Obstetric Osteology of the Pelvis Flashcards
What bones make up the pelvis
Made up of 4 bones: 2 innominate bones (bone made up of fusion of ilium, ischium and pubis), the sacrum and the coccyx.
What is the linea terminalis?
Arcuate lines + pectineal line + pubic crest = linea terminalis.
What are the bony landmarks of note in the pelvis?
Points of note: iliac crest, ischial spine (greater and less sciatic notches) and the ischial tuberosity.
Promontory – anterior superior edge of 1st sacral vertebrae.
What features does a gynecoid pelvis have?
Gynecoid pelvis: round inlet, straight side walls (not funnelled), ischial spines not too prominent, well rounded greater sciatic notch, well curved sacrum and sub-pubic arch > 90 degrees.
What’s the difference between a true and false pelvis?
False pelvis – greater pelvis – no obstetric relevance, above the linea terminalis
True pelvis – lesser pelvis – bony canal which is solid and immobile inferior to the linea terminalis
What are the pelvic planes?
Pelvic inlet – entrance into the true pelvis, plane of greatest diameter, plane of least diameter and pelvic outlet – exit of the true pelvis.
How do you clinically assess the pelvic inlet, outlet and mid pelvis?
Pelvic inlet – anteroposterior diameter
Mid Pelvis – check for straight side walls and bispinous diameter (diameter between two spinous processes
Pelvic outlet – infrapubic angle by measuring distance between ischial tuberosities
Describe the pelvic conjugates?
Antero-posterior diameter of the pelvic
• The obstetric conjugate – measured from the sacral promontory to the midpoint of the pubis symphysis
• The diagonal conjugate – measured from the sacral promontory to the inferior border of the pubis symphysis.
What happens to the sacrospinous and sacrotuberous ligaments in childbirth?
Sacrospinous ligament and Sacrotuberous ligament which both relax and stretch during labour under influence of hormones.
