APPLIED ANATOMY OF PELVIS

AND FETAL SKULL

DR. MOHD ASNIZAM ASARIDEPARTMENT OF ANATOMY

OBJECTIVESTo 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

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

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

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

HIP BONE

Ileum

Ischium

Pubis

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)

HIP BONE: ISCHIUM

Body of ischium Ramus of ischium Ischial spine Ischial tuberosity

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

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

SACRUM: ANTERIOR SURFACE

Ala (wing)- upper part of lateral mass

4 anterior sacral foramina

Sacral promontory

Ala Ala

Sacral promontory

SACRUM: POSTERIOR SURFACE

Median sacral crest

Posterior sacral foramina

Sacral cornu (horn)

Sacral hiatus

Sacral cornu

Sacral hiatus

Median crest

Sacral canal

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

TRUE & FALSE PELVIS

True pelvis

False pelvis

Abdominal cavity

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

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

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

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

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

Vaginal Examination to Determine Diagonal Conjugate

Obstetric Conjugate = Subtracts 1.5 – 2.0 cm from Diagonal Conjugate

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

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

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

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

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

WALL OF PELVIC CAVITY

1) Anterior pelvic wall

2) Lateral pelvic wall

3) Posterior wall

4) Pelvic floor

PELVIC FLOOR

Pelvic floor is formed by pelvic diaphragm which is composed of

1) Levator ani • Puborectalis

• Pubococcygeus• Iliococcygeus

2) Coccygeus (Ischiococcygeus)

LEVATOR ANI MUSCLE Contraction of levator ani muscles raises the entire pelvic

floor

Functions:

1) Control of urination & defecationRelaxation 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

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

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

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/oval Pelvic 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, face Ischial tuberosities longer, face

more mediallymore medially

DIFFERENCES BETWEEN MALE & FEMALE PELVIS

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

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

Pelvic Variations

and Abnormalities

PELVIC TYPES BASED ON CALDWELL-MALLOY CLASSIFICATION

Note: Many pelvis are not pure but mixed type. For example – gynaecoid pelvis with android tendency

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

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

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

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

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

Normal Pelvic Variations

Round inlet

Heart-shaped/ triangular inlet

Long oval inlet

Flat inlet

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

FETAL SKULL

FETAL VS ADULT SKULL

TERM FETAL SKULL ADULT SKULL

THE SKULL

Skull is divided into 2 parts:

1) Neurocranium:

Calvaria (skullcap)

Cranial base (basicranium)

2) Viscerocranium (Facial skeleton)

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

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

AdultTerm Fetus

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

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

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

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)

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

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.

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

Intermaxillary sutures

Intermandibular sutures

SUTURES

Frontal suture

Coronal sutureSagittal suture

Lambdoid suture

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

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

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)

4) Trigonocephaly (triangular head)- premature closure of metopic suture

5) Pansynostosis- premature closure of multiple suture

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)

Anterior fontanelle

Posterior fontanelle

Anterolateral (sphenoid) fontanelle

Posterolateral (mastoid) fontanelle

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

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

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

MOLDING OF FETAL SKULL

Molding = adaptation of fetal head to the pelvic cavity during birth

To reduce head circumference

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

THE END

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