LSA/RSA:
Mechanism of left sacro anterior:
Lie: longitudinal
Attitude: complete flexion/ compaction
Denominator: sacrum
Presentation: breech
Position: left/right sacro anterior
Presenting part: anterior (left/right) buttock
Buttocks :
The diameter of engagement of the buttocks is one of
the oblique diameter of the inlet. The engaging diameter is bi-trochanteric
(10cm) with sacrum directed towards the ilio-pubic eminence. When the diameter
passes through the pelvic brim, breech is engaged
Compaction: Descent takes place with increased compaction, due
to increased flexion of the limbs.
Internal rotation of buttocks: The anterior buttock
reaches the pelvic floor first and rotates forwards 1/8th of a circle along the
right side of the pelvis to lie underneath the symphysis pubis. The bi-trochanteric
diameter is now in the anteroposterior diameter of the outlet.
Lateral flexion of the body: the anterior buttock escapes
under the symphysis pubis, the posterior buttocks sweeps the perineum and the
buttocks are born by movement of lateral flexion.
Delivery of the trunk and the lower limbs follow.
Restitution of the buttocks: The anterior buttock turns
slightly to the mother's right side.
Internal rotation of the Shoulders : the shoulders enters the
pelvis in the same oblique diameters as the buttocks, the left oblique. The
exterior shoulder rotates forwards 1/8 th of the circle along the right side of
the pelvis and escapes under the symphysis pubis, the posterior shoulder sweeps
the perineum and the shoulders are born.
Internal rotation of the head: the head enters the pelvis
with the sagital suture in the transverse diameter of the brim. The occiput
rotates forwards along the left side and the sub occipital region (the nape of
the neck) impinges on the under surface of the symphysis pubis.
External rotation of the body: at the same time the body
turns so that the back is uppermost.
Birth of the head: The chin, face, sinciput sweeps the perineum and the
head is born in a flexed attitude.
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