FEMALE PELVISAND

PELVIMETRY

AYMAN SHEHATAMD Obstetrics and Gynecology

TANTA UNIVRSITY

2015

BY

P’S IN LABOR & DELIVERY

1.Passenger= The fetus

2. Passageway= The birth canal

3. Power of labor= Force of uterine contractions

Pelvic anatomy

• Bony pelvis

• Pelvic diameters

• Pelvic planes

• Pelvic axes

• Pelvic types

• Pelvimetry

The bony pelvis”four bones“: • two hip bones(ileum, ischium & pubis) laterally &

anteriorly• sacrum & coccyx posteriorly

‘3 joints’• symphysis pubis anteriorly

• sacroiliac joints posteriorly

Sacrum

• consists of 5 rudimentary vertebrae fused together to form a single wedge-shaped bone with a forward concavity

• The upper border ( base) articulates with the L5• The narrow inferior border articulates with the coccyx. • Laterally, the sacrum articulates with the two iliac bones

• The anterior and upper margins of the first sacral vertebra bulge forward sacral promontory

Coccyx

• consists of 4 vertebrae fused together to form a small triangular bone

• articulates at its base with the lower end of the sacrum • It’s vertebrae consist of bodies only, but the first vertebra

possesses a rudimentary transverse process and cornua. The cornua are the remains of the pedicles and superior articular processes and project upward to articulate with the sacral cornua

Hip BoneIn children:

each hip bone consists of :

• the ilium, which lies superiorly

• the ischium, which lies posteriorly and inferiorly

• the pubis, which lies anteriorly and inferiorly

joined by cartilage at the acetabulum At puberty, >>> fuse together to form one large, irregular bone. articulate with the sacrum at the sacroiliac joints >>>>form the

anterolateral wall of the pelvis articulate with one another anteriorly at the symphysis pubis.

The ilium, the upper flattened part of the hip bone• iliac crest runs between the anterior and posterior superior

iliac spines• Below these spines are the corresponding anterior and

posterior inferior iliac spines

• The iliopectineal line runs downward and forward around the inner surface of the ilium and serves to divide the false from the true pelvis.

The ischium the inferior and posterior part of the hip bone

• ischial spine

• ischial tuberosity

3-The pubis the anterior part of the hip bone • Body bears pubic crest & pubic tubercle and articulates

with the pubic bone of the opposite side at the symphysis pubis

• superior and inferior pubic rami

False pelvis: above the pelvic brim and has no obstetric importance.

True pelvis: below the pelvic brim and related to the child -birth.

False Pelvisbordered by:• lumbar vertebrae posteriorly• iliac fossa bilaterally• abdominal wall anteriorly.

supports the abdominal contents after 1st trimester helps support the gravid uterus.

True Pelvis

bony canal and is formed by:• the sacrum and coccyx posteriorly • the ischium and pubis laterally and anteriorly

It’s internal borders are solid and relatively immobile. The posterior wall is twice the length of the anterior wall. The area of concern to the obstetrician because its

dimensions are sometimes not adequate to permit passage of the fetus.

The Pelvic Inlet (Brim)

Boundaries

Sacral promontory, alae of the sacrum, sacroiliac joints, iliopectineal lines, iliopectineal eminencies, upper border of the superior pubic rami, pubic tubercles, pubic crests and upper border of symphysis pubis.

Pelvic anatomy

• Bony pelvis

• Pelvic diameters

• Pelvic planes

• Pelvic axes

• Pelvic types

• Pelvimetry

Pelvic Inlet

Diameters

(A) Antero -posterior diameters:

Anatomical antero-posterior diameter (true conjugate) = 11cm from the tip of the sacral promontory to the upper border of

the symphysis pubis. Obstetric conjugate = 10.5 cm

from the tip of the sacral promontory to the most bulging point on the back of symphysis pubis which is about 1 cm below its upper border. It is the shortest antero-posterior diameter.

Diagonal conjugate = 12.5 cm i.e. 1.5 cm longer than the true conjugate. From the tip of

sacral promontory to the lower border of symphysis pubis. External conjugate = 20 cm

from the depression below the last lumbar spine to the upper anterior margin of the symphysis pubis measured from outside by the pelvimeter . It has not a true obstetric importance.

Pelvic Inlet

(B) Transverse diameters:

Anatomical transverse diameter =13cm between the farthest two points on the iliopectineal lines. It lies 4 cm anterior to the promontory and 7 cm behind the symphysis. It is the largest diameter in the pelvis.

Obstetric transverse diameter: It bisects the true conjugate and is slightly

shorter than the anatomical transverse diameter.

Pelvic Inlet

(C) Oblique diameters:

Right oblique diameter =12 cm from the right sacroiliac joint to the left iliopectineal eminence.

Left oblique diameter = 12 cm from the left sacroiliac joint to the right iliopectineal eminence.

Sacro-cotyloid diameters = 9-9.5 cm from the promontory of the sacrum to the right and left

iliopectineal eminence, so the right diameter ends at

the right eminence and vice versa.

4) Anatomical Transverse Diameter (13 cm)5) Obstetric Transverse Diameter

ATD

OTD

6) Oblique Diameter (12 cm)7) Sacrotyloid Diameter (9.5 cm)

SI Joint

Iliopubic eminence

Pelvic cavity

The Cavity..!!!

• Round cavity of greatest dimensions.• Anteroposterior diameter• Oblique diameter• Transverse diameter

12 cm

Anatomical outlet

It is lozenge-shaped bounded by;

the lower border of symphysis pubis, pubic arch, ischial tuberosities, sacrotuberous and sacrospinous ligaments and, tip of the coccyx.

The Pelvic Outlet

It is a segment, the boundaries of which are:

Obstetric outlet

• the roof is the plane of least pelvic dimension,• the floor is the anatomical outlet,• anteriorly the lower border of symphysis pubis,• posteriorly the coccyx.• laterally the ischial spines.

•Antero - posterior diameters:

o Anatomical antero-posterior diameter =11cm from the tip of the coccyx to the lower border of symphysis pubis.

o Obstetric antero-posterior diameter = 13 cm from the tip of the sacrum to the lower border of symphysis pubis as the coccyx moves backwards during the second stage of labour.

•Transverse diameters:

o Bituberous diameter = 11 cm between the inner aspects of the ischial tuberosities.

o Bispinous diameter = 10.5 cm between the tips of ischial spines.

Diameters of pelvic outlet

Pelvic anatomy

• Bony pelvis

• Pelvic diameters

• Pelvic planes

• Pelvic axes

• Pelvic types

• Pelvimetry

Pelvic Planes

• imaginary, flat surfaces that extend across the pelvis at different levels.

four planes :

1. The pelvic inlet

2. The plane of greatest diameter

3. The plane of least diameter

4. The pelvic outlet

1-The plane of the inlet:

bordered by:• pubic crest anteriorly• iliopectineal line of the innominate bones laterally• promontory of the sacrum posteriorly.

fetal head enters the pelvis through this plane in the transverse position.

Pelvic Inlet

• Plane

Plane of mid cavity (plane of greatest pelvic dimensions(

pass between the middle of the posterior surface of the symphysis pubis and the junction between 2nd and 3rd sacral vertebrae. Laterally, it passes to the centre of the acetabulum and the upper part of the greater sciatic notch.

It is a round plane with diameter of 12.5 cm.

Internal rotation of the head occurs when the biparietal diameter

occupies this wide pelvic plane while the occiput is on the pelvic floor i.e. at the plane of the least pelvic dimensions.

Plane of obstetric outlet (plane of least pelvic dimensions(:

passes from the lower border of the symphysis pubis anteriorly, to the ischial spines laterally, to the tip of the sacrum posteriorly.

Plane of anatomical outlet:passes with the boundaries of anatomical outlet and consists of 2 triangular planes with one base which is the bituberous diameter.

Anterior sagittal plane: its apex at the lower border of the symphysis pubis. Posterior sagittal plane: its apex at the tip of the coccyx. Anterior sagittal diameter: 6-7 cm

o from the lower border of the symphysis pubis to the centre of the bituberous diameter.

•* Posterior sagittal diameter: 7.5-10 cm ofrom the tip of the sacrum to the centre of the bituberous diameter.

THOM᾿S DICTUM

IF THE SUM OF TRANSVERSE DIAMETER OF OUTLET AND POSTERIOR SAGITAL DIAMETER IS LESS THAN 15 CM THE OULET IS CONTRACTED

Pelvic anatomy

• Bony pelvis

• Pelvic diameters

• Pelvic planes

• Pelvic axes

• Pelvic types

• Pelvimetry

V) Pelvic Axes:

1-Anatomical axis (curve of Carus): It is an imaginary line joining the centre points of the planes of the inlet,

cavity and outlet. It is C shaped with the concavity directed forwards. It has no obstetric importance. 2-Obstetric axis: It is an imaginary line represents the way passed by the head during labour.

It is J shaped passes downwards and backwards along the axis of the inlet till the ischial spines where it passes downwards and forwards along the axis of the pelvic outlet.

Pelvic Axes…!!!

• Anatomical Axis of Carus…

Curved axis formed by joining the axis of inlet, cavity and outlet.

Obstetric axis

N.B. At the Level of Ischial Spines:

1. The plane of obstetric outlet (plane of the least pelvic dimensions) is at this level.

2. The levator ani muscles are situated at this level and its ischio-coccygeous part is attached to the ischial spines.

3. The obstetric axis of the pelvis changes its direction.

4. The head is considered engaged when the vault is felt vaginally at or below this level.

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N.B. At the Level of Ischial Spines:

5. Forceps is applied only when the head at this level (mid forceps) or below it (low and outlet forceps).

6. Pudendal nerve block is carried out at this level.

7. The external os of the cervix is located normally.

8. The vaginal vault is located nearly.9. The ring pessary should be applied above this

level for treatment of prolapse.www.freelivedoctor.com

Pelvic anatomy

• Bony pelvis

• Pelvic diameters

• Pelvic planes

• Pelvic axes

• Pelvic types

• Pelvimetry

Caldwell- Moloy Classification of Pelvic Types

• Gynaecoid pelvis(50%)

• Anthropoid pelvis (25%)

• Android pelvis (20%)

• Platypelloid pelvis (5%)

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Comparison of pelvic types

Pelvic Types

Gynecoid Pelvis• The classic female type.• Found in approximately 50% of women. • Characteristics:

1. Round inlet, with the widest transverse diameter only slightly greater than the AP diameter

2. Side walls straight

3. Ischial spines of average prominence .

4. Well-rounded sacrosciatic notch

5. Well-curved sacrum

6. Spacious subpubic arch, with an angle of approximately 90 degrees

• These features create a cylindrical shape that is spacious throughout.

• The fetal head generally rotates into the occipitoanterior position in this type of pelvis.

Android Pelvis• The typical male type • Found in less than 30% of women• Characteristics:

1. Triangular inlet with a flat posterior segment & the widest transverse diameter closer to the sacrum than in the gynecoid type .

2. Convergent side walls with prominent spines

3. Shallow sacral curve 4. Long and narrow sacrosciatic notch 5. Narrow subpubic arch

• Limited space at the inlet & progressively lessens down the pelvis, owing to the funneling effect of the side walls, sacrum, and pubic rami.

• Restricted space at all levels. • The fetal head is forced to be in the

occipitoposterior position to conform to the narrow anterior pelvis.

• Arrest of descent is common at the midpelvis.

Anthropoid Pelvis

• Resembles anthropoid ape pelvis. • Found in approximately 20% of women• Characteristics:

1. A much larger AP than transverse diameter, creating a long narrow oval at the inlet

2. Side walls that do not converge 3. Ischial spines that are not prominent but

are close, owing to the overall shape 4. Variable, but usually posterior, inclination

of the sacrum 5. Large sacrosciatic notch 6. Narrow, outwardly shaped subpubic arch

• The fetal head can engage only in the AP diameter and usually does so in the occipitoposterior position, because there is more space in the posterior pelvis.

Platypel loid Pelvis

• Flattened gynecoid pelvis.• Found in only 3% of women• Characteristics:

1. A short AP & wide transverse diameter creating an oval-shaped inlet

2. Straight or divergent side walls

3. Posterior inclination of a flat sacrum

4. A wide bispinous diameter

5. A wide subpubic arch

• The fetal head has to engage in the

transverse diameter.

PELVIMETRY• Pelvimetry is the assessment of the

dimensions & capacity of adult female pelvis in relation to the birth of a baby.

• Pelvimetry was heavily used in leading the decision of natural, operative vaginal delivery or CS.

Pelvic anatomy

• Bony pelvis

• Pelvic diameters

• Pelvic planes

• Pelvic axes

• Pelvic types

• Pelvimetry

Types of Pelvimetry

Clinical pelvimetry:

Internal pelvimetry (manually)

pelvic inlet

mid-cavity

pelvic outlet

External pelvimetry（ Pelvimeter） pelvic inlet

pelvic outlet

Imaging pelvimetry:

X-ray

Computerised tomography (CT)

Magnetic resonance imaging (MRI)

Internal Pelvimetry

• Through vaginal examination

• At first prenatal visit screen for obvious contractions.

• In late pregnancy (preferred)– After 37 weeks GA or at the onset of labour– the soft tissues are more distensible– more accurate– less uncomfortable

Pelvic Inlet

1. Palpation of pelvic brim:• The index & middle fingers are moved

along the pelvic brim.

• Note whether round or angulated, causing the fingers to dip into a V-shaped depression behind the symphysis.

2) Diagonal conjugate: • Measured from the lower border of the

pubis to the sacral promontory using the tip of the second finger and the point where the index finger of the other hand meets the pubis

• Normally 12.5 cm & cannot be reached.• If it is felt the pelvis is contracted • True conjugate = diagonal conjugate – 1.5 • Not done if the head is engaged.

The Midpelvis

1) Symphysis: – Height, thickness & curvature

2) Sacrum: – Shape & curvature– Concave usually. – Flat or convex shape may indicate AP constriction

throughout the pelvis. 3) Side walls:

– Straight, convergent or divergent starting from the pelvic brim down to the base of ischial spines.

– Normally almost parallel or divergent

4) Ischial spines prominence:– The ischial spines can be located by

following the sacrospinous ligament to its lateral end.

– Blunt (difficult to identify at all),– Prominent (easily felt but not large) or– Very prominent (large and encroaching on

the mid-plane).

5) Interspinous diameter:– If both spines can be touched

simultaneously, the interspinous diameter is 9.5 cm i.e. inadequate for an average-sized baby.

6) Sacrospinous ligament: – Its length is assessed by placing one

finger on the ischial spine & one finger on the sacrum in the midline.

– The average length is 3 fingerbreadths.

7) Sacrosciatic notch:– If the sacrospinous ligament is 2.5

fingers, the sacrosciatic notch is considered adequate.

– Short ligament suggests forward curvature of the sacrum & narrowed sacrosciatic notch.

Pelvic Outlet1) Subpubic angle:

– Assessed by placing a thumb next to each inferior pubic ramus and then estimating the angle at which they meet.

– Normally, it admits 2 fingers. (90o)

– Angle ≤ 90 degrees suggests contracted transverse diameter in the midplane and outlet.

2) Mobility of the coccyx.– by pressing firmly on it while an

external hand on it can determine its mobility.

3) Anteroposterior diameter of the outlet:– From the tip of the sacrum to the

inferior edge of the symphysis. (>11cm)

4) Bituberous diameter:– Done by first placing a fist between

the ischial tuberosities. – An 8.5 cm distance (4 knuckles) is

considered to indicate an adequate transverse diameter.

Adequate PelvisData Finding

Forepelvis (pelvic brim) Round.

Diagonal conjugate ≥ 11.5 cm.

Symphysis Average thickness, parallel to sacrum.

Sacrum Hollow, average inclination.

Side walls Straight.

Ischial spines Blunt.

Interspinous diameter ≥ 10.0 cm.

Sacrosciatic notch 2.5 -3 finger - breadths.

Subpubic angle 2fingerbreadths (90o).

Bituberous diameter 4 knuckles (> 8.0 cm).

Coccyx Mobile.

Anterposterior diameter of outlet ≥ 11.0 cm.

Radiological Pelvimetry• X-ray:

– Limited value. No role in guiding management.

• CT:– Ease of performance, interpretation, & 10% less

radiation exposure to the fetus .

– Can evaluate fetal lie & position.

• MRI (method of choice): – Lack of ionizing radiation, higher resolution &

contrast but also higher cost.

Indications

1. Clinical evidence or obstetric history suggestive of pelvic abnormalities.

2. A history of pelvic trauma.

CT pelvimetry.

• Breech presentation. A. Anteroposterior view is used to measure the transverse

diameter of the pelvic inlet (≥ 11.5 cm).

B. Lateral view is used to measure the anteroposterior diameter of the inlet (≥10 cm) & midpelvis.

C. Axial view at the level of the fovea of the femoral heads is used to measure the bi-ischial diameter (≥ 9.5 cm)

MRl pelvimetry with AP inlet and outlet measurements.

Cephalometry

• Ultrasonography: is the safe, accurate and easy method and can detect:– The biparietal diameter (BPD).– The occipito-frontal diameter.– The circumference of the head.