Female Pelvis

Introduction:

Female pelvis is known as Gynaecoid is regarded as the true female pelvis because its characteristics give rise to no difficulties in child birth, providing the fetus is of normal size.

Functions:

Allow the movement of the body  

Permits to sit and kneel

Adapted for child bearing         

 Transmits the weight of the trunk to the legs

  Provides protection to the pelvic organs

The sacrum distributes the nerves to the various parts of the pelvis

Pelvic is made up of four pelvis bones:

·         2 innominate bones

·         1sacrum

·         1 coccyx

Innominate bones: composed of three parts:

·         Ilium

·         ischium

·         Pubic bone

The Ilium :

·         Large flared out part

·         Upper border: iliac crest on which hands rest when placed on hip

·         At the front of iliac crest can be felt a bony prominence known as anterior superior iliac spine

·         Short distance below it is anterior inferior iliac spine

·         Similar points at the other end of the iliac crest: posterior superior and posterior inferior iliac spines

·         The concave anterior surface of the ilium is iliac fossa.

The ischium: 

 It is the thick lower part

It has large prominence known as ischial tuberosity on which body rests while sitting.

Behind and little above tuberosity is an inward projection called ischial spine. In labor the station of the fetal head is estimated in relation to the ischial spine.

Pubic bone:

forms the anterior part

 it has a body and 2 oar  projections : superior and inferior ramus

The 2 pubic bones meet at the symphysis pubis

The 2 inferior rami form the pubic arch

 Space enclosed  by the body of pubic bone, the rami and the ischium is called obturator foramen.

The innominate bones contain a deep cup to receive the head of femur called as acetabulum. (all three part of the bone contribute to the acetabulum, ie, 2/5^th of ilium, 2/5^th  of ischium, 1 /5^th of pubic bone)

Lower border of innominate bones : 2 curves are found

  One extends from the posterior inferior iliac spine to the ischial spine, is called greater sciatic notch. It is wide and rounded.

  The other lies between the ischial spine and the ischial tuberosity : lesser sciatic notch

Sacrum:

 Wedge shaped bone consisting of five fused vertebrae

Upper border of the first sacral vertebrae juts forward and is known as sacral promontory  

Anterior surface of the sacrum is concave and is called as hollow of sacrum

Laterally sacrum extends into a wing or ala

4 pairs of holes or foramina pierce the sacrum and the through these nerves from the cauda equina emerge to supply the pelvic organs

  Posterior surface is roughened to receive attachments of muscles

Coccyx:

·         The coccyx is a vestigial tail

·         Consists of 4 fused vertebrae and forms a triangular bone

·         Deflects backward during the process of child birth

Pelvic Joints:-

1 symphysis pubis

2 sacroiliac joints

1 sacro coccygeal joint

Pelvic ligaments:-

Inter-pubic ligaments at the symphysis pubis

Sacroiliac ligaments

Sacro coccygeal ligaments

Sacrotuberous ligament

Sacrospinous ligament

Pelvis

The pelvis is anatomically divided in to a false pelvis and true pelvis.

True pelvis- It is a bony canal through which the fetus must pass during birth. It has a brim, cavity and a outlet.

Falsc pelvis - the false pelvis is formed by the iliac portions of the innominate bones and is limited above by the iliac crests. Its only obstetric function is to support the enlarged uterus during pregnancy. Its boundaries are: posteriorly - lumbar vertebrae, laterally-iliac fossa and anteriorly - anterior abdominal wall.

Brim:

Shape is round

Pelvis tilts forward in the erect posture

Plane of the inlet makes an angle of 55 degree.

High inclination has got obstetrical significances

Sacral angle is more than 90 degree

Axis is downwards and backwards

Landmarks of the pelvic brim:

Sacral promontory 

Sacral ala / wing

 Sacroiliac joint

Ilio pectinal line

Ilio pubic eminence

Pectineal line  

Pubic tubercle

Pubic crest

Symphysis pubis

Cavity: extends from the brim above to the outlet below.

Anterior wall is formed by pubic bones and symphysis pubis and its depth is 4 cms

Posterior wall is formed by the curve of the sacrum and is 12 cms in length

Because of such a difference it forms a curved canal

Shape: It is almost round.

Pelvic outlet: 2 types- anatomical and obstetrical

Anatomical: it is formed by the lower borders of each of the bones together with the sacro tuberous ligament

 Obstetrical outlet: includes the narrow pelvic strait through which thc fetus must pass.