LMA/RMA
Mechanism of Left Mento-Anterior position:
Criteria:
Lie: longitudinal
Attitude: extension of head and back
Denominator: mentum
Presentation: face
Position: left (right in case of RMA) mento anterior
Presenting part: left/right malar bone
Principal movements:
Engagement :
The diameter of engagement is the oblique diameter
(right in LMA and left in RMA) with the mentum related to one
ilio pubic eminence and the glabella to the opposite sacro-iliac joint (engaging
diameter is submento bregmatic
Engagement is delayed because of long distance between
the mentum and bi-pårietal plane.
Extension: Descent takes place with increasing extension occurs
till the chin touches the pelvic floor. The mentum becomes the leading part.
Internal rotation of the head occurs when the chin reaches the pelvic
floor and rotates forward 1/ 8th of a circle anteriorly, placing the mentum
behind the symphysis pubis
Further descent occurs till the sub-mentum escapes
under the pubic arch.
Delivery of the head: flexion takes place and the
sinciput, vertex and occiput sweeps the perineum and the head is is born by
movement of flexion.
Restitution occurs when the chin turns 1/8th of circle to the
women's left.
Internal rotation of the shoulders: the shoulders enter the
pelvis in the left oblique diameter and the anterior shoulder reaches the
pelvic floor first and rotates forwards 1/8th of the circle along the right
side of the pelvis.
External rotation of head: occurs simultaneously. The
chin moves further 1/8th of a circle to the left.
Lateral flexion: The anterior shoulder escapes under the symphysis
pubis, the posterior shoulder sweeps the perineum the body is delivered by
movement of lateral flexion
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