THE BONY PELVIS

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THE BONY PELVIS
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THE BONY PELVIS a. Pelvic anatomy b. Pelvic
joints c. Planes diameters of the pelvis d.
Pelvic shapes e. Pelvic size and its clinical
estimation
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a. PELVIC ANATOMY b. PELVIC JOINTS -
Symphysis pubis - Sacroiliac joints -
Relaxation of the pelvic joints (
especially during pregnancy)
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PLANES AND DIAMETER OF THE PELVIS HAVING 4
IMAGINARY PLANES 1. The plane of the pelvic
inlet ( Superior strait ) 2. The plane of the
pelvic outlet ( Inferior strait ) 3. The plane
of the mid pelvis ( least pelvic dimensions ) 4.
The plane of greatest pelvic dimensions (
Has no obstetrical significance ,
it is not considered further)
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HODGE PLANE
I Pelvic inlet II Hodge I through lower
margin of the symphysis III Hodge I through
ischial spine IV Hodge I through the tip of
coccygis
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PELVIC SHAPES CALDWELL - MOLOY CLASSIFICATION
(1933 - 34) Gynecoid pelvis Android
pelvis Anthropoid pelvis Platypelloid
pelvis
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GYNECOID PELVIS - Almost 50 of white women
(Todd Collection study) - Ascertained the
frequency of the four parent pelvic types by
study of Todds Collection ( Caldwell
CoWorkers,1939) ANDROID PELVIS - 1/3 of pure
type pelvis ( white women), 1/6 non white women -
The extreme android pelvis presages poor
prognosis for vaginal delivery - The
frequency of difficult forceps operations
increases
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ANTHROPOID PELVIS - 1/4 pure type pelvis in
white women and nearly 1 1/2 of those in non
white women PLATYPELLOID PELVIS - Rarest of
the pure varieties ( lt 3 ) INTERMEDIATE TYPE
PELVIS - Mixed type - More frequent than pure
types
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CALDWELL MOLOY
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PELVIC SIZE AND ITS CLINICAL ESTIMATION -
Pelvic inlet measurements - Diagonal
conjugate - Engagerment - with engagerment,
the fetal head serves as an internal
pelvimeter to demonstrate that the pelvic
inlet is ample for that fetus.
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PELVIC INLET - Obstetrical conjugate ( normal
gt 10 cm) - Diagonal conjugate CD - 1.5 to 2
cm True conjugate
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PELVIC OUTLET MEASUREMENTS ( diameter between the
ischial tuberosities ) Called as - Biischial
diameter , Inter tuberous diameter, Transverse
diameter of the outlet - The shape of the sub
pubic arch also can be evaluated at the same
time by palpating the pubic rami from the sub
pubic region toward the ischial
tuberosities. - Estimated by placing a
closed fist against the perineum between
the ischial tuberosities, after fist
measuring the width of the closed fist ( usually
gt 8 cm )
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MID PELVIS ESTIMATION - Clinical estimation of
mid pelvis capacity by any direct form of
measurement is not possible -
Suspicion contracted pelvis in this region -
Ischial spines are quite prominent - The side
walls are felt to converge - The concavity of
the sacrum is very shallow - Ischial
diameter of the outlet lt 8 cm
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• Outer measurement
• Distantia spinarum
• Distantia cristarum
• External conjugate (Baudelaque)
• Vaginal examination

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• 95 of all labors is in vertex presentation and
  most commonly ascertained by abdominal palpation
  and confirmed by vaginal examination
• Majority of cases the vertex enters the pelvis
  with the sagittal suture in the transverse pelvic
  diameter
• The fetus enters the pelvis in the Left Occiput
  Transverse Position / LOT (40 of labors) 20
  ROT.
• The head either enters the pelvis with the
  occiput rotated 45o anteriorly from the
  transverse position

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• 20 of all labors the fetus enters the pelvis in
  an Occiput Posterior (OP) position.
• The ROP is slightly more common than LOP and
  posterior positions are more often associated
  with a narrow forepelvis
• The head either enters the pelvis with the
  occiput rotated 45o anteriorly from the
  transverse position

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THE CARDINAL MOVEMENTS OF LABOR ARE

• ENGAGEMENT
• DESCENT
• FLEXION
• INTERNAL ROTATION
• EXTENSION
• EXTERNAL ROTATION
• EXPULSION

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• ENGAGEMENT
• The biparietal diameter, the greatest transverse
  diameter of the fetal head in occiput
  presentations, passes through the pelvic inlet is
  designated engagement (during the last few weeks
  of pregnancy)
• A normal sized head usually does not engage
  with its sagittal suture directed
  anteroposteriorly.
• Instead, the fetal head usually enters the
  pelvic inlet either in the transverse diameter or
  in one of the oblique diameters.

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• ASYNCLITISM
• Although the fetal heads tends to accommodate to
  the transverse axis of the pelvic inlet, the
  sagittal suture , while remaining parallel to
  that axis, may not lie exactly midway between the
  symphysis and sacral promontory
• The sagittal suture frequently is deflected
  either posteriorly toward the promontory or
  anteriorly toward the symphysis.
• Such lateral deflection of the head to a more
  anterior or posterior position in the pelvis is
  called asynclitism
• Moderate degrees of asynclitism are the rule in
  normal labor, but if severe , may lead to CPD

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• DESCENT
• In nulliparas, engagement may take place before
  the onset of labor and further descent may not
  follow until the onset of second stage. In
  multiparous women, descent usually begins with
  engagement.
• Descent is brought about by one or more of four
  forces
• Pressure of the amniotic fluid
• Direct pressure of the fundus upon the breech
  with
• contractions
• Bearing down efforts with the abdominal muscles
• Extensions and straightening of the fetal body

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