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Scientific Basis of Midwifery > Maternal Pelvis > Flashcards

Maternal Pelvis Flashcards

1
Q

What are the 3 main pelvic functions?

A
  1. Enable movement of the body
  2. Walking/running
  3. Sitting/kneeling
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2
Q

What is the pelvic girdle?

A

Basin-shaped cavity consisting of 4 bones:

  • 2 innominate bones
  • 1 sacrum
  • 1 coccyx
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3
Q

What are the 2 innominate bones called?

A

Ilium and Ischium

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4
Q

How long are the walls of the cavity?

A

Anterior wall = 4cm

Posterior wall = 12cm

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5
Q

What is the true pelvis?

A

A bony canal that the foetus must pass through during birth, divided into 3 components:

  1. Pelvic brim
  2. Pelvic cavity
  3. Pelvic outlet
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6
Q

What is the false pelvis?

A
  • Situated above the pelvic brim
  • Formed by the upper flared-out portions of iliac bones
  • Protects abdominal organs
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7
Q

What is the pelvic floor formed of?

A

Tissues which fill the outlet of the pelvis

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8
Q

Describe the ilium

A
  • The upper border is the iliac crest
  • The concave anterior surface is the iliac fossa
  • It is the large flared-out part
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9
Q

Describe the ischium

A
  • It is the thick lower part
  • It has a large prominence known as the ischial tuberosity
  • The pubis forms the anterior part
  • The ischial spines are located here
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10
Q

Describe the sacrum

A
  • Wedge-shaped bone
  • Anterior surface is concave and referred to as the hollow
  • Upper border of 1st vertebrae juts forward and is known as the promontory
  • Consists of 5 fused vertebrae
  • Posterior surface roughened to receive muscle attachments
  • Laterally, bone extends into wing or ala
  • Bone is pierced with 4 pairs of foramina through which nerves emerge to supply pelvic organs
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11
Q

Describe the coccyx

A
  • Consists of 4 fused vertebrae

- It is a vestigial tail

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12
Q

What are the 4 pelvic joints?

A
  1. Symphysis pubis
  2. Sacroiliac joints x 2
  3. Sacrococcygeal joint
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13
Q

Describe the symphysis pubis

A
  • Cartilage between 2 pubic bones

- Unites the rami (ramuses) on the left and right pubic bones

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14
Q

Describe the sacroiliac joints

A
  • Strongest joints in the body

- Join sacrum to ilium and connect the spine to the pelvis

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15
Q

Describe the sacrococcygeal joint

A
  • Formed where the base of the coccyx articulates with the tip of the sacrum
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16
Q

How does relaxin affect pelvic joints?

A
  • Pelvic joints have little mobility in a non-pregnant state

- Relaxin softens joints to make room for foetal head

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17
Q

What is the sacrocotyloid dimension?

A

Passes from the sacral promontory to the iliopectineal eminence on each side and measures 9-9.5cm

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18
Q

What are the 3 diameters of the pelvis?

A
  1. Transverse - extends across greatest width of brim
  2. Oblique - extends from the iliopectineal eminence of 1 side to the sacroiliac articulation of the opposite side
  3. Anteroposterior (Conjugate) - extends from sacral promontory to symphysis pubis
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19
Q

What does the pelvic brim consist of?

A
  • Sacral promontory
  • Wings/ alae of the sacrum
  • R+L sacroiliac joints
  • R+L iliopectineal lines
  • R+L iliopectineal eminences
  • Upper inner border of superior pubic rami
  • Upper inner border of body of pubis
  • Upper inner border of symphysis pubis
20
Q

How is the female pelvis adapted for child bearing?

A
  • Increased width
  • Rounded brim
  • Concave sacrum
  • Shallower than a male pelvis
21
Q

What does a successful labour depend on?

A

The relationship between the size and shape of the maternal pelvis and foetal skull

22
Q

How does the foetus negotiate the pelvis?

A
  • Has to negotiate pelvic cavity by undergoing rotational manoeuvres
  • Sling-like arrangement of pelvic floor muscles encourage rotation of presenting part
23
Q

What are the 4 types of pelvis?

A
  1. Gynaecoid
  2. Android
  3. Anthropoid
  4. Platypelloid
24
Q

What percentage of pelves are gynaecoid?

A

50%

25
Q

What is the angle of the sub-pubic arch in a gynaecoid pelvis?

A

90 degrees

26
Q

Describe the brim and cavity of a gynaecoid pelvis

A
  • Brim is rounded with a generous fore pelvis; encourages round part of foetal head to present
  • Cavity is round with parallel walls and a curved sacrum
27
Q

What is the curve of carus?

A

An imaginary line made up of the axes of the pelvic canal that directs the foetal head upwards, causing lateral flexion during the 2nd stage of labour

28
Q

Give some other physical features of a gynaecoid pelvis

A
  • Shallow cavity and light in weight

- Ischial spines not prominent and blunt

29
Q

Give the dimensions of the gynaecoid pelvis

A

Brim: AP 11cm, oblique 12cm, transverse 13cm
Cavity: AP 12cm, pblique 12cm, transverse 12cm
Outlet: AP 13cm, oblique 12cm, transverse 11cm

30
Q

What percentage of pelves are android?

A

20%

31
Q

Describe the android pelvis

A
  • Triangular/ heart-shaped with narrow forepelvis
  • Prominent ischial spines with convergent side walls
  • Transverse diameter situated at bacl
  • Sacrum is straight
  • Deep cavity
  • Sacro-sciatic notch is narrow
  • Pubic arch = <90 degrees
32
Q

Describe the anthropoid pelvis

A
  • Long oval brim with narrow forepelvis
  • AP diameters longer than transverse
  • Side walls divergent
  • Sacrum long and concave
  • Ischial spines not prominent and blunt
  • Sub-pubic angle = >90 degrees
  • Common in women of African descent
33
Q

What percentage of pelves are anthropoid?

A

25%

34
Q

What percentage of pelves are platypelloid?

A

5%

35
Q

Describe the platypelloid pelvis

A
  • Flat, female-type pelvis
  • Kidney-shaped brim with wide forepelvis
  • Side walls divergent
  • All AP diameters short
  • Transverse diameters long
  • Sacrosciatic notch narrow
  • Sub-pubic angle = >90 degrees
  • Sacrum flat and cavity shallow
  • Ischial spines not prominent and blunt
36
Q

What are the 3 conjugate diameters?

A
  1. True/ Anatomical Conjugate
  2. True/ Obstetric Conjugate
  3. Diagonal Conjugate
37
Q

Describe the anatomical conjugate

A
  • Sacral promontory to upper part of SP

- 12cm

38
Q

Describe the obstetric conjugate

A
  • Upper posterior border of SP to sacral promontory
  • 11cm
  • Represents available space for passage of foetal head through pelvis
39
Q

Describe the diagonal conjugate

A
  • Lower border of SP to sacral promontory
  • 12-13cm
  • Not measured in the UK
40
Q

What is asynclitism?

A
  • Lateral tilting of the head

- Allows biparietal diameter to pass narrowest AP diameter of brim

41
Q

Describe anterior asynclitism

A
  • Anterior parietal bones move down behind the SP until the parietal eminence enters the brim
  • Movement is then reversed and head tilts in opposite direction until posterior parietal bone negotiates sacral promontory and head is engaged
42
Q

Describe posterior asynclitism

A
  • Anterior synclitism in reverse
  • Posterior parietal bone negotiates sacral promontory prior to anterior parietal bone moving behind SP
  • Once pelvic brim has been negotiated, descent progresses normally accompanied by flexion and internal rotation
43
Q

Give a condition of the pelvis that arises from dietary deficiency

A
  • Rachitic Pelvis
  • Pelvis is deformed by rickets in childhood due to malnutrition; weight of upper body presses down on pelvis, causing bow legs and spinal deformity
  • Sacral promontory pushed down and forward and ilium and ischium drawn outwards, resulting in flat pelvic brim
  • Woman usually has CS due to asynclitism
44
Q

Give a condition of the pelvis that arises from developmental anomaly

A
  • Naegele’s Pelvis
  • 1 sacral ala missing
  • Sacrum is fused to the ilium, causing a grossly asymmetric brim
  • Head cannot engage
45
Q

Give a condition of the pelvis that arises from injury and disease

A
  • Trauma
  • Fractured pelvis will develop a callus/ fail to unite
  • Reduce measurement and some degree of contraction
46
Q

What happens to the coccyx during labour?

A

Pushed back

Scientific Basis of Midwifery (22 decks)

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