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
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
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
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
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
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
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
48.
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.
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)
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