Applied Anatomy of Female Pelvis & Fetal Skull

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APPLIED ANATOMY OF PELVIS AND FETAL SKULL
DR MALLESWAR RAO KASINA
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OBJECTIVES

• To learn about
• 1) Applied anatomy of female pelvis
• - Basic anatomy
• - Classification
• - Pelvic inlet outlet
• - Pelvic measurement
• - Variation in pelvis
• 2) Fetal/newborn skull
• - Features of fetal/newborn skull
• - Sutures fontanelles

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BONY PELVIS

• Bony pelvis is formed by
• 1) 2 Hip bones
• formed by fusion of 3 bones ilium, ischium and
  pubis
• 2) Sacrum
• formed by fusion of 5 sacral vertebrae
• 3) Coccyx
• formed by fusion of 4-5 coccygeal vertebrae
• Pelvic girdle hip bones sacrum

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FUNCTIONS OF BONY PELVIS
1) To protect pelvic viscera 2) To support the
weight of the body - transfer the weight of the
upper body from the axial to the lower
appendicular skeleton 3) Provides attachment for
muscles 4) In females, it provide bony support
for the birth canal
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HIP BONE

• 2 hip bones are joined at the pubic symphysis
• Hip bones articulate with the sacrum at the
  sacroiliac joints
• Ilium, ischium and pubis fused at acetabulum

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HIP BONE
Ileum
Pubis
Ischium
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HIP BONE ILIUM

• Ala of ileum
• Body of ileum
• Iliac crest
• Iliac fossa
• Anterior superior iliac spine (ASIS)
• Anterior inferior iliac spine (AIIS)
• Posterior superior iliac spine (PSIS)
• Posterior inferior iliac spine (PIIS)

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HIP BONE ISCHIUM

• Body of ischium
• Ramus of ischium
• Ischial spine
• Ischial tuberosity

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HIP BONES PUBIS

• Body of pubis
• Superior ramus of pubis
• Inferior ramus of pubis
• Pubis crest
• Pubic tubercle
• Pecten pubis (pectineal line of
  pubis)
• Subpubic angle

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SACRUM

• Is made up of 5 fused vertebrae
• Triangular in shape
• Is divided into central mass and lateral mass

Lateral mass
Central mass
Tranverse ridge
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SACRUM ANTERIOR SURFACE
Sacral promontory

• Ala (wing)- upper part of lateral mass
• 4 anterior sacral foramina
• Sacral promontory

Ala
Ala
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SACRUM POSTERIOR SURFACE
Sacral canal

• Median sacral crest
• Posterior sacral foramina
• Sacral cornu (horn)
• Sacral hiatus

Median crest
Sacral cornu
Sacral hiatus
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CLASSIFICATION OF PELVIS

• Divided into
• 1) False pelvis (pelvis major greater pelvis)
• Part of abdominal cavity
• 2) True pelvis (pelvis minor lesser pelvis )
• Is the true pelvic cavity
• Lies inferior to pelvic brim/pelvic inlet

False pelvis
True pelvis
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TRUE FALSE PELVIS
False pelvis
Abdominal cavity
True pelvis
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APERTURES OF TRUE PELVIS

• Pelvic inlet ( pelvic brim)
• also called superior pelvic aperture
• Pelvic outlet
• also called inferior pelvic aperture
• closed by the pelvic diaphragm

Pelvic inlet
Pelvic outlet
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PELVIC INLET

• Pelvic inlet is bounded by
• 1. Superior margin of pubic symphysis
• 2. Pubic crest
• 3. Iliopectineal line
• 4. Anterior border of ala of sacrum
• 5. Sacral promontory

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MEASUREMENTS OF PELVIC INLET

• Four diameters of pelvic inlets
• 1) Anteroposterior (true conjugate)
• 2) Diagonal conjugate
  can be measured clinically
• 3) Obstetric conjugate
• 4) Transverse diameter

Transverse
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DIAMETER OF PELVIC INLET
Measurement Extension Diameter
Anterior-posterior ( True conjugate ) From the sacral promontory ? superior margin of pubic symphysis 11.5 cm
Diagonal conjugate Sacral promontory ? inferior margin of the pubic symphysis 12.0 cm
Obstetric conjugate Sacral promontary ? nearest point on posterior surface of pubic symphysis 10.5 cm
Transverse diameter The widest distance across pelvic brim 13.5 cm
The largest diameter of pelvic inlet Transverse
diameter
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MEASUREMENTS OF PELVIC INLET

• Obstetric conjugate is clinically important It
  is shortest AP diameter through which the
  head must pass. But cannot
  be measured clinically
• Diagonal diameter can be measured clinically
• For clinical purposes, obstetric conjugate is
  estimated indirectly by subtracting
  1.5 to 2 cm from diagonal conjugate

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Vaginal Examination to Determine Diagonal
Conjugate
Obstetric Conjugate Subtracts 1.5 2.0 cm from
Diagonal Conjugate
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PELVIC OUTLET

• Diamond shaped
• Is bounded by
• 1) Inferior margin of the pubic symphysis
• 2) Inferior rami of the pubis
• 3) Ischial tuberosities
• 3) Sacrotuberous ligaments
• 4) Tip of coccyx

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MEASUREMENTS OF PELVIC OUTLET

• Three diameters of pelvic outlet are usually
  described
• 1) Anteroposterior
• 2) Transverse (intertuberous)
• - can be estimated
• 3) Posterior sagittal

Sacrococcygeal joint
Pelvic outlet viewed from below
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DIAMETER OF PELVIC OUTLET
Measurement Extension Diameter
Anteroposterior diameter From lower margin of pubic symphysis ? sacrococcygeal joint 12.5 cm
Transverse diameter (intertuberous) Between the ischial tuberosities (Diameter gt 8 cm normal) 11 cm
The largest diameter of pelvic outlet AP
diameter
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ROTATION OF FETAL HEAD

• Widest diameter of pelvic canal changes from
  transverse diameter at pelvic inlet to AP
  diameter at pelvic outlet
• To obtain best fit of fetal head, the longest
  diameter of the fetal head passes through the
  widest diameter of the pelvis. Therefore the head
  must rotate during labour

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WALL OF PELVIC CAVITY

• The wall of the true pelvis is formed by
• Anteriorly by pubic symphasis, body of pubis,
  pubic rami , rami of ischium and obturator
  membrane
• Laterally by ischial bone sacrosciatic
  ligaments
• Posteriorly by sacrum coccyx

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WALL OF PELVIC CAVITY

• 1) Anterior pelvic wall
• 2) Lateral pelvic wall
• 3) Posterior wall
• 4) Pelvic floor

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PELVIC FLOOR

• Pelvic floor is formed by pelvic diaphragm which
  is composed of
• 1) Levator ani
• Puborectalis
• Pubococcygeus
• Iliococcygeus
• 2) Coccygeus (Ischiococcygeus)

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LEVATOR ANI MUSCLE

• Contraction of levator ani muscles raises the
  entire pelvic floor
• Functions
• 1) Control of urination defecation
• Relaxation of levator ani muscle allow urination
  defecation to occur
• 2) Support for viscera (eg. uterus, bladder)
• 3) Helps direct fetal head toward birth canal at
  parturition

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LEVATOR ANI INJURY

• Levator ani muscle often stretch and can be
  injured during childbirth
• Of these, pubococcygeus muscle is more commonly
  damage
• These injuries may predispose women to greater
  risk of pelvic organ prolapse and urinary
  incontinence

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MALE VS FEMALE PELVIS

• There are a large number of differences between
  male and female pelvis. These differences are
  basically related to 2 factors
• 1) In male - the heavier build and stronger
  muscles in the males accounting for the stronger
  bone structure and better defined muscle markings
• 2) In females - comparatively wider and
  shallower pelvic cavity in female correlated with
  its role as bony part of the birth canal

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FEMALE MALE

• Bones are lighter, thinner
• False pelvis is shallow
• Pelvic cavity is wide shallow
• Pelvic inlet round/oval
• Pelvic outlet comparatively large
• Subpubic angle large
• Coccyx more flexible, straighter
• Ischial tuberosities more everted

• Bones heavier, thicker
• False pelvis is deep
• Pelvic cavity is narrow deep
• Pelvic inlet heart-shaped smaller
• Pelvic outlet comparatively small
• Subpubic angle more acute
• Coccyx less flexible, more curved
• Ischial tuberosities longer, face more medially

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DIFFERENCES BETWEEN MALE FEMALE PELVIS
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VARIATIATION OF PELVIC SHAPE

• Female pelvis shapes may be subdivided as follows
  (after Caldwell and Moloy)
• 1. Normal and its variants
• - Gynaecoid most common type , suited for
  delivery
• - Android the masculine type of pelvis
• - Platypelloid flat pelvis short AP diameter
  wide transverse
  diameter
• - Anthropoid resembling that of anthropoid
  ape, AP diameter is greater than the transverse
• 2. Symmetrically contracted pelvis
• - That of a small women but with a symmetrical
  shape

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• 3. Rachitic pelvis
• - This deformity is caused by rickets (due to
  Vit D deficiency)
• - Sacrum is rotated so that the sacral
  promontory projects forward and coccyx tips
  backward
• - AP diameter of inlet is therefore narrowed but
  the outlet is increased
• 4. Asymmetrical pelvis
• - Asymmetry pelvis can be due to variety of
  causes such as scoliosis, poliomyelitis, pelvic
  fracture, congenital abnormality due to
  thalidomide etc

Rachitic pelvis
Asymmetrical pelvis
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Pelvic Variations and Abnormalities
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Pelvic Types Based On Caldwell-Malloy
Classification
Note Many pelvis are not pure but mixed type.
For example gynaecoid pelvis with android
tendency
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GYNAECOID PELVIS

• Is a typical female pelvis. Ideal for vaginal
  delivery
• Found in 80 of Asian women 50-70 white women
• Rounded or slightly oval inlet
• Straight pelvic sidewalls with roomy pelvic
  cavity
• Ischial spines are not prominent
  - wide
  interspinous diameter
• Good sacral curve
• Subpubic arch is wide

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ANDROID PELVIS

• Present in most male and also in few females
• 0.6 in Asian women 2-8 in white women
• Heart shaped (or triangular) pelvic inlet - due
  to prominent sacrum
• Pelvis funnels from above downwards (convergent
  sidewalls)
• Prominent ischial spines
• Sacrum inclining forward
• Narrow subpubic arch

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ANTHROPOID PELVIS

• Present in some males and females
• 15 in Asian women 15-30 in white women
• Pelvic inlet is long oval
• AP diameter gt tranverse diameter
• Long narrow sacrum
  (often with 6
  sacral segments)
• Straight pelvic sidewalls

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PLATYPELLOID PELVIS

• Uncomon in both sexes
• 6 of Asian women 8-13 in white women
• Pelvic inlet appears slightly flattened (kidney
  shape)
• Transverse diameter is greater than AP diameter
• Sacral promontory pushed forwards
• Straight pelvic sidewalls
• Subpubic angle
  interspinous
  diamater
  are wide

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Normal Pelvic Variants
Gynaecoid Android Anthropoid Platypelloid
Shape of inlet Round Heart-shaped / triangular Long oval Flat
Sacrosciatic notch Wide Narrow Wide Narrow
Side walls Straight Convergent Straight Straight
Ischial spine Not prominent Prominent Not prominent Not prominent
Subpubic angle Wide Narrow Medium Wide
Incidence in Asian women 80 0.6 15 6
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Normal Pelvic Variations
Round inlet
Heart-shaped/ triangular inlet
Long oval inlet
Flat inlet
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Which types of pelvic may have difficulty to
accommodate the fetal during delivery ?
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FETAL SKULL
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FETAL VS ADULT SKULL
TERM FETAL SKULL
ADULT SKULL
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THE SKULL

• Skull is divided into 2 parts
• 1) Neurocranium
• Calvaria (skullcap)
• Cranial base (basicranium)
• 2) Viscerocranium (Facial skeleton)

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REGIONS OF FETAL SKULL

• Regions of the fetal skull have been designated
  to aid in the description of the presenting part
  felt at vaginal examination during labour
• Occiput the area lying behind posterior
  fontanelle
• Vertex the area between anterior and posterior
  fontanelles and between parietal eminences
• Bregma area around anterior fontanelle
• Sinciput area lying in front of anterior
  fontanelle. This is subdivided into 2 part the
  brow and the face
• Brow area between anterior fontanelle and root
  of the nose
• Face area below the root of the nose

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FETAL SKULL

• Skull of a term fetus or newborn infant is
  disproportionately large compared with other
  parts of the skeleton
• Facial skeleton is relatively small compared to
  that in adult and calvaria is relatively large

Term Fetus
Adult
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FACIAL SKELETON OF TERM FETUS

• Facial skeleton is relatively small
• In adult, facial skeleton forms 1/3 of the skull
  but in the newborn, facial skeleton only forms
  1/8 of the skull
• Smallness of the face is due to
• rudimentary development of the maxillae, mandible
  and paranasal sinuses
• absence of erupted teeth
• the small size of the nasal cavities
• Nose lies almost entirely between the
  orbits
• Orbits appears relatively large

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CALVARIA OF TERM FETUS

• Calvaria is relatively large
• At birth, the bones of the calvaria are smooth
  and unilaminar ( no diploë is present)
• Bones of calvaria do not fuse
• Have fibrous sutures between bones
• At birth, frontal and parietal eminences are
  prominent

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OTHER CHARACTERISTICS OF FETAL SKULL

• Other characteristics of a term fetal skull
• 1) Mastoid proces is absent
• Mastoid process forms during the 1st year as
  sternocleidomastoid muscles complete their
  development and pull on the petromastoid parts of
  the temporal bones
• 2) Styloid process is absent
• 3) Stylomastoid foramen is exposed on the
  lateral surface of the skull (facial nerve is
  vulnerable to injury)
• 4) Glabella and superciliary arches are not
  developed

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5) Paranasal sinuses are rudimentary or absent -
only maxillary sinus are usually identifiable.
Frontal sinus is absent 6) External acoustic
meatus is short, straight and wholly
cartilagenous 7) Ossification is incomplete
many bones are still in several pieces united by
fibrous tissue or cartilage - frontal bone is in
2 halves joined by metopic suture - mandible is
in 2 halves - occipital bone is in 4 parts
(squamous, lateral and basilar parts of occipital
bone are all separate)
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Calvaria is relatively large
2 halves of frontal bone are still separated by
suture
Orbit is relatively large
Facial skeleton is relatively small
Mandible is rudimentary and still separated by
suture
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SUTURES

• Sutures fibrous joint between flat bones of
  calvaria
• Sutures allow the bones to move during the birth
  process (moulding)
• Sutures allows brain to enlarge during infancy
  and childhood.

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SUTURES
Important sutures 1) Metopic (frontal) suture
2) Sagittal suture 3) Coronal suture 4)
Lambdoidal suture 5) Squamous suture 6)
Intermaxillary suture 7) Intermandibular
sutures
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SUTURES
Frontal suture
Intermaxillary sutures
Intermandibular sutures
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Coronal suture
Sagittal suture
Lambdoid suture
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CLOSURE OF SUTURES

• Cranial sutures starts to ossify by age of 8
• Sutures on facial skeleton ossify earlier.
  Example- metopic sutures closes as early as 3
  months of age (between 3-9 months)
• Obliteration (union of bone) of cranial sutures
  progresses with age, usually starting between 20
  to 30 years , often before the age of 40
• Obliteration usually begins in the coronal
  suture, and then extends into sagittal and
  lambdoid sutures

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CRANIOSYNOSTOSIS

• Craniosynostosis premature fusion
  of cranial
  sutures (by ossification)
• This premature sutural closure change the growth
  pattern of the skull.
• Because skull cannot expand perpendicular to the
  fused suture, it compensates by growing more in
  other direction perpendicular to the open
  sutures. The resulting growth pattern provides
  the necessary space for the growing brain, but
  results in an abnormal head shape and sometimes
  abnormal facial features
• In cases in which the compensation does not
  effectively provide enough space for the growing
  brain, craniosynostosis results in increased
  intracranial pressure

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• Types of craniosynostosis
• 1) Scaphocephaly (boat head)
• - due to premature closure of sagittal suture
• 2) Brachycephaly (short head)
• - premature closure of coronal suture on both
  sides (bilaterally)
• 3) Plagiocephaly (asymmetry head)
  - due to unilateral
  closure of coronal suture (or lambdoid suture)

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• 4) Trigonocephaly (triangular head)
• - premature closure of metopic suture
• 5) Pansynostosis
• - premature closure of multiple suture

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FONTANELLES

• Fontanelle Areas of fibrous tissue membrane
  separating the bones of the calvaria
• Major fontanelles
• 1) Anterior
• 2) Posterior
• 3) Anterolateral (Sphenoidal)
• 4) Posterolateral (Mastoid)

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Posterior fontanelle
Anterior fontanelle
Anterolateral (sphenoid) fontanelle
Posterolateral (mastoid) fontanelle
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ANTERIOR FONTANELLE

• Diamond or rhomboid in shaped
• Located at the junction of the sagittal, coronal
  and frontal sutures
• The future site of bregma
• Is closed (ossify) by 18 months of age

Anterior fontanelle
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POSTERIOR FONTANELLE

• Triangular in shape
• Located at the junction of the lambdoid and
  sagittal sutures
• The future site of lambda
• Begins to close during first 2 to 3 months after
  birth

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CLINICAL USE OF FONTANELLES

• During vaginal examination (during birth)
• To indicate in which direction the occiput is
  pointing
• The degree of flexion or extension of the head
• Degree of hydration
• Level of intracranial pressure
• To obtain blood sample from underlying superior
  sagittal sinus
• Progress of growth of the frontal and parietal
  bones

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MOLDING OF FETAL SKULL

• Molding adaptation of fetal head to the pelvic
  cavity during birth
• To reduce head circumference

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MOULDING

• During the passage though the birth
  canal, the head can be squeezed
  because of slight movement at
  the fontanelle sutures and
  slight overriding of
  bones also occur
• Frontal bones slip under parietal bones
• Parietal bones override each other
• Occipital bone slip under the parietal bones
• The resilience of the bones of the fetal skull
  allows it to resist forces that would produce a
  fracture in adults

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