Mechanism of Left Mento-Anterior position:
Attitude: extension of head and back
Position: left (right in case of RMA) mento anterior Presenting part: left/right malar bone
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