b. The Influence of Abnormal Straightness on the Shape of the Pelvis.— This causes forward displacement of the pelvis, the diameters of the brim not being affected, while those of the outlet are considerably shortened.
B. Scoliosis.
This is a classic deformity of the vertebral column; but we must here make a distinction between rachitic and non-rachitic scoliosis. The lat ter developes slowly, and affects only the spine (Figs. 50 and 51), while in the former the entire skeleton is involved, so that the pelvis and the limbs, as well as the vertebral column, are affected (Figs. 52 and 53), so that women with these two deformities present appearances entirely dis similar. In rachitis the limbs are short and curved inward, the women are not only of small stature, but, by reason of the affection of the tho rax, are small in general. Moreover traces of rachitis will be found in the skeleton, such as are absent in non-rachitic scoliosis. The pelvic deformity is different in the two cases; it may be but slightly marked in the latter, and may occasion but little difficulty during parturition, while in the former the deformity may be sufficient to constitute a formidable complication to labor. Figures 54 and 55, from Tarnier and Leopold, will show the points of difference.
a. Non-rachitic Scoliosia.
The narrowing is rarely so great as to do any more than to somewhat retard labor; the women are usually delivered spontaneously at term.
Hifigoyen notes the following points, based on an analysis of nineteen cases: 1. There is more or less marked flattening of that half of the pel vis towards which the lumbar deviation inclines, or on which the weight of the trunk is thrown. 2. One of the oblique diameters, together with the corresponding sacro-cotyloid distance, is shortened. The symphysis may deviate slightly, so that there is a tendency to the obliquely-oval type. The contraction is confined to the brim, along the curve of the innominate bones, which is the centre of resistance between the trunk and the femora.
b. Rachilic Scoliosis.
Leopold has studied this subject most thoroughly; he has found that this influence is more marked when the individual is attacked with rachitis at an early age, and when she has used her lower limbs. Kehrer
and Engel have shown that a certain number of the peculiarities of shape characteristic of the rachitic pelvis exist in the foetus, or in the infant who can neither walk nor stand; these peculiarities consist in longitudinal and transverse lengthening of the sacrum, in depression of the promon tory forward and downward, curving in of the thigh bones, flattening of the ilia, a uniform or triangular shape of the superior strait, and broaden ing of the symphysis.
Three factors determine the characteristic shape of these pelves, viz.: The pressure and counter-pressure sustained by the pelvis, the traction of the ligaments, and that of the muscles. The degree of asymmetry of the pelvis depends on the degree of the scoliosis. The most striking feature in a scolio-rachitic pelvis is: 1. The forward in clination of the promontory, and the marked shortening of the true conjugate, which varies from two to three and a half inches. 2. The evident shortening of the right oblique diameter of the outlet, which is always shorter than the true conjugate. In the scolio-rachitic the asym metry is shown at the first by an increase of the distance that separates the anterior superior iliac spine from the ischial tuberosity of the same side; the distance between the anterior and posterior spines themselves is increased. The angle formed by the junction of the ischio-pubic rami is greater than normal. Consequently, the true conjugate is shortened as well as the oblique measurements, the symphysis pubis is displaced towards the side opposite to the lumbar scoliosis. As a result, on this side, the distances which separate the superior and inferior borders of the spmph- ais from the posterior superior iliac spines are from one-tenth to foe tenths of an inch less than on the side of the lumbar scolioses. Fins the transverse narrowing of the superior strait, and the inclination of the sacrum on the side of the lumbar scoliosis, cause a shortening of frog 12 to 26 per cent. in the distance between one extremity of the transverse diameter and the promontory, as well as that between the former point and the tip of the sacrum.