The pelvis is composed of bones that form a ring and basin shape, including the two innominate bones joined in front by the pubic symphysis and joined behind to the sacrum. The pelvis contains the true and false pelvis, with the true pelvis located below the pelvic brim and containing reproductive organs. Differences exist between male and female pelvises to accommodate childbirth in females, such as a wider and more circular inlet in females. The pelvis has important clinical measurements like the conjugate diameter of the inlet.

1. THE PELVIS
Dr. Towo
29/1/2024

2. OUTLINE
• Introduction
• Ilium, pubis and ischium
• Sacrum and coccyx
• Gender difference
• True and false pelvis
• Pelvic inlet and outlet
• Types of pelvis
• References

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PELVIS
Is a basin-shaped ring of bones that makes the distal
margin of the trunk. It is made up of 2 innominate bones,
one on each side joined anteriorly and articulated with the
sacrum posteriorly.
False Pelvis; The space superior to the pelvic brim.
True Pelvis ;Located below the pelvic brim.

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INNOMINATES BONES
• Composed of 3 parts, Ilium,Ischium and
Pubis.At birth these bones are connected by
cartilage in the area of the acetabulum, Later
between 16&18yrs of age, they fuse into a
single bone.
• ILIUM; Most superior in position.Ilium is
separeted into upper and lower parts by a
rigde in the medial surface.

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• The upper part of the ilium expand to form a
flat,fan shaped wing which provide bony
support for the lower abdomen or false
pelvis.The entire superior margin is thickened
to form prominent crest (the iliac crest) which
terminates anteriorly as the anterior superior
iliac spine & posteriorly as posterior superior
iliac spine.The posterior end of the crest is
thickened to form the Iliac tuberosity.

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HIP BONE/INNOMINATE BONE

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• Applied Anatomy
• Iliac crest lies close to the surface and is easily
palpated hence in certain disease like
Leukemia to assess the stg &severity the Bone
marrow biopsy is taken and the preferably site
is along Iliac Crest.

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PUBIS
• It is anterior and inferior part of the pelvic bone. It has body
& 2arms or Rami.
• The body articulate with the body of the pubic bone on the
other side at the pubic symphysis.On its superior surface
has a cest that end laterally as the prominent Pubic
tubercle.The superior pubic rami has its sharp superior
margins termed as Pecteneal line(Pecten pubis) which form
part of the linea terminalis of the pelvic bone and the pelvic
inlet.The Inferior pubic ramus is marked by the obturator
groove which form upper margin of the obturator Canal.

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ISCHIUM
• Is the posterior & inferior part of the pelvic
bone.Has large body that joins with ilium &
the superior ramus of the pubis superiorly and
a Ramus that projects anteriorlyto join with
the inferior ramus of the pubis.Posterior
margins of the bone is marked by a prominent
Ischial Spine that separates the lesser sciatic
notch below from the greater sciatic notch
above.

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• The most prominent feature of the Ischium is
a large tuberosity (The Ischial Tuberosity)on
the posteroinferior aspect of the bone.This
tuberosity is an important site for the
attachment of lower limb muscle and for
supporting the body when sitting.

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HIP BONE

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SACRUM
• It consist of 5 vertebrae fused together to form a single
wedge-shaped bone with a forward concavity.The upper
border or base of bone articulate with the 5th lumbar
vertebrae.The inferior border articulate with the
Coccyx,laterally it articulate with 2 iliac bones to form
Sacroiliac joints.The anterior & upper margins of the 1st sacral
vertebrae bulge forward as the posterior margin of the pelvic
inlet The Sacral Promontory which is an important obstetric
landmark used when measuring the size of the pelvis.

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COCCYX
• Consist of 4 vertebrae fused together to form
a small triangular bone which articulate at its
base with the lower end of the sacrum.The
coccygeal vertebrae consist of bodies only but
the 1st vertebra posses a rudimentary
transverse process and Cornua projects
upward to articulate with the sacral cornua.

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Gender differences
The pelvis of a female differs from that of male
in several ways many of which has to do with
the passing of a baby during child birth;
• The pelvic inlet in a female is ovoid while it’s
heart-shaped in a male
• Bones are more delicate – thin and light
• The pelvis is less massive

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Cont…
• Wider and more rounded subpubic arch (~90° )
• The ischial spines projects less inward hence not protruding
into the pelvic cavity
• The pelvis is more shallow
• The ilia are less sloped
• The ant. Iliac spines are more widely separated thus the
greater prominence of the hips laterally

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Differences btn female and male pelvis cont…
• The pelvic inlet is larger, more nearly circular
• The cavity of the pelvis is shallower and wider
• Sacrum is shorter, wider and the upper part is
less curved, so the sacral promontory is less
imposing into the pelvic cavity

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Cont…
• Obturator foramina are triangular- oval in
shape and smaller in size than the male
circular foramina
• Pelvic outlet is larger and the coccyx is more
moveable
• The sciatic notches are wider and shallower
• The acetabular are smaller and look more
distinctly forward

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Cont…
• The superior pubic ramus is longer than width
of the acetabulum
• Ischial tuberosities and the acetabulum are
more wide apart
• The pubic symphysis is less deep
• The muscle attachments are poorly marked

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False pelvis
• Is of little clinical importance
• Bounded behind by the L5 S1 vertebrae, posterolaterally by
the iliac fossae and in front by the lower part of the
anterior abd. wall.
• It supports the abdominal contents and after 3rd month of
pregnancy helps supports the gravid uterus, during the
early stages of labor it helps guide the fetus into the true
pelvis

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True Pelvis
• The true pelvis is cylindrical in shape and has inlet and
outlet
• Bounded by the pelvic surfaces of the hip bones, sacrum
and coccyx
• Limited inferiorly by the musculofascial pelvic diaphragm
• It is The location of the pelvic viscera – the urinary bladder,
uterus, ovaries
• It is of major obstetrical and gynaecological significance

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Pelvic inlet
• Is the circular opening between the abdominal cavity and
the pelvic cavity through which structures traverses
between the abdomen and pelvic cavity
• Completely surrounded by bones and joints
• Boundaries-post: ant. Margin of the sacrum and
the sacral promontory
lateral: alae of the sacrum
anterior: pubic symphysis

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Pelvic inlet cont…
• The size and shape of the pelvic inlet is
important because it is through this opening
that the fetal head enters the true pelvis
during labor. The size of the true pelvis is
particularly important in obstetrics because it
is the bony pelvic canal through which the
fetus passes during vaginal birth

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• To determine the capacity of the female pelvis for child
bearing, the diameters of the true pelvis are noted
radiologically or during a pelvic exam
• Has 3 principal diameters:
i) Anteroposterior diameter(also called conjugate) – from the
sacral promontory to the symphysis pubis and measures
11cm

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• Has 2 conjugates
i) True conjugate – measures from sacral
promontory to the top of the symphysis
ii) Diagonal conjugate – measures from sacral
promontory to the bottom of the symphysis

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Diameters cont…
ii) Transverse diameter – extend across the
width from the mid point of the pelvic brim on
one side to the other on opposite side
~13.5cm
iii) Oblique diameter – from the iliopectineal
eminence on one side to the sacroiliac
articulation on the opposite side. Measures
~12.5cm

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Pelvic outlet
• Diamond shaped
• Bounded infront by the pubic and inferior
rami of the pubis and ischia, laterally by the
ischial tuberosities, behind by the
sacrotuberous ligament and the tip of the
coccyx

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Pelvic outlet cont…
• Has 2 diameters
i) Anteroposterior diameter – from the tip of
the coccyx to the lower part of the pubic
symphysis. It measures ~9-11.5cm
ii) Transverse diameter – measured btn the
posterior parts of ischial tuberosities ~11.5
cm

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Types of pelvis
• In 1933, Caldwell and Moloy classified pelvis
into 4 groups
-gynaecoid
-android
-anthropoid
-platypelloid

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Types of pelvis cont..
• Gynaecoid -present in ~41% of women, is the typical
female pelvis, round with enlarged transverse diameter
• Android- present in ~33% of white females and 16% of
black women. It is the male or heart shaped pelvis with a
contracted outlet
• Anthropoid- ~24% of white women and 41% of blacks, is
long, narrow, and oval shaped

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Cont….
• Platypelloid-present in ~ 2% of females, is a
wide pelvis flattened at the brim, with the
promontory of the sacrum pushed forward,
has a long transverse diameter

37. references
• A dissectors guide and atlas - Lord zuckerman
second edition
• Platzer, Werner (2008). Color atlas of human
anatomy
• www.siumed.edu
• en.wikipedia.org/wiki/pelvis
• Entrez PubMed
• Google scholar, various publications