In a study of occipitoposterior positions of the vertex, one should turn to the three fundamental branches of medicine—anatomy, physiology and pathology—in order to obtain the foundation for the understanding of this complicating obstetric problem.
The anatomy should include the normal female pelvic measurements and the normal measurements of the fetal head. The physiology should give one the mechanism of the engagement of the fetal head in a maternal pelvis, and the pathology the abnormal factors present when the fetal head tries to engage in the posterior position. It should explain how this position differs from the normal engagement of the occiput anterior.
The fetal head presents at the pelvic brim in a military attitude, sitting erect on the shoulders. The diameters opposing each other are the occipitofrontal of from 11 to 11.5 cm. and the suboccipitobregmatic of from 9 to 9.5 cm., while the normal pelvis presents at the
PROCTER IM, DICKINSON K. A STUDY OF THE OCCIPITOPOSTERIOR POSITIONS OF THE VERTEX: ANALYSIS, MANAGEMENT AND RESULTS IN 106 CONSECUTIVE CASES. JAMA. 1940;114(5):381–386. doi:10.1001/jama.1940.02810050001001
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