Bony Pelvis Anatomy Flashcards
List the bones that make up the pelvis (4)
- 2 hip bones - one on either side
- sacrum
- coccyx
Which bones fuse together to form the hip bones
- ilium
- ischium
- pubis
Functions of the bony pelvis
Support of the upper body when sitting and standing
Transference of weight from the vertebral column to the femurs to allow standing and walking
Attachment for muscles of locomotion and abdominal wall
Attachment for external genitalia
Protection of pelvic organs, their blood & nerve supplies, their venous and lymphatic drainage
Passage for childbirth
pelvic girdle vs bony pelvis
Coccyx is not part of pelvic girdle
Sacrum is part of pelvic girdle
Other names for hip bone
oscoxa
innominate
Which bones of the hip bone fuse first?
Ischium and pubis at around age 4
What is the significance of acetabulum?
formed by fusion of three hip bones - ‘triradiate”
Bony landmarks of ilium
Iliac crest ASIS AIIS PSIS PIIS
Bony landmarks of ischium
ischio-pubic ramus: where ischium and pubis join together
ischial spine
Ishicial tuberosity - attachment of hamstring
Bony landmarks of pubis
ischio-pubic ramus
superior pubic ramus
pubic tubercle - protrusions in the front
pubic symphysis - joint between the two
pubic arch - forms the sub
pubic angle
What are the boundaries of the pelvic inlet/brim?
- Sacral promontry (sounds like prominent)
- ilium - arcuate line
- superior pubic ramus
- Pubic symphysis
What are the boundaries of the pelvic outlet?
- pubic symphysis
- ischiopubic ramus
- ischial tuberosities
- sacrotuberous ligaments
- coccyx
Features of pelvic cavity
lies within the bony pelvis
continuous with abdominal cavity above
lies between pelvic inlet and pelvic floor
contains pelvic organs and supporting tissues
Significance of pelvic floor
Divides pelvis from perineum
Palpable surface landmarks of the pelvis (anterior)
- Iliac crest
- ASIS
- pubic symphysis - important for fundal height
- pubic tubercle
- inguinal ligamnet: between pubic tubercle and ASIS
palpable surface landmarks of the pelvis (posterior)
- iliac crest
- PSIS
- Sacrum
- Ischial tuberosity
- Coccyx
Joints of the pelvis (location and type)
- hip joint: acetabulum and head of femur - synovial
- Pubic symphysis - secondary cartilaginous
- Sacroiliac joint - synovial anteriorly, syndesmoses posteriorly
Ligaments of the pelvis
Cross joints
Stabilise the joints of the pelvis
- Sacro-tuberous (post) - from sacrum to ischial tuberosity
- Sacro-spinous (ant) - sacrum to ischial spine
Function of pelvic ligaments
- Ensure the inferior part of the sacrum is not pushed superiorly when weight is suddenly transferred vertically through the vertebral column (e.g. when jumping or during late pregnancy)
- The presence of these 2 ligaments also forms 2 foraminae, the greater and lesser sciatic foraminae
Notch vs foramen
Notch is the hole without ligament
Clinical relevance of bony landmarks
- TRAUMA to bony pelvis can result in life threatening haemorrhage and/or damage to pelvic organs
a) common iliac artery and vein
b) sacral plexus in close approximation with bones
c) organs - bladder, rectum, uterus - CHILDBIRTH - pelvis, foetal skull, labour
Male Pelvis vs Female pelvis
- AP and transverse diameter of female pelvis > male pelvis at both inlet and outlet
- Female sub-pubic angle and arch > male
- Depth of female pelvic cavity < male
Foetal skull and childbirth
Fontanelles: anterior and posterior (clinically important)
Moulding: movement of one bone over another to allow the foetal head to pass through the pelvis during labour.
The presence of the sutures and the fontanelles allows the bones to do this
Important terms related to foetal skull
Vertex: between the two parietal eminences & the anterior and posterior fontanelles (diamond) - identification of vertex helps identify fetal position
Occipitofrontal diameter: should be longer than bi-parietal diameter (skull is longer than it is wide) - allows ease of delivery
Describe foetal positioning in relation to pelvic inlet during labour
At pelvic inlet: transverse diameter > AP diameter
In fetal skull: occipitofrontal diameter > biparietal diameter
Therefore, foetus should ideally enter pelvic cavity in the transverse direction (facing either right or left)
Explain the meaning of “station” in childbirth
The distance of the foetal head from the ischial spines .
A negative number - head is superior to the spines
A positive number means the head is inferior to the spines.
Describe foetal positioning in relation to pelvic cavity during labour
While descending through the pelvic cavity, the foetal head should:
- rotate
- be in a flexed position, i.e. chin on chest
Describe foetal positioning in relation to pelvic outlet during labour
At the pelvic outlet, the AP diameter is wider than the transverse diameter
baby should ideally leave the pelvic cavity in an occipitoanterior (OA) position
During delivery the foetal head should be in extension
