Pelvic Inlet

Boundaries of pelvic Inlet :

Anterior - Horizontal Rami of pubic bones and the symphysis pubis

Posterior - Sacral promontory and the alae of the sacrum

Lateral - Linea terminalis

Diameters - a)Anteroposterior

b) Transverse

c) Oblique

Anteroposterior has three diameters ie

1) Obstetric Conjugate

2) Anatomical Conjugate

3) Diagonal Conjugate

Obstetric Conjugate - It is the distance between the sacral promontory and the nearest point on the posterior surface of the symphysis pubis.

It is shortened in abnormal pelvis

The presenting part of the fetus passes through this at the delivery.

It is difficult to measure clinically and can be calculated indirectly by measuring the diagonal conjugate.

It is 10cm or more.

Diagonal Conjugate - it is the distance from the sacral promontory to the apex of pubic arch.It measures 12cms

Anatomical Conjugate - it is the distance between the sacral promontory and the upper portion of the inner surface of the symphysis pubis and it measures 11cms. It is true Conjugate.

Transverse Diameter- It is at right angles to the Obstetric Conjugate and represents the greatest distance between the lines terminalis on either side. It measures 13.5cms.

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