The female pelvis is made up of four main bones that form a curved canal for childbirth. It has three main divisions: the brim, cavity, and outlet. The brim is oval-shaped, while the cavity is round. The outlet has the largest anteroposterior diameter to allow baby to pass. Key measurements like the true conjugate must be adequate for labor. The sacrum, coccyx, and two innominate bones articulate to provide structure and protection for pelvic organs.

1. THE FEMALE PELVIS
Mukanda. J
(Registered Nurse Midwife)
LWANIKA COLLEGE OF NURSING AND MIDWIFERY

2. Introduction
• The pelvis is a very important structure in
midwifery, because it forms a bony canal through
which a baby passes during the process of birth.
• The outcome of each labour depends on the
passages (the female pelvis and pelvic floor), the
passenger(the foetus), the powers (ability of the
uterine muscles to expel the foetus out of the
uterus through the pelvic canal) and the
individual’s personality.

3. SITUATION
It articulates with the 5th lumbar vertebra above with the
head of the right and left femur in the corrseponding
acetabulum.
SHAPE
It is basin shaped bony structure. It forms a girdle to
provide protection to its internal organs
SIZE
It is the largest formation of the bones in the body.

4. DIAGRAM OF THE PELVIS

5. • It transmits the weight of the trunk to the legs
• It connect the spine to the lower limbs
• It gives protection to the pelvic organs
• It makes attachment for the pelvic muscles
• It gives shape to the individual
• It allows for body movement e.g. Walking, running.
FUNCTIONS

6. • The bone is formed from the cartilage tissue and these keep
on growing as the child grows.
• Complite ossification of the bones take place from 18 – 25
yrs.
• It is composed of the three main parts or 4 main bones
namely:
a) Sacrum
b) Coccyx
c) 2 innominate bones
GROSS STRUCTURE

8. Sacrum
• It roughly a wedge or triangular bone which
forms the posterior part of the pelvis
• It consists of 5 bones/vertebra fused together
• The 5 vertebra have 4 pairs of holes known as
the foramen where they meet or join.
• These holes also facilitate for the passage of the
blood vessels, lympatic s and nerves from the
spine
Gross structure contd.

9. Sacrum contd
• The inner surface of the acrum is smooth and concave
and concavity is known as the hollow of the sacrum
• The outer surface is convex and rough for muscle
attachment.
• The 1st sacral vertebra has widened out pieces on each
side giving an appearance of wings refered to as alae
of the sacrum
Gross structure contd.

10. Sacrum contd.
• At the central part of the upper boarder of the 1st
sacral vertebra there is a protrusion which
protrudes over the hollow of the sacrum known as
the sacral promontory
• There is a canal that opens at the level of the 5th
sacral vertebra allowing for passage of spinal
cord nerve
Gross structure contd.

11. • At the level of the 2nd and 3rd sacral veterbra the
spinal nerves cut in a tail structure known as
caudal equina
• This is the area through which localanaesthesia is
given for the woman not to experience pain
during contration.
Gross structure contd.

12. DIAGRAM OF THE SACRUM

13. Coccxy
• It is the smallest bone on the pelvis
• It trangular in shape and copmrises of 4 fused bones
• Its base lies on the uppermost and articulates with the
sacrum at the sacro-coccygeal joint
• It is mobile and because of that it creates more room for
the fetus to pass through
• It also important for attachment of the pelvic floor
ligaments
Gross structure contd.

14. DIAGRAM OF THE COCCYX

15. Innominate bones
• They are two in number forming the lateral part of
the pelvis
• Each inominate bone is made up of three parts
namely:
- ilium – upper part
- Ischium- lower part
- Os pubis – front part
Gross structure contd.

19. Ilium
• It is the flared out portion which forms the upper 2/5
of the acetabulum
• Like the sacrum the inner part of the ilium is concave
and smooth and its concavity is called the iliac fossa
• The outer surface is rough and makes attachment for
muscles of the buttocks.
• Below the iliac fossa is a line called the ilio-pectineal
line
Gross structure contd.

20. • The upper board of the iliac bone is called the
iliac crest
• Where the iliac crest ends it leaves a promince
called the anterior superior iliac spine
• And below it is the anterior inferior iliac spine and
the distance between the two is 2.5 cm.
Gross structure contd.

21. • Where the iliac crest ends posteriorly is a projection
called posterior superior iliac spine and below it is the
posterior inferior iliac spine
• The posterior inferior iliac spine forms the upper part of
the greater saciatic notch.
• The ilium articulates with the sacrum at the sacro-iliac
joint
• The ilium forms 2/5 of the acetebulum formatiom
Gross structure contd.

22. Ischium
• Is the thick and lowest part of the innominate bone
• Forms 2/5 of the acetebulum
• The thickest part is called the ischio tuberosity ( bones
of the sit)
• About 2.5 cm above and behind of the tuberosity is the
protrusion called the ischial spines
• The ischial spine divides the greater sciatic notch and
lesser sciatic notch
Gross structure contd.

23. Ischium
• There is a small part of the ischium which
ascends to form the pubic arch by fusing with the
descending ramus from the os pubis
Gross structure contd.

25. Pubic bone
• Forms the smallest portion of the innominate bone
• It forms 1/5 of the acetabelum
• It has a body and 2 rami the superior and inferior rami
• The rt and lt pubic bones unit with each other
anteriorly in a square shaped pubic body called
symphysis pubis
Gross structure contd.

26. • The superior ramus extends from the pubic body
towards the ilium and unites at a point know as ilio-
pectineal eminence
• The inferior ramus extend from the ischium towards the
pubic body and unit to form the pubic arch
• The space surrounded by the inferior and superior pubic
ramus and the ischium is known as obturator foramen
which is for the attachment of the pelvic floor muscles
and ligaments
Gross structure contd.

28. There are four main pelvic joints:-
A)2 SACRAL ILIAC JOINT
• Found between 1st and 2nd sacral vertebra and the upper surface
of the ilium.
• They are slightly mobile and are surrounded and suported by the
ligaments
B) SACRAL COCCYGEAL JOINT
• Its between the 5th sacral vertebra and
• The upper border of the coccyx
• It is surrounded by the ligaments and its very mobile
• It allows the coccyx to tilt backwardsduring child birth
Pelvic joints

29. C) Symphysis Pubis
• It’s a pad of cartilage between the two pubic bones
• It measures 4cm long and it has supporting ligaments
• This jointcontains synovial fluid for their movement.
• Active movement may be allowed during pregnancy due
to ation of hormone progesterone which causes the
relaxation of ligaments
• This causes a lot of discomfort and difficulties in walking
Pelvic joint contd.

30. The strong ligament are:-
• Sacral iliac ligament = binds the sacrum and ilium at the
sacro iliac joint and these are the strongest ligament in
the body
• Sacro tuberous ligament =stretch from the lower part of
sacrum to the tuberosity. They pass through the greater
and lesser sciatic notches forming the lateral
boundaries of the pelvic outlet.
Pelvic ligaments

31. • Sacro spinous = they run beneath the sacro
tuberous ligament and extends from the sacrum
and coccyx across the greater sciatic notch to the
ischial spines
• They form the lateral boundary of the cavity as
well as the outlet
Pelvic ligaments contd.

32. Others ligaments involve=
• Interpubic ligaments- surrounds and strengthen
the symphysis pubis
• Orbturator membrane – fills the obturator foramen
• Inguinal ligament/pourparts ligaments- extend
between anterior superior iliac spine and body of
the symphysis pubis
Pelvic ligaments contd.

34. • Its divided into two parts namely;
a. False pelvis
b. True pelvis
The false pelvis
• Lies above the pelvic brim and its bounded by the
iliac fossae laterally, posteriorly lumbar spine and
the abdominal wall anteriorly
• Its of little importance in midwifery
Divisions of the pelvis

35. DIVISION OF THE PELVIS

36. The true pelvis
• Its has obstetrical improtance
• It is composed of the 3 parts:-
a) The brim
b) The cavity
c) The outlet
• The true pelvis form a curved canal through which the
fetus passes to be born
Divisions of the pelvis contd.

37. Divisions of the pelvis contd
The brim/inlet
• Its almost round except where
the sacral promontory
protrudes over the hollow of
the sacrum.
• It has 8 landmarks namely
• Sacro promontory
• 2 sacro iliac joints
• Alae of the sacrum
• The ilio pectineal line rt and lt
• The ilio pectineal eminence rt
and lt
• Upper boarder or top part of
the symphysis pubis
• Boarder of the superior rami
• Part of the pubic bone

39. The cavity
• Lies immediately below the pelvic bri above and the
outlet below
• Its bounded by the following:-
1. The hollow of the sacrum
2. The back of the pubic bone
3. The greater sciatic notch
4. The back of the acetebulum rt and lt
5. The obturator foramen and obturator membranes
6. The posterior part of the symphysis pubis
Divisions of the pelvis contd.

40. Divisions of the pelvis contd.
The outlet
• Its divided into two:-
1. Anatomical outlet
2. Obstetrical outlet
A) Anatomical outlet
Its bounded b y the:-
1. Lower boarder of the
symphysis pubis
2. The inferior rami rt and lt
3. Ischio tuberosity rt and lt
4. The tip of the coccyx

41. B) obstetrical outlet
• Bounded by the:
1. Same lower boarder of the symphysis pubis
2. The iswchial spines
3. The lower boarder of the sacrum
Divisions of the pelvis contd.

42. Divisions of the pelvis contd.
1. Partly as well as the scaro spinous ligaments
• They are useful landmarks for pelvic measurements because
the coccyx tilts backwards and the ligaments are capable of
stretching.
• This creates more room for thr fetus and hence it is refered to
as the obstetrical outlet

43. • They are collectively known as the diameters of the pelvis
A) Dimeters of the brim
1. Antero – posterior diameter :
• Is measured from the centre of the sacro promontory and
the inner upper summit of the symphysis pubis
• It measures 11cm
• It is the smallest diameter of the brim
• It is known as the true conjugate / anatomical conjugate
Dimension/measurements of the
pelvis

44. 2. Oblique diameter:
• Is measured from the sacral iliac joint on one side to the ilio
pectineal eminence on the opposite side.
• It measures 12cm
3. Transverse diameter:
• It measured from one ilio pectineal line to the other
• Its about 13cm
• It’s the longest diameter on the brim
Dimension/measurements the pelvis
contd.

45. 4. Sacro cotyloid diameter:
• Its measured between the sacro promontory to
the ilio pectineal eminence on the same side.
• Its about 9.5cm
B) diameters of the cavity
• Its all round and the diameters are the same.
• They all measure 12cm
Dimension/measurements of the
pelvis contd.

46. C) diameter of the outlet
1) Antero posterior diameter
• Measured from the lower boarder of the symphysis pubis to
the lower boarder of the sacrum at a pointof the sacro
coccygeal joint.
• It measures 13cm
• It’s the longest diameter
• It increases slightly with the movement of the coccyx during
labour
Dimension/measurements of the
pelvis contd.

47. 2. Oblique diameter; 12cm
• Can not be measured accurately because the sacro
tuberous ligament stretch when they are distended by
the fetal head
• It is accepted as lying parallel to the oblique diameter of
the brim and cavity
• 3. Transverse diameter; 11 cm
• Can be measured using 2 areas either between the
ischio spines or ischio tuberosity
Dimension/measurements of the
pelvis contd.

48. Obstetrical conjugated
• Is measured from the centre of the sacro promontory to a point
1.25cm down the posterior surface of the symphysis pubis.
• It measures 10.2cm
Diagonal conjugate
• Is measured from the lower boarder of the symphysis pubis to the
centre of the sacro promontory
• It measures 12 cms
• The diameter gives an index of the pelvic adequancy
• It can be assessed on vaginal examination and it indicates the size
of the pelvic cavity.
Dimension/measurements

49. Dimension/Measurements Contd.

50. • The most important measurements are the
shortest diameters as they indicate whether the
pelvis is adequate for the passage of the fetal
head.
Significancy of the Pelvic diameters

51. • Planes are imaginary flat surfaces drawn at the level of the
brim, cavity and outlet.
• And because the pelvis is a curved canal angles of the
brim, cavity and outlet differ e.g.
• A person standing up right the angle of inclination of the
brim to the floor will be at 60 degrees
• While that of the cavity will be at 30 degrees and that for the
outlet will be at 15 degrees
• Inclination will lessen as the birth canal is distended or
lessen as the fetus descends.
Pelvic inclination/planes of the
pelvis

52. • Planes of the brim: marks the boundary between the
false and the true pelvis
• Plane of the cavity: is the plane of the greatest pelvic
dimensions. The most roomy part of the pelvis. It
passes through the upper boarder of the 3rd sacral
vertebra and the mid point of the symphysis pubis
• The plane of the outlet: is the plane of the least pelvic
dimensions. It passes through lower boarder of the
sacrum and the lower boarder of the symphysis pubis
Pelvic inclination/planes of the pelvis
contd

53. • Its also an imaginary line passing through the
centre of the planes of the brim, cavity and the
outlet
• This line is drawn at right angle to each of this
planes
• It is also known as the curve of calus, that is the
way through which the fetus follows during
delivery
Axis of the pelvis

55. • Maureen A. Hickman, (1985), Midwifery, 2nd Edition. University
Press, Great Britain
• Diane M. Fraser, Margaret A. Cooper,Anna G.W. Nolte, ( 2006),
Myles Textbook for Midwives: African Edition, Elsevier
Churchill Livingstone, China.
• Sylvia Verrals, (1993), Anatomy and Physiology Applied to
Obstetrics, 3rd Edition, Churchill Livingstone, Newyork
REFERENCES