1. APPLIED ANATOMY OF
PELVIS
AND
FETAL SKULL
DR. MOHD ASNIZAM ASARI
DEPARTMENT OF ANATOMY

2. 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

3. 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

4. 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

5. 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

6. HIP BONE
Ileum
Ischium
Pubis

7. 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)

8. HIP BONE: ISCHIUM
 Body of ischium
 Ramus of ischium
 Ischial spine
 Ischial tuberosity

9. 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

10. SACRUM
 Is made up of 5 fused vertebrae
 Triangular in shape
 Is divided into central mass and
lateral mass
Central
mass
Lateral
mass
Tranverse
ridge

11. SACRUM: ANTERIOR SURFACE
 Ala (wing)- upper part of
lateral mass
 4 anterior sacral foramina
 Sacral promontory
Ala Ala
Sacral promontory

12. SACRUM: POSTERIOR SURFACE
 Median sacral crest
 Posterior sacral foramina
 Sacral cornu (horn)
 Sacral hiatus
Sacral cornu
Sacral hiatus
Median crest
Sacral canal

13. 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
True
pelvis
False
pelvis

14. TRUE & FALSE PELVIS
True pelvis
False
pelvis
Abdominal
cavity

15. 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

16. 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

17. 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

18. 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

19.  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
MEASUREMENTS OF PELVIC INLET

20. Vaginal Examination to Determine
Diagonal Conjugate
Obstetric Conjugate = Subtracts 1.5 – 2.0 cm from Diagonal Conjugate

21. 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

22. MEASUREMENTS OF PELVIC OUTLET
• Three diameters of pelvic
outlet are usually described:
1) Anteroposterior
2) Transverse (intertuberous)
- can be estimated
3) Posterior sagittal
Pelvic outlet viewed from below
Sacrococcygeal joint

23. DIAMETER OF PELVIC OUTLET
Measurement Extension Diameter
Anteroposterior
diameter
From lower margin of pubic symphysis
→ sacrococcygeal joint
12.5 cm12.5 cm
Transverse
diameter
(intertuberous)
Between the ischial tuberosities
(Diameter > 8 cm – normal)
11 cm11 cm
The largest diameter of pelvic outlet = AP diameter

24. 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

25. 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

26. WALL OF PELVIC CAVITY
1) Anterior pelvic wall
2) Lateral pelvic wall
3) Posterior wall
4) Pelvic floor

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

28. 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

29. 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

30. 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

31. FEMALE MALE
• Bones are lighter, thinnerBones are lighter, thinner
• False pelvis is shallowFalse pelvis is shallow
• Pelvic cavity is wide & shallowPelvic cavity is wide & shallow
• Pelvic inlet round/ovalPelvic inlet round/oval
• Pelvic outlet comparatively largePelvic outlet comparatively large
• Subpubic angle largeSubpubic angle large
• Coccyx more flexible, straighterCoccyx more flexible, straighter
• Ischial tuberosities more evertedIschial tuberosities more everted
• Bones heavier, thickerBones heavier, thicker
• False pelvis is deepFalse pelvis is deep
• Pelvic cavity is narrow & deepPelvic cavity is narrow & deep
• Pelvic inlet heart-shaped + smallerPelvic inlet heart-shaped + smaller
• Pelvic outlet comparatively smallPelvic outlet comparatively small
• Subpubic angle more acuteSubpubic angle more acute
• Coccyx less flexible, more curvedCoccyx less flexible, more curved
• Ischial tuberosities longer, faceIschial tuberosities longer, face
more mediallymore medially

32. DIFFERENCES BETWEEN MALE & FEMALE
PELVIS

33. 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

34. 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

35. Pelvic
Variations
and
Abnormalities

36. PELVIC TYPES BASED ON CALDWELL-MALLOY
CLASSIFICATION
Note: Many pelvis are not
pure but mixed type. For
example – gynaecoid
pelvis with android
tendency

37. 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

38. 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

39. ANTHROPOID PELVIS
 Present in some males and females
 15% in Asian women; 15-30% in white women
 Pelvic inlet is long oval
 AP diameter > tranverse diameter
 Long & narrow sacrum
(often with 6 sacral segments)
 Straight pelvic sidewalls

40. 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

41. 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 %
NORMAL PELVIC VARIANTS

42. Normal Pelvic
Variations
Round inlet
Heart-shaped/
triangular inlet
Long oval inlet
Flat inlet

43. Which types of pelvic may
have difficulty to
accommodate the fetal
during delivery ?

44. FETAL SKULL

45. FETAL VS ADULT SKULL
TERM FETAL SKULL ADULT SKULL

46. THE SKULL
 Skull is divided into 2 parts:
1) Neurocranium:
Calvaria (skullcap)
Cranial base (basicranium)
2) Viscerocranium (Facial
skeleton)

47. 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

49. 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
Adult
Term Fetus

50. 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

51. 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

52. 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

53. 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)

54. 2 halves of frontal bone
are still separated by
suture
Orbit is
relatively large
Mandible is rudimentary
and still separated by
suture
Calvaria is relatively large
Facial skeleton is
relatively small

55. 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.

56. 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

57. Intermaxillary
sutures
Intermandibular sutures
SUTURES
Frontal suture

58. Coronal sutureSagittal suture
Lambdoid
suture

59. 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

60. 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

61.  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)

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

63. 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)

64. Anterior
fontanelle
Posterior fontanelle
Anterolateral
(sphenoid)
fontanelle
Posterolateral (mastoid)
fontanelle

65. 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

66. 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

67. 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

68. MOLDING OF FETAL SKULL
 Molding = adaptation of fetal head to the pelvic cavity
during birth
 To reduce head circumference

69. 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

70. THE END
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