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Scientific Basis of Midwifery > Maternal Pelvis > Flashcards

Flashcards in Maternal Pelvis Deck (46)
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What are the 3 main pelvic functions?

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


What is the pelvic girdle?

Basin-shaped cavity consisting of 4 bones:
- 2 innominate bones
- 1 sacrum
- 1 coccyx


What are the 2 innominate bones called?

Ilium and Ischium


How long are the walls of the cavity?

Anterior wall = 4cm
Posterior wall = 12cm


What is the true pelvis?

A bony canal that the foetus must pass through during birth, divided into 3 components:
1. Pelvic brim
2. Pelvic cavity
3. Pelvic outlet


What is the false pelvis?

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


What is the pelvic floor formed of?

Tissues which fill the outlet of the pelvis


Describe the ilium

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


Describe the ischium

- 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


Describe the sacrum

- 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


Describe the coccyx

- Consists of 4 fused vertebrae
- It is a vestigial tail


What are the 4 pelvic joints?

1. Symphysis pubis
2. Sacroiliac joints x 2
3. Sacrococcygeal joint


Describe the symphysis pubis

- Cartilage between 2 pubic bones
- Unites the rami (ramuses) on the left and right pubic bones


Describe the sacroiliac joints

- Strongest joints in the body
- Join sacrum to ilium and connect the spine to the pelvis


Describe the sacrococcygeal joint

- Formed where the base of the coccyx articulates with the tip of the sacrum


How does relaxin affect pelvic joints?

- Pelvic joints have little mobility in a non-pregnant state
- Relaxin softens joints to make room for foetal head


What is the sacrocotyloid dimension?

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


What are the 3 diameters of the pelvis?

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


What does the pelvic brim consist of?

- 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


How is the female pelvis adapted for child bearing?

- Increased width
- Rounded brim
- Concave sacrum
- Shallower than a male pelvis


What does a successful labour depend on?

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


How does the foetus negotiate the pelvis?

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


What are the 4 types of pelvis?

1. Gynaecoid
2. Android
3. Anthropoid
4. Platypelloid


What percentage of pelves are gynaecoid?



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

90 degrees


Describe the brim and cavity of a gynaecoid pelvis

- 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


What is the curve of carus?

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


Give some other physical features of a gynaecoid pelvis

- Shallow cavity and light in weight
- Ischial spines not prominent and blunt


Give the dimensions of the gynaecoid pelvis

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


What percentage of pelves are android?