Pelvis definition, pelvis parts, pelvis functions, pelvis structure, pelvis ligaments, pelvic floor, pelvic joints, effect on labour, pelvic inclination, possible injuries in birth canal during labour, ways of preventing injuries in birth canal during labour.

2. PREPARED BY
Prija Pokhrel
Pelvis

3. THE PELVIS/BONY GRIDLE/PELVIC GRIDLE
• A bony griddle formed anteriorly and laterally by the innominate
bone and posteriorly by the sacrum and coccyx is known as pelvis.
• The bony pelvis is a basin like structure.
• It has a muscular floor and contains the uterus, fallopian tubes,
ovaries and urinary bladder.
• The ligaments join the bones of the pelvis and help to keep the
pelvic and abdominal organs in place and join the trunk to the
lower limbs.
• In female, it is adopted for child bearing.

5. PARTS OF PELVIS
• Two innominate bone or hip bone
• One sacrum bone
• One coccyx bone

6. Innominate bone
• It is also known as hip bone
or nameless bone, the two
innominate bones form the
three sides of the pelvis.
Each innominate bone
consists of three parts;
• 1. the ilium
• 2. ischium
• 3. pubis

7. The ilium

8. The ilium...
• It is the large flared out part.
• When the hand is placed on the hip it rests on the iliac crest,
which is the upper boarder.
• It has two surfaces;
 the inner surface is concave and is called Iliac fossa.
 The upper outer surface is convex and is called the iliac crest.

9. The ilium...
• The ilium has two projections;
 the projection in front is called the anterior superior iliac spine.
 the ones at the back are called the posterior superior iliac spine.
• The two posterior superior iliac spines are marked by two dimples,
below each anterior and posterior superior iliac spine lie the inferior
iliac spines.

10. Ischium

11. Ischium…
• It is the thick lower part.
• The thick rounded and thickest part of the ischium is known as the
ischial tuberosity.
• This is the part on which the body rests while sitting.
• The sharp projection above the ischial tuberosity which is directed
backwards and slightly inwards are known as the ischial spines.
• These are the inner aspects of ischium and are important when doing
vaginal examination

12. Pubis

13. Pubis…
• It is also known as pubic bone.
• It forms the anterior part.
• It has the body and two ear like projections; the superior ramus and
the inferior ramus.
• The superior ramus and the ischium join and form the ilio-pectineal
eminence.

14. Pubis…
• The public arch lies below the symphysis pubis.
• The inferior ramus of pubis and inferior ramus of ischium forms
obturator foramen.
• The innominate bone contains a deep cup to receive the head of the
femur.
• This is termed as the acetabulum.
• The two pubic bones are connected by the cartilage in front and is
called symphysis pubis.

15. Sacrum
• The sacrum is located behind the
pelvic.
• Five bones fused into triangular
shape and form a sacrum.
• The sacrum fits between the
two hip bones connecting the
spine to the pelvic.
• The last lumber vertebrae
articular with sacrum.

16. Coccyx
• It can be move backward and
forwards.
• Though the movement is very little, it
helps in the process of normal birth of
a baby by increasing the diameter of
the pelvic outlet.
• This consists of the fourth terminal
vertebrae fused to form a very small
triangular bone called coccyx and
articulates with the tip of the sacrum.

17. FUNCTIONS OF PELVIS
1. The pelvic helps the body to maintain its balance to support our body
weight.
2. The pelvis is a basin like structure which helps to protect the
reproductive organs(uterus, ovaries, fallopian tubes), urinary bladder
and the other organs contained in the pelvis.
3. It helps in locomotion and in the movement of the body.
4. It permits sitting and kneeling.

18. FUNCTIONS OF PELVIS…
4. The pelvic form the part of the birth canal since uterus lies inside the
pelvic and fetus must come through this bony canal so it give birth
canal.
5. The sacrum contains foramina which provide a passage to transmit
nerve from cauda equine to pelvic organs.
NOTE: The collection of nerves at the end of the spinal cord is known as
cauda equine.

19. PELVIC JOINTS
• There are four pelvic joints;
 one symphysis pubis
 two sacro – iliac joints
 one sacro-coccygeal joints

20. PELVIC JOINT…
1. One symphysis pubis:
• It is formed at the junction of the two pubic bones which are
united by a pad of cartilage.
• 2. Two sacro – iliac joints:
• These are the strongest joint in the body.
• They join the sacrum to the ilium and thus connect the spine to
the pelvis.

21. PELVIC JOINT…
• 3. One sacro-coccygeal joint:
• This is the joint between sacrum and coccyx.
• This joint is important in midwifery because it can increase
the diameter of the pelvic outlet.
• This joint allows permits coccyx to be deflected backwards
during the birth of the head.

22. PELVIC LIGAMENTS
• Each of the pelvic joint
is held together by
ligaments. They are
made of fibrous tissue.
They are :
a. Sacro tuberous
ligaments: It is attached
to the posterior aspect
of the lower 3 sacral
vertebrae and medial
border of ischial
tuberosity.

23. PELVIC LIGAMENTS…
b. Sacro spinous ligaments: It is triangular and thin .It extends from the
lateral border of the sacrum and coccyx to the ischial spines.
c. Sacro iliac ligament: It pass in front of and behind each sacroiliac joint.
d. Pubic ligament: It connect the top of pubic bones.
e. Sacro coccygeal ligament: One ligament on each side from sacrum to
coccyx.

24. STRUCTURE OF PELVIS
1.The false pelvis:
• It is the part of the pelvic lying
above the pelvic brim.
• Its only obstetric function is to
support the gravid uterus.
• It consists posteriorly
the lumber vertebrae, laterally the
iliac fossa and anteriorly the
anterior abdominal wall.

25. STRUCTURE OF PELVIS…
• 2. The true pelvis:
• It is the part of the pelvic lying below the pelvic brim.
• It is bony passage through which the baby must pass during labour in
vaginal delivery.
• It is shallow in front formed by symphysis pubis and measures 4cm,
and deep posteriorly, formed by the sacrum and coccyx and measures
11.5cm.
• For descriptive purposes, true pelvis is divided into:
1. The pelvic inlet (brim)​
2. pelvic cavity​
3. pelvic outlets.

26. The pelvic inlet
• The brim is round except where the sacral promontory projects into it.
• The promontory and wings of the sacrum form its posterior border,
the iliac bones its lateral border and the pubic bone its anterior border.
• The midwife needs to be familiar with the fixed points on the pelvic
brim which are known as its landmarks.

27. The pelvic inlet...
• The landmarks of pelvic brim
are:
1. Sacral promontory
2. Sacral ala or wing
3. Sacroiliac joint
4. Ilio- pectineal line
5. Ilio- pectineal eminence

28. The pelvic inlet...
6. Superior ramus of the pubic bone ( Ramus of pubic ).
7. Upper inner border of the body of the pubic bone ( summit of
symphysis pubis ).
8. Upper inner border of the symphysis pubis.
• Shape: It is almost round with the antero- posterior diameter being the
shortest.
• Plane: It is an imaginary flat surface bounded by the bony points.

29. The pelvic inlet...
• Diameters of pelvic brim:
•
• The main pelvic diameters of
the pelvic brim(inlet) are
as follows:-
• 1. Antero-posterior diameter
 anatomical conjugate
 obstetric conjugate
 diagonal conjugate
• 2. Oblique diameter
• 3. Transverse diameter

30. The pelvic inlet...
1. Antero- posterior diameter:
 True conjugate, anatomical conjugate :
• It is the distance between the midpoints of the sacral promontory to the
inner margin of the upper border of symphysis pubis which measures
11cm and isn’t shortest diameter in A.P. palne.
• In actual practice, the it can't be estimated directly .
• However , its measurement is inferred by subtracting 1-2 cm from
the diagonal conjugate.

32. The pelvic inlet...
 Obstetric conjugate:
• It is the distance between the midpoints of the sacral promontory
to prominent bony projection in the midline on the inner surface of
the symphysis pubis.
• It measures 10cm and is shortest antero-posterior diameter
in the antero-posterior plan of the inlet.

33. The pelvic inlet...
 Diagonal conjugate:
• It is the distance between the lower borders of the symphysis pubis to
the midpoint of the sacral promontory .
• It measures 12 cm .
• The diameter is measured through vaginal examination

34. The pelvic inlet...
2. Oblique diameter:
• ​It is line form one sacroiliac joint to the ilio-pectinal eminence on the
opposite side of the pelvis and measures 12cm .
• There are two oblique diameters as left and right.
• The right oblique begins at the right sacroiliac joint and the left oblique
from the left sacroiliac joint.

35. The pelvic inlet...
3. Transverse diameters:
• It lies between the farthest two points on the ilio-pectineal 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 bisects the true conjugate and is slightly
shorter than the anatomical transverse diameter.
NOTE: Sacro-cotyloid diameter- Distance between the mid points of the
sacral promontory to iliopectineal eminence and measures 9.5cm.

36. The pelvic cavity…
• It is almost circular or round shape.
• Cavity is the segment of the pelvis bounded above by the inlet
and below by plane of least pelvic dimensions.
NOTE: Plane of least pelvic dimensions- The plane that extends
from the end of the sacrum to the lower border of the pubic
symphysis, bounded posteriorly by the end of the sacrum,
laterally by the ischial spines, and anteriorly by the lower
border of the pubic symphysis.

37. The pelvic cavity…
• The anterior wall is formed by the pubic bones and symphysis pubis and
its depth is 4cm.
• The posterior wall is formed by the curve of the sacrum which is 12cm
in length. because there is such a difference in these measurements, the
cavity forms a curved canal.

38. The pelvic cavity…
• It’s lateral walls are the sides of the pelvis which are mainly covered by
the obturator internus muscle.
• Shape: It is almost circular or round shape
• Plane: The plane extends from the mid point of posterior surface of
symphysis pubis to the junction of second and third sacral vertebrae.

39. The pelvic cavity…
• Landmarks:
 Hollow of the sacrum.
 Sacroiliac joints.
 Ischial and sacrospinous ligaments.
 Right and left upper and lower pubic rami.
 Bodies of the pubis and symphysis pubis.

40. The pelvic cavity…
Diameters of the pelvic cavity:
• Anterior –posterior ,oblique and transverse diameter is same e.g.
approximately 12cm because of round cavity.

41. Mid cavity
• An important feature of the pelvic cavity is that the ischial
spine project slightly into it.
• These can be felt easily during vaginal examination, this is
an important landmark.
• The level of the ischial spines is the mid cavity; the above the ischial
spines is known as high cavity and below the ischial spine is low cavity.

42. Mid cavity…
• The ischial interspinous diameter is 10 to 10.5cm and is the
smallest diameter of the pelvis.
• If the ischial interspinous diameter is narrow, it causes
pelvic dystocia i.e. prolonged labour.

43. The Pelvic Outlet
• It is diamond shape and
bounded anteriorly
by the sub pubic arch,
laterally by the
ischial tuberosities and
the sacro-
tuberous ligament and
posteriorly by the tip of the
sacrum.

44. The Pelvic Outlet…
• Shape: It is antero- posteriorly oval.
• Plane: The plane is otherwise known as plane of least pelvic dimensions
or narrow pelvic plane. The plane extends from the lower border of the
symphysis pubis to the tip of ischial spines and posteriorly to meet the
tip of the 5th sacral vertebrae.

45. The Pelvic Outlet…
Diameter of pelvic outlet
• The antero-posterior diameter:
 It extends from the lower border of the symphysis pubis to the sacro-
coccygeal junction.
 It measures13cm.
 As the coccyx may be deflected backwards during labour this diameter
indicates the space available during delivery.

46. The Pelvic Outlet...
• The oblique diameter:
 It is said to be between the obturator foramen and the sacro spinous
ligament, although there is no fixed points.
 The measurement is taken as being 12cm.
• The transverse diameter
 It is the distance between the inner surface of the ischial tuberosites
(two).
 It measures10-11cm and is the narrowest diameter in pelvis.

47. The Pelvic Outlet...
• The posterior sagittal diameter:
 It is the distance between the mid of the transverse diameter of the
outlet up to the sacrococcygeal joint and is 9cm

48. AP diameter Oblique diameter Transverse
diameter
Pelvic inlet 11 12 13
Pelvic
cavity
12 12 12
Pelvic
Outlet
13 12 11
STRUCTURE OF PELVIS…

49. TYPES OF PELVIS

50. TYPES OF PELVIS…
• There are many types of pelvis but in midwifery we are
concerned with the four most common types found in
women. They are classified as:
• the Gynaecoid pelvis
• the anthropoid pelvis
• the android pelvis
• the platypelloid pelvis

51. TYPES OF PELVIS…
The gynaecoid pelvis:
• This is the most common type of pelvis in women.
• It is known as the true female pelvis.
• Its cavity is shallow and spacious which allows for easy delivery.
• More than 50 percentage women have this type of pelvis.
• The sacrum in this pelvis is well curved, the sub pubic arch is 90 degree
and more and the sacrosciatic notch is wider compared to other pelvis.
• The iliac crest is broad and well curved

52. TYPES OF PELVIS...
The anthropoid pelvis:
• This type of pelvis is narrow and deep.
• It is oval in shape.
• Women with this type of pelvis tend to be tall with narrow shoulders.
• Found in 15% in Asian women; 15 to 30% on white women.

53. TYPES OF PELVIS...
The android pelvis:
• It is male type pelvis.
• This type of pelvis is likely to occur in tall women with narrow hips and
is also found in African women.
• It is funnel shape with a deep cavity and a straight sacrum.
• Found in 0.6% in Asian women ; 2-8% on white women.

54. TYPES OF PELVIS…
The platypelloid pelvis:
• It is also called a flat pelvis and shortened with a flattened transverse
,oval shape.

55. THE PELVIC FLOOR
 The pelvic floor
is a muscular
diaphragm that
separates the
pelvic cavity
above from the
perineal space
below.

56. THE PELVIC FLOOR…
 Functions of pelvic floor:
• It support the weight of the abdominal and pelvic organs.
• To maintain the continence of urine and feces.
• Allows voiding, defecation, sexual activity and childbirth

57. THE PELVIC FLOOR…
Muscle of pelvic floor:
• Pelvic floor is made up of a number of muscles, which are further
organized as:
• Superficial muscle layer
• Deep muscle layer

58. THE PELVIC FLOOR…
• Superficial muscle layer:
• It includes five muscles;
 The external anal sphincture encircles the anus and is attached behind
by a few fibres to the coccyx.
 Transverse perineal muscle pass from the ischial tuberocity to the centre
of the perineum.

59. THE PELVIC FLOOR…
 Bulvocavernous also called Bulvospongiosus muscle pass from the
perineum forwards around the vagina to the corposa cavernosa (Erectile
body part of clitoris) of the clictoris
 The ischiocavernous muscles pass from the ischial tuberosity along the
pubic arch to the corposa cavernosa.
 The membranous sphincter of the urethra is composed of muscle fibre
passing above and below the urethra and attached to the pubic bones.

60. THE PELVIC FLOOR…
Deep muscle layer:
• Deep muscle layer is composed
of three pairs of muscles which
together are known as levator
ani muscle.
• They are so called because they
lift or elevate the anus.
• Each levator ani muscle ( left
and right) consists of the
following;

61. THE PELVIC FLOOR…
the pubococcygeus muscle:
• Pubococcygeus muscle passess from the pubis to the coccyx
with a few fibres crossing over in the perineal body to form its
deepest part.
the iliococcygeus muscle:
• The iliococcygeus muscles pass from the fascia covering the
obturator internus muscle( the white line of pelvic fascia) to
the coccyx.

62. THE PELVIC FLOOR…
 Ischiococcygeous muscle:
• Ischiococcygeous muscle passes from the ischial spine to
the coccyx in front of the sacrospinous ligaments.

63. PELVIC INCLINATION
• When a women stands up in an upright position, the pelvic
brim is not horizontal but is tilted at an angle of 60 degrees,
this angle is called inclination of the pelvis.
• The angle of brim is 60 degree, the cavity is 30 degree and the
outlet is 15 degree.
• The pelvic inclination is important in the mechanism of labor.

64. EFFECT ON LABOUR
Gynaecoid:
 Fetal head:
• Engage in transverse or oblique diameter, slight asynclitism, good
flexion.
 Labour:
• Good pains, and average fetal size, internal rotation and delivery.
 Prognosis:
• Good

65. EFFECT ON LABOUR…
Android:
 Fetal head:
• Engages in transverse or posterior diameter marked asynclitism,
marked moulding.
 Labour:
• Deep transverse arrrest is common. Instrumental delivery often
needed. Deep perineal tears can occur.
 Prognosis:
• Guarded

66. EFFECT ON LABOUR…
Anthropoid:
 Fetal head:
• Engages in antero-posterior diameter, often occiput presentation or
oblique.
 Labour:
• Delivery is usually easy, face to pubis delivery is common.
 Prognosis:
• Good

67. EFFECT ON LABOUR…
Platypelloid:
 Fetal head:
• Engages in transverse diameter with marked asynclitism
 Labour:
• Delay at inlet, thereafter easy birth.
 Prognosis:
• Guarded

68. Possible injuries of the birth canal during labour
• Mild abrasion and lacerations of the cervix, vagina, vulva and the
perineum occur in labour. The following injuries may occur during
labour
i. Laceration of the vagina
ii. Perineal laceration and tear
iii. Labial laceration
iv. Cervical laceration and tear.
v. Uterine rupture.

69. Ways of preventing injuries to the birth canal
1.Educate mother about breathing exercise during labour i.e. when
to pant and push. The mother should not push early (before the
cervix is fully dilated). The mother should be encouraged and asked
to push and pant at the proper time. She should particularly be asked
to pant when the head is crowning and this should happen at the
end of contraction.

70. Ways of preventing injuries to the birth canal…
2. Explain her why she should not push too soon and also the importance
of deep breathing and panting
3. Control of the fetal head during the second stage of labour is very
important to prevent excessive tear of the perineum.
4. Head should be delivered by slow extension.

71. Reference
• Tuitui, R.( 2016). Manual of Midwifery-I. 11thedition. Vidyarthi Pustak
Bhandar
• Prasai D.S, Bhattarai S.G. (2016) Midwifery Nursing. 3rd edition.
Medhavi Publication.
• Dutta, D.C.(2018) Textbook of Obstetrics. 9thedition. Jaypee brother’s
medical publishers (P) Ltd.
• Retrived from Jill Seladi, S. Female pelvis overview. Updated on July 13,
2018. Healthline. https://www.healthline.com/human-body-
maps/female-pelvis. Retrived on 2078/2/25

72. THANK YOU 