2. • Knowledge of the anatomy of a normal pelvis
is needed in midwifery and obstetric practice
• One of the ways to estimate the progress of
labor is by assessing relationship of the fetus
to certain pelvic landmarks.
• Be able to recognize a normal pelvis in order
to detect deviations from normal.
3. Functions:
• Allows movement of the body especially walking and
running
• Allows a person to sit and kneel
• Transmits the weight of the trunk to the legs, acting as a
bridge between the femurs
• Takes the weight of the sitting body onto the ischial
tuberosities
• Contains and protects the bladder, rectum, and the
internal reproductive organs
• The sacrum transmits nerves to various parts of the body
• Provides the skeletal framework of the birth canal
4. Pelvic bones:
• There are 4 pelvic bones:
– 2 innominate bones (nameless) or hip bones
– One sacrum
– One coccyx
5.
6. Innominate bones:
• Each innominate bone is composed of 3 parts:
– The ilium
– The ischium
– The pubic bone
7.
8. The ilium:
– The ilium is the large flared- out part
– When the hand is placed on the hip it rests on the iliac
crest which is the upper border
– At the front of the iliac crest, there is the bony
prominence known as the anterior superior iliac spine
– a short distance below it is the anterior inferior iliac
spine
– On the other end of the iliac crest there are 2 similar
points known as the posterior superior and the
posterior inferior iliac spines
9. The ischium:
• Is the thick lower part
• It has a large prominence known as the ischial
tuberosity on which the body rests when
sitting
• Behind and above the tuberosity is an inward
projection , the ischial spine
• In labour the station of the fetal head is
estimated in relation to the ischial spines
10. The pubic bone:
• Forms the anterior part
• It has a body and two oar-like projections- the
superior ramus and inferior ramus
• The two pubic bones meet at the symphysis
pubis and the 2 inferior rami form the pubic arch
• The space enclosed by the body of the pubic
bone , the rami and the ischium is called the
obturator foramen
11. • On the lower border of the innominate bone
are 2 curves (the greater sciatic notch and
lesser sciatic notch)
• The greater sciatic notch extends from the
posterior inferior iliac spine to ischial spine,
while the lesser sciatic notch lies between the
ischial spine and the ischial tuberosity
12. The sacrum:
• A wedge shaped bone consisting of 5 fused
vertebrae
• The upper border of the 1st sacral vertebra
juts forward and is known as sacral
promontory
• The anterior surface of the sacrum is concave
and is referred to as the hollow of the sacrum
• Laterally the sacrum extends into a wing or
ala
13. • Four pairs of holes or foramina pierce the
sacrum and through these, nerves from
cauda equina emerge to supply the pelvic
organs
• The posterior surface is rough to receive
attachments of muscles
14. Coccyx:
• the coccyx is a vestigial tail
• Consists of 4 fused vertebrae, forming a small
triangular bone
15. Pelvic joints:
• There are 4 pelvic joints:
– One symphysis pubis
– 2 sacroiliac joints
– One sacrococcygeal joint
The symphysis pubis:
• Formed at the junction of the 2 pubic bones
which are united by a pad of cartilage
16. The sacroiliac joints:
• Are the strongest joints in the body
• They join the sacrum to the ilium and thus
connect the spine to the pelvis
The sacrococcygeal joint:
• Formed where the base of the coccyx articulates
with the tip of the sacrum
• Permits the coccyx to be deflected backwards
during the birth of the fetal head.
17. Pelvic ligaments:
• The ligaments connecting the bones of the pelvis
with each other can be divided into 4 groups:
– Interpubic ligaments – between the 2 pubic bones or
at the symphysis pubis
– Sacroiliac ligaments- connects the sacrum and the
ilium
– Sacrococcygeal ligaments- unite the sacrum and the
coccyx
– Sacrotuberous and sacrospinous ligaments- pass
between the sacrum and the ischium
18. • The ligaments of importance in midwifery
practice are the sacrotuberous and
sacrospinous ligaments
• They form the posterior wall of the pelvic
outlet
19.
20. Types of pelvis:
• There are four categories of pelves:
– The gynaecoid pelvis
– The android pelvis
– Anthropoid pelvis
– Platypelloid pelvis
21. Gynaecoid pelvis:
• The best type for childbearing
– Sacral promontory is not prominent
– It has a round brim,
– Generous forepelvis
– Straight side walls
– A shallow cavity
– Well curved sacrum
– Blunt ischial spines
– Sub-pubic arch of 900
22.
23. The android pelvis:
• Resembles the male pelvis
– Heart shaped brim
– Narrow forepelvis
– Side walls converge making it funnel shaped
– Has a deep cavity
– Staight sacrum
– Ischial spines are prominent
– Narrow sciatic notch
– Sub-pubic angle is less than 90o
– Its found in short and heavily built women, who have a
tendency to be hirsute
24. The anthropoid pelvis:
• Has a long oval brim
• The sidewalls diverge
• Sacrum is long and deeply concave
• Ischial spines not prominent
• Sciatic notch and sub-pubic angle are very
wide
– Found in tall women with narrow shoulders
25. Platypelloid pelvis:
• Has kidney shaped brim
• Sacrum is flat
• Shallow cavity
• Ischial spines are blunt
• Sciatic notch and the pubic angle are both
wide
26.
27. The pelvis is divided into false pelvis and true
pelvis.
False pelvis:
• Part of the pelvis situated above the pelvic brim
• Its formed by the upper flared-out portion of the
iliac bones and protects the abdominal organs
• It has no significance in midwifery
28. THE TRUE PELVIS:
• This is the bony canal though which the fetus
must pass through during birth
• It has a brim, a cavity and an outlet
The pelvic brim:
• The brim is round except where the sacral
promontory projects into it
• The midwife needs to be familiar with the fixed
points on the pelvic brim which are referred to as
its landmarks.
29. • These are:
– sacral promontory (1)
– Sacral ala or wing (2)
– Sacroiliac joint (3)
– Iliopectineal line, which is the edge formed at the
inward aspect of the ilium (4)
– Iliopectineal eminence, which is the roughened
area formed where the superior ramus of the
pubic bone meets the ilium (5)
30. – Superior ramus of the pubic bone (6)
– Upper inner border of the body of the pubic bone
(7)
– Upper inner border of the sympysis pubis (8)
31.
32. Diameters of the pelvic brim:
There are 4 main diameters of the brim:
• The anteroposterior or conjugate diameter
• The transverse diameter
• 2 oblique diameters
33. • Anteroposterior or conjugate diameter :–
from the sacral promontory to the symphysis
pubis.
– Is termed as anatomical conjugate if measured to
the upper most point of symphysis pubis. It is
12cm.
– Is termed as obstetrical conjugate when taken to
the posterior border of the upper surface. It is
11cm.
• Obstetrical conjugate represents the available space for
passage of the fetus.
34. – The diagonal conjugate is also measured
anteroposteriorly from the lower border of the
sympysis to the sacral promontory
– It may be estimated vaginally as part of pelvic
assessment and is 12-13 cms.
35.
36. • Transverse diameter -Between the points
furthest apart on the iliopectineal lines –
13cm.
37. Cont.
• The oblique diameter- From one sacroiliac
joint to the iliopectineal eminence on the
opposite side of the pelvic – 12cm.
– There are two oblique diameters and each takes
its name from the sacroilliac joint from which it
arises
– The left oblique diameter arises from the left
sacroilliac joint while the right oblique from the
right sacroiliac joint
38.
39. The cavity:
• Extends from the brim superiorly and the
outlet inferiorly
• The anterior wall is formed by the pubic bones
and sympysis pubis and its depth is 4cm
• While the posterior wall is formed by the
curve of the sacrum which is 12 cm long
• The cavity contains the pelvic colon, rectum,
bladder, and some of the reproductive organs
40. Diameters of the cavity
• Its circular in shape and therefore all the
diameters are considered to be 12 cm.
41. The pelvic outlet:
• Two outlets are described:
– Anatomical outlet
– Obstetrical outlet
• The anatomical outlet is formed by the lower
borders of each of the bones together with
the sacrotuberous ligaments
• The obstetrical outlet is of greater significance
because it includes the narrow pelvic strait
through which the fetus must pass
42. • The narrow strait lies between the sacro-
coccygeal joint, the ischial spines and the
lower border of the sympysis pubis
• Obstetrical outlet is the space between the
narrow pelvic strait and the anatomical outlet
and is diamond in shape
43. Diameters of the pelvic outlet:
• Has 3 diameters:
– Anteroposterior diameter
– Oblique diameter
– The transverse diameter
44. • The anteroposterior diameter extends from
the lower border of the sympysis pubis to the
sacrococcygeal joint and measures 13cm
• The oblique diameter has no fixed points but
is said to be between the obturator foramen
and the sacrospinous ligament and measures
12 cm.
• The transverse diameter extends between the
two ischial spines and is 11 cm.
45.
46. THE PELVIC FLOOR:
• Formed by the soft tissues that fill the outlet of
the pelvis
Functions :
• Supports the weight of the abdominal and pelvic
organs
• Its muscles are responsible for the voluntary
control of micturition and defaecation
• Play an important part in sexual intercourse
47. • During childbirth, it influences the passive
movements of the fetus through the birth
canal and relaxes to allow its exit from the
pelvis
48. Muscle layers:
• The superficial layer is composed of 5
muscles:
– The external anal sphincter encircles the anus
and is attached behind by a few fibres to the
coccyx
– The transverse perineal muscles pass from the
ischial tuberosities to the centre of the perineum
– The bulbocavernosus muscle pass the perineum
forwards around the vagina to the corpora
cavernosa
49. – The ischiocavernosus muscles pass from the
ischial tuberosities along the pubic arch to the
corpora cavernosa
– the membranous sphincter of the urethra is
composed of muscle fibres passing above and
below the urethra- it acts to close the urethra
50.
51. The deep layers is composed three pairs of
muscles which together are known as the
levator ani
• They are so called because they lift or elevate
the anus
• Each levator ani consist of :
– The pubococcygeus muscle which passes from
the pubis to the coccyx
52. – The iliococcygeus muscle passes from the fascia
covering the obturator internus muscle to the
coccyx
– The ischiococcygeus muscle passes from the
ischial spine to the coccyx infront of the
sacrospinous ligament
53.
54. The perineal body:
• A pyramid of muscle and fibrous tissue
situated between the vagina and the rectum
• The apex which is the deepest part is formed
from the fibres of the pubococcygeus muscle
which cross over at this point
• The base is formed from the transverse
perineal muscle
