Anatomy of the Pelvis

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Anatomy of the Pelvis

• Amel Ibrahim MBBS BSc
• www.iwanttobeasurgeon.blogspot.com
• www.iwanttobeasurgeon.com
• Amel.ibrahim_at_imperial.ac.uk

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Contents

• Intro and definitions
• Bones et al
• Muscles
• Vasculature
• Lymphatics
• Nerves
• Organs
• Special places
• QUIZ
• Preview
• Further reading

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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.

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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

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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
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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

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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

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Muscles
pubococcygeus

• 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
coccygeus
Psoas major
piriformis
iliacus
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Vasculature Arteries

• 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)

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(from instant anatomy website)
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veins

• Veins from pelvis follow arteries
• Drain to IVC (common iliac joins at L5)
• Left testicular drains to left renal not directly
  into IVC

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(From Instant anatomy)
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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

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Nerves

• 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
• Sacral Plexus S1-4
• Pudendal S2-4. mixed sensory/autonomic
• Coccygeal

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Dermatomes
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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

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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

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Sacral Plexus

• Formed by L4, 5, S1-5
• Lies on piriformis
• Branches
• 6 nerves from sacral roots
• Nerve to piriformis
• Posterior femoral
• Perforating cutaneous
• Perineal branch to levator ani
• Pelvic splanchnic
• Pudendal
• Anterior division
• Nerve to Quadratus femoris
• Nerve to Obturator internus
• Tibial branch of sciatic nerve
• Posterior division
• Superior gluteal
• Inferior gluteal

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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 Alcocks 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.

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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.

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Organs

• RENAL TRACT
• Ureters
• 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
• 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

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Rectum and anus

• Rectum
• 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
• 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

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Female pelvic viscera

• Uterus
• 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
• Ovaries
• 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
• Run in free edge of broad ligament
• Ovarian and uterine arteries
• Vagina
• Opens into vaginal vestibule
• Vaginal artery
• Sympathetic supply from pelvic plexus and somatic
  sensory innervation from ilioinguinal and
  pudendal nerves

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Male pelvic viscera

• Scrotum
• layers are skin, dartos muscle, external
  spermatic fascia, cremaster muscle, internal
  spermatic fascia, tunica vaginalis and tunica
  albuginea
• Testis
• Testicular (gonadal artery)
• pampiniform plexus drain to testicular veins
• Testicular vein drains to IVC on right and left
  renal artery on left
• Prostate
• 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
• Pre-prostatic, prostatic, membranous and penile
  urethra

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Special places

• Inguinal canal
• 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
• Alcocks canal
• 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 cloquets lymph
  node
• Anterior border is inguinal ligament
• Posterior border is pectineal ligament
• Medial border is lacunar ligament
• Lateral border is femoral vein

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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

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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

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• 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

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• 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

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• 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

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• 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

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• 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

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• 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

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• 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

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• 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

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Preview
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Fin

• Useful books
• Instant anatomy good for surface anatomy, blood
  vessels and nerves
• Netters atlas
• (Anatomy recall)
• Websites
• www.iwanttobeasurgeon.com (down for construction
  at present)
• www.iwanttobeasurgeon.blogspot.com
• www.instantanatomy.net
• Apps
• Grays anatomy (2 quid!)
• Netters flash cards (twenty pounds but useful
  for revision on tube)
• DVD
• Aclands (AMAZING and free from Warwick
  University website or youtube. 130 for DVD set)
• Exam Material
• Pastest has over 800 anatomy questions and even
  more useful when you sit finals Have to pay
  though (