC on right and left renal artery on left
Prostate:
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layers are skin, dartos muscle, external spermatic fascia, cremaster
muscle, internal spermatic fascia, tunica vaginalis and tunica
albuginea
Multi-lobar (5) with posterior groove. Apex at the bottom and
base at top
Smooth muscle
Entered by the vasa deferens and seminal vesicals
Contains prostatic urethra
Arterial supply from inferior vesical, middle rectal and occasionally
pudendal arteries
Drains to venous plexus and then to internal iliac vein
Sympathetic nerves promote ejaculation and smooth muscle
contraction whilst parasympathetics promote erection
Penis and Urethra:
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Pre-prostatic, prostatic, membranous and penile urethra
Receives ejaculatory ducts, bulbourethral and urethral glands
Arterial supply from urethral artery, deep artery to penis and
dorsal artery of penis
Drainage via superficial and deep dorsal veins of penis
Nerves are sympathetic and parasympathetics for ejaculation and
erection. Sensory supply to skin and glans of penis from pudendal
nerve
Special places
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Inguinal canal:
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Alcock’s canal:
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4 cm long running from Anterior superior iliac spine and pubic tubercle.
Contains spermatic cord (or round ligament) and ilioinguinal nerve.
Spermatic cord contains: 3 structures (vas deferens, cremaster muscle and pampiniform plexus), 3 arteries (artery to vas, artery
to cramster and testicular artery) and 3 nerves (sympathetic, parasympathetic and genitofemoral)
Floor: fibres of external oblique = inguinal ligament
Roof: transversus abdominis and internal oblique
Anterior: external oblique and internal oblique
Posterior: transversalis fascia and conjoint tendon
Where pudendal nerve, vein and inetrnal pudendal artery run.
Formed by obturator internus fascia
Runs on the lateral wall of ischiorectal fossa
Femoral canal:
Contains lymphatic vessels and cloquet’s lymph node
Anterior border is inguinal ligament
Posterior border is pectineal ligament
Medial border is lacunar ligament
Lateral border is femoral vein
Site of bowel herniation
Pubic tubercle:
Herniae above ad medial are inguinal and those below and lateral are femoral
Quiz
Q1) On the bony pelvis:
• A) true pelvis lies between iliac crests T/F
• B) the acetabulum formed by contributions from
all parts of hip bone T/F
• C) male pelvic inlet more oval than female in
shape T/F
• D) angle between pubic rami wider in male T/F
• E) pelvic out let is between symphysis pubis and
sacral tuberosity T/F
Quiz
Q1) On the bony pelvis:
• A) true pelvis lies between iliac crests T/F
• B) the acetabulum formed by contributions from
all parts of hip bone T/F
• C) male pelvic inlet more oval than female in
shape T/F
• D) angle between pubic rami wider in male T/F
• E) pelvic out let is between symphysis pubis and
sacral tuberosity T/F
Q2) Levator Ani
• A) has fibres which assist continence by
pulling rectum backwards T/F
• B) lies inferior to ischiorectal fossa T/F
• C) is supplied by anterior rami of S1-2 T/F
• D) Contracts during defaecation T/F
Q2) Levator Ani
• A) has fibres which assist continence by
pulling rectum backwards T/F
• B) lies inferior to ischiorectal fossa T/F
• C) is supplied by anterior rami of S1-2 T/F
• D) Contracts during defaecation T/F
Q3) On sphincters of the anus
• A) the anus contains longitudinal and circular
muscle T/F
• B) External sphincter composed of involuntary
muscle T/F
• C) external sphincter continuous with muscle
of rectum T/F
Q3) On sphincters of the anus
• A) the anus contains longitudinal and circular
muscle T/F
• B) External sphincter composed of involuntary
muscle T/F
• C) external sphincter continuous with muscle
of rectum T/F
• Q4) on the inguinal canal:
• A) contains spermatic cord and splanchnic
nerve T/F
• B) posterior border is transversus abdominis
and internal oblique T/F
• C) floor is inguinal ligament T/F
• D) carries round ligament in females T/F
• Q4) on the inguinal canal:
• A) contains spermatic cord and splanchnic
nerve T/F
• B) posterior border is transversus abdominis
and internal oblique T/F
• C) floor is inguinal ligament T/F
• D) carries round ligament in females T/F
Q5) on origins of nerves
• A) lumbar plexus from L1-5 T/F
• B) pudendal arises from S2-4 T/F
• C) parasympathetic plexus arises from S2-4 T/F
• D) hypogastric nerves carry postganglionic
fibres T/F
Q5) on origins of nerves
• A) lumbar plexus from L1-5 T/F
• B) pudendal arises from S2-4 T/F
• C) parasympathetic plexus arises from S2-4 T/F
• D) hypogastric nerves carry postganglionic
fibres T/F
Preview
Fin
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Useful books:
Instant anatomy: good for surface anatomy, blood vessels and nerves
Netter’s atlas
(Anatomy recall)
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Websites:
www.iwanttobeasurgeon.com (down for construction at present)
www.iwanttobeasurgeon.blogspot.com
www.instantanatomy.net
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Apps:
Gray’s anatomy (2 quid!)
Netter’s flash cards (twenty pounds but useful for revision on tube)
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DVD:
Acland’s (AMAZING and free from Warwick University website or youtube. £130 for DVD set)
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Exam Material:
Pastest has over 800 anatomy questions and even more useful when you sit finals Have to pay though :(
http://ect.downstate.edu/courseware/haonline/quiz/practice/u7/quiztop7.htm (excellent for uestions on
cadaveric dissections)