To apply the apparatus, the woman lies on her back, the thighs flexed, and abducted, the knees flexed. The plane is placed so that it rests at its extremities on the anterior superior iliac spines, its centre being over the symphysis. (Fig. 11l.) The two rubber bands, passing behind the pelvis at the level of the crests, and tied together, hold the apparatus symmetrically in place. The free end of the pelvimeter is then inserted into the vagina and placed on one of the bony prominences which we de sire to compare with the other, and then we read off the angles registered by the three circles. To find the point of the symphysis nearest the - promontory, the free arm of the lever is bent to 60°, and then we may touch this point with the lever. We may thus obtain the extreme points in the pelvis, and from these the distances are calculated. (For the method, the curious reader is referred to Kfistner's description.) Kfistner insists on the simplicity of this method. We are sorry we cannot agree with him.
C'rouzat's Pelvimeter.—In 1881, Crouzat proved that digital mensura tion was open to serious error, that is to say, in the estimation of the least sacro-pubic diameter there might be an error of 1.5 to 2 inches in two cases out of three. To remedy this possibility he devised an instrument to be used as a direct pelvimeter. It is composed of two portions, a blade, and a graduator. (Figs. 112, 113, 114, 115.) The blade is of steel, round, 8 inches long, including the finger holder, and .2 inches thick. The nail rests at 0. The blade is graduated in hundredths of an inch, the zero being at 0. The graduator (CC') (Fig. 113) is 3.9 inches long, and at each end is a graduated arc of a circle. The larger arc (A) measures 1.5 inches in height, and the smaller (a) 1.1 inches. The one or the other is used according to the elevation of the post-pubic point. The curvature of the two arcs is the same, belonging to an arc of a circle of 3.12 inches in diameter. In figure 114 it is seen that the arc is hollowed out in its centre to diminish the contact surface. On the horizontal rod of the graduator is the slide (G) 1 inch long. This may be placed at one or another end, and fixed there at i.
Use of Instrument.—The bladder and rectum having been emptied, the woman is placed in the obstetriCal position, the buttocks elevated, the thighs separated, the feet resting on two chairs. The operator stands between the patient's legs, and makes a careful vaginal examination, in order to locate the promontory, and to find the situation of the post-pubic point. According to the height of this point, he chores the smaller or
larger arc. The right index is then inserted into the holder, and is ried into the vagina to the promontory, the chosen arc being, at the same time, carefully placed behind the symphysis. The graduated distance is then read off the horizontal bar, and this is the exact measurement of the least promonto-pubic diameter, inclusive of the soft parts.
Digital Pelvimetry.
As Depaul well says, " notwithstanding the partial advantages offered by the pelvimeters, they one and all are open to objections which render them useless in routine practice. Of all the methods of measurement, that by the hand is certainly the least uncertain, inconvenient, and most exact in its results. We may thus measure the conjugate, and appreciate with sufficient exactness the length of the transverse and of the oblique diameters of the superior strait. All the more readily, of course, in the cavity, and at the inferior strait. Further, thus exostoses and tumors may be readily recognized. This is the method of mensuration almost entirely used in France, and abroad the tendency is to return to it. We certainly do not thus attain mathematical results, but the expert obtains figures precise enough for practical purposes." While in Germany the left hand and two fingers are used for mensura tion, in France the right and one finger are resorted to; only in exceptional cases is it customary to use two or more fingers, or the entire hand.
The woman should occupy the dorsal position, the nates resting on a pillow. The index is carried upwards and backwards to the sacro-verte bral angle, which is readily recognized by its projection, and the trans verse depression at the sacro-lumbar articulation. (Fig. 116.) We must not confound with the promontory, the projection which the first mcral bone sometimes makes over the second, and to avoid this the finger should be carried as high as possible. The promontory once found, the end of the index is placed upon it, and the wrist is lifted upwards, until it rests under the inferior margin of the symphysis. The index of the other hand is then placed against the first, just under the symphysis. The vaginal finger is then removed, with the other in place against it, and then the distance from the point of the index to the position of the second finger may be measured, and we have the exact sacro-sub-pubic diameter.