pelvis and pelvimetry

1. FEMALE PELVIS
AND
PELVIMETRY
AYMAN SHEHATA
MD Obstetrics and Gynecology
TANTA UNIVRSITY
2015
BY

2. P’S IN LABOR & DELIVERY
1.Passenger= The fetus
2. Passageway= The birth canal
3. Power of labor= Force of uterine contractions

3. Pelvic anatomy
• Bony pelvis
• Pelvic diameters
• Pelvic planes
• Pelvic axes
• Pelvic types
• Pelvimetry

4. The bony pelvis
”four bones“:
• two hip bones(ileum, ischium & pubis) laterally &
anteriorly
• sacrum & coccyx posteriorly
‘3 joints’
• symphysis pubis anteriorly
• sacroiliac joints posteriorly

5. 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

7. 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

8. Hip Bone
In 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.

10. 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.

11. The ischium
 the inferior and posterior part of the hip bone
• ischial spine
• ischial tuberosity

12. 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

14. False pelvis: above the pelvic brim and has no
obstetric importance.
True pelvis: below the pelvic brim and related
to the child -birth.

15. False Pelvis
bordered by:
• lumbar vertebrae posteriorly
• iliac fossa bilaterally
• abdominal wall anteriorly.
supports the abdominal contents
after 1st
trimester helps support the gravid uterus.

16. 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.

18. 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.

20. Pelvic anatomy
• Bony pelvis
• Pelvic diameters
• Pelvic planes
• Pelvic axes
• Pelvic types
• Pelvimetry

21. 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.

23. 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.

24. 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.

25. 4) Anatomical Transverse Diameter (13 cm)
5) Obstetric Transverse Diameter
ATD
OTD

26. 6) Oblique Diameter (12 cm)
7) Sacrotyloid Diameter (9.5 cm)
SI Joint
Iliopubic eminence

27. Pelvic cavity

28. The Cavity..!!!
• Round cavity of greatest dimensions.
• Anteroposterior diameter
• Oblique diameter
• Transverse diameter
12cm

29. 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

31. 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.

32. •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

35. Pelvic anatomy
• Bony pelvis
• Pelvic diameters
• Pelvic planes
• Pelvic axes
• Pelvic types
• Pelvimetry

36. 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

37. 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.

38. Pelvic Inlet
• Plane

39. 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.

41. 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.

43. THOM᾿S DICTUM
IF THE SUM OF TRANSVERSE DIAMETER OF OUTLET AND
POSTERIOR SAGITAL DIAMETER IS LESS THAN 15 CM THE
OULET IS CONTRACTED

45. Pelvic anatomy
• Bony pelvis
• Pelvic diameters
• Pelvic planes
• Pelvic axes
• Pelvic types
• Pelvimetry

46. 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.

47. Pelvic Axes…!!!
• Anatomical Axis of Carus…
Curved axis formed by joining the axis of inlet,
cavity and outlet.

48. Obstetric axis

49. 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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50. 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.
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51. Pelvic anatomy
• Bony pelvis
• Pelvic diameters
• Pelvic planes
• Pelvic axes
• Pelvic types
• Pelvimetry

52. Caldwell- Moloy Classification of
Pelvic Types
• Gynaecoid pelvis(50%)
• Anthropoid pelvis (25%)
• Android pelvis (20%)
• Platypelloid pelvis (5%)
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53. Comparison of pelvic
types

54. Pelvic Types

55. 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

57. • These features create a cylindrical
shape that is spacious throughout.
• The fetal head generally rotates
into the occipitoanterior position
in this type of pelvis.

58. 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

60. • 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.

61. 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

63. • 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.

64. Platypelloid 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.

67. 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.

68. Pelvic anatomy
• Bony pelvis
• Pelvic diameters
• Pelvic planes
• Pelvic axes
• Pelvic types
• Pelvimetry

69. 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)

70. 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

71. 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.

72. 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.

76. 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

79. 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.

82. 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.

85. Pelvic Outlet
1) 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.

88. 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)

89. 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.

91. Adequate Pelvis
Data 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.

92. 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.

93. Indications
1. Clinical evidence or obstetric
history suggestive of pelvic
abnormalities.
2. A history of pelvic trauma.

94. 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)

95. MRl pelvimetry with AP inlet and outlet
measurements.

96. 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.