Pelvic brim Female pelvis MRCOG part 1 - anatomy review for female pelvis

2. • Between the
heads of the
femurs and the
L5
3 BONES: Sacrum
and right and left
hip / innominate,
bones

5. The PELVIC OUTLET is formed by 4 elements of bone:
• the coccyx posteriorly
• pubic symphysis anteriorly
• 2 ischial tuberosities laterally

6. The strong sacrotuberous ligaments stretch between the sacrum/coccyx and the
ischial tuberosities, with the result that the pelvic outlet is described as rhomboid in
shape. The pelvic inlet has a wide, transverse oval opening, whereas the outlet presents
a more oval diameter in its anteroposterior relationship.

7. The shape of the pelvic outlet
: corresponds to 3 wide
arches
1. Subpubic arch anteriorly
2. 2 greater sciatic notches
posteriorly
POSTERIOR REGION OF
ARCHES:
• Each side has
sacrotuberous &
sacrospinous ligaments
(converting the SCIATIC
NOTCHES into
FORAMINA)
FORAMINA, are occupied
by muscles and important
vessels and nerves.

8. These anatomical correlates are
reflected during labour. The fetal
head enters the pelvic inlet positioned
with the longer, anteroposterior
dimension across the widest and,
therefore, transverse diameter of the
pelvis.
At the pelvic outlet, the fetal head is
positioned anteroposteriorly in
relation to the pelvic outlet, this being
the widest diameter of both head and
outlet.
The shape of both the pelvic outlet
and inlet are, therefore, important
considerations in labour, because the
cross-sectional shape of the birth
canal differs at these anatomical
levels.

9. The pubic symphysis, forms a secondary
cartilaginous joint that unites the two pubic
bones via a fibrocartilaginous disc and the
superior and arcuate pubic ligaments.
The latter is separated from the urogenital
diaphragm by an interval, through which the
deep vein of the clitoris enters into the pelvis.

10. The ventral sacroiliac ligament
should not be truly described as a ligament as
it is in fact a thickening of the joint capsule.

11. The dorsal sacroiliac ligament, consisting of quite weak
bands of tissue, arises from the intermediate and lateral
crests of the sacrum which pass down to the posterior
superior iliac spine and the inner lip of the iliac crest.
The lower part of this ligament, arising from the
S3 & S4 segments and passing to the posterior superior
iliac spine, may form a separate structure
termed the long posterior sacroiliac ligament. Some of
the fibres of the posterior sacroiliac ligament, when
present, may also merge with the sacrotuberous
ligament.

13. CLINICAL RELEVANCE
While symphysis pubic dysfunction or pelvic girdle pain is
common in pregnancy, the actual cause of the pelvic
instability is not clear, but probably due to a combination of
change in posture due to increasing abdominal mass and
hormonal through changes in the pelvic ligaments. In
severe cases of pelvic instability there is an associated
increase in symphyseal width.

15. The inguinal ligament is important
surgically in the repair of inguinal
hernia.
The inguinal ligament:
• Is formed by the lower border of the
aponeurosis of the external oblique
muscle folded back upon itself.
• Is fused laterally to the iliacus fascia
and inferiorly to the fascia lata.
• Flattens medially into the lacunar
ligament, which forms the medial
border of the femoral ring.

19. The bony pelvis and its ligaments delineate three important foramina that
allow the passage of the various muscles, nerves, and vessels to the lower
extremity.

20. Lesser Sciatic Foramen
• The lesser sciatic foramen transmits the tendon of
the obturator internus to its insertion on the greater
trochanter of the femur.
• The nerve of the obturator internus and the
pudendal vessels and nerves reenter the pelvis
through the lesser sciatic foramen.

23. • Supporting and compressing abdominal contents!

31. As with the internal oblique muscle, the fibres that take origin from the inguinal ligament
pass downwards and medially over the round ligament and contribute to
the conjoint tendon, which inserts behind the round ligament to the pubic crest and
pectineal line. The rectus abdominis originates from the crest and tubercle of the
pubis and broadens as it ascends to insert on the costal cartilages of the 5th,6th,7th.