Orthographic Pelvimetry

Abstract

BY ORTHOGRAPHIC pelvimetry we mean the production of true dimensional tracings or orthograms of the frontal and lateral views of the pelvis, on which one can measure the transverse diameter of the inlet, the interspinous diameter, the intertuberous diameter, the obstetrical conjugate, the anterior and posterior sagittal of the mid pelvis, the anterior and posterior sagittal of the outlet, and numerous other dimensions, without the aid of computations or specially calibrated rulers. Pelvic orthograms have been used to some extent in the past by van Ebbenhorst Tengbergen (1), Litwer (2), and Thoms (3). Some years ago, one of us (Hodges), reviewing with Dippel the development of roentgen pelvimetry (4), referred to a 90° triangulation apparatus then about ready for publication and discussed the possibility of developing a linkage pantograph for the making of frontal and lateral orthograms from the pair of 90° roentgenograms that would be produced by that apparatus. During the war the facilities of our laboratory were diverted into other channels, but recently we have completed the apparatus and have devised and constructed the proposed linkage pantograph. With two of our colleagues at the Chicago Lying-In Hospital, we are using this apparatus for pelvic mensuration in 1,000 primiparae and expect eventually to publish our findings relative to the dimensions of the pelvis in eutocia and in dystocia. In the present paper we shall deal merely with the technical details of orthometric pelvimetry. Our 90° apparatus and pantograph were shown in the scientific exhibit of the Congress on Obstetrics and Gynecology in St. Louis in September 1947, but no account of them has heretofore been published. The 90° Apparatus A motor-driven reciprocating Potter grid and an x-ray tube are attached to a cradle that is mounted beneath the 24 × 84-inch top of a special x-ray table (Fig. 1) which has a 6 × 231/2-inch notch cut into its right side to receive the grid during the making of the lateral film. The grid-tube assembly may be rotated so that the tube lies above and the film below for a frontal view (Figs. 2 and 3) or so that the radiation is directed parallel with the floor and the grid is pressed against the side of the patient for the lateral projection (Figs. 4 and 5). In this latter position the grid may be moved inward toward the midline of the table or outward away from that line, the amount of such movement being indicated on the H (horizontal) scale. It may also be moved up so that the longitudinal axis of the lateral film moves away from the table top, or downward toward it, the amount of this movement being indicated on the V (vertical) scale. A stripe down the center of the table locates its midline, and lead wires embedded in the bakelite top of the grid indicate the longitudinal and transverse axes of the films.