Posterior Arrest often occurs at around 6 centimeters dilation as the baby's head descends through the pelvis in a posterior position.  The hard back of the head gets caught against the sacrum, forcing the chin to deflex and the forehead to point downward to the cervix.  In this position, the head often rests against the pubic bone, causing cervical edema.  And because the forehead does not apply the proper pressure to the cervix, dilation often stops.

The first thing to try is different positions...squatting, hands-and-knees....by allowing a little extra space in the pelvis, the head might go ahead and rotate.  However, with the chin deflexed, this will be difficult.  If there is no progress in these positions, you might try knee-chest, and this little manipulation.

In the knee-chest position, reach your hand down to see if you can feel the baby's head.  If so, you should be able to feel the anterior fontanelle on the part of your baby's head that is facing toward the front of you body.  NEVER apply pressure to the fontanelles.  However, you can apply pressure just above the fontanelle, on the bony edge.  Now picture in your mind that you are dialing a telephone.  You can do this yourself, or have a helper do it.  You put two fingers just on the bony edge of the anterior fontanelle, and dial to your left.  By this, I mean exert pressure to the left and inward.  This should help flex the head while rotating to a transverse position.  After it has rotated to transverse, and you have flexed the anterior fontanelle until it is almost out of your reach, move your fingers to the posterior fontanelle, which should now be in your reach.  Do the same movement - dialing to the left and inward.  Now, try to hold the head in place while you get up.  I know, this is an awkward movement.  Perhaps someone can help you up.  See if the head stays in place through the next couple of contractions, and descends and/or rotates.  If you continue to see descent of the head, you have been successful.  However, it make take two or three times of repeating this rotation exercise in order for the head to descend enough that it will stay in place.