Book of Medical Disorders in Pregnancy - Tintash

The Procedure:
The patient stands in a symmetric profile
position with her side against the vertical
Bucky diaphragm of the X-Ray machine.
The X-Ray tube is centered just above
the femoral trochanters. The tube-film
distance is kept at 36 inches. A metallic
perforated ruler is placed close to the
sacrum or symphysis pubis in the
midsagittal plane of the patient. It is kept
parallel to the film. An experienced rad
biographer keeps the thickness of the
patient in mind while exposing his
patient to the amount of radiation
necessary for a good quality X-Ray film.
The lateral isometric film provi-des qu
ite accurate measurement of the obstetric
conjugate and helps to rule out the inlet
contraction. Such a film can be obtained
by a standard X-Ray machine, the only
special equipment needed is a metal
ruler with centimeter notches or
imperforations. A review of the contours
and bony anatomy of the lateral view of
the pelvis will facilitate location of the
symphysis, sacrum, and ischial spines.
This can be easily accomplished with a
little practice.
Technique of measurement
The Lateral Film:
Any diameter can be measured by
measuring the area between two end
points which are visible on the X-Ray
film. The image of the centimeter scale
on the film provides useful guide to
correct magnification factor. Diameters
that can be reliably measured are the
obstetric conjugate; posterior sagittal of
the inlet, mid pelvis and the outlet.
General observations can also be made
about the curvature and inclination of the
208
sacrum as well as the appearance of the
sacrosciatic notches.
The anteroposterior film:
This view is taken to measure the
transverse diameter. The divergent distortion
in this view is very com-plicated
and hinders the measure-ment of the
transverse diameter of the inlet, the
interspinous and intertuberal diameters.
These diameters are at somewhat
different levels. The locations of these
levels are also not clearly marked
anatomically. Therefore the use of
isometric scales is very difficult in this
situation. The magni cation factors can
not be eliminated, therefore correct
measurements can not be made.
Fig16.2: Shows X-ray pelvimetry
Thom's Method:
This is quite cumbersome and involves
placing the patient on the X-ray table in
a semirecumbent position. Her back rests
on an especially designed support so that
the patient could be placed at an angle
where the inlet of the pelvis is parallel to
the X-ray plate. The tube-film distance is
kept at 36 inches. The intensity of the
exposure is varied accord ing to the girth
of the patient. The patient is removed
from the table, while the tube and
exposed film is left in place. The