Depaul says: " We must not take in too strict a sense the expressions ' uniformly contracted,' and ' regularly narrowed,' employed by writers to describe this variety of deformity. I have several pelves in which the diameters are all shortened, and the entire pelvis is quite regular. But, while the transverse diameter of the brim is shortened by only three-fifths of an inch, the shortening of the antero-posterior reaches one and three fifth inches, so that the pelvis as a whole is evidently flattened from before backward, and may strictly, by reason of its regular shape, be included among the rachitic pelves." Those obstetricians who have affirmed that such pelves resemble the male type are incorrect; they differ from the latter in the slight projection of thin, bony prominences, the slenderness of the bones, the divergence of the pelvic arch, the size and depth of the iliac fosse', and finally, by the relatively increased capacity of the true and false pelves.
The cause of this deformity is still uncertain. Depaul regards it as " a freak of nature, the cause of which is as difficult to understand as is every other defect in proportion in the skeleton." Diagnosis.—This can be positively made only by the vaginal touch.
Prognosis.—It is very grave, since in thirteen cases observed by Lubac, ten women died and only three infants survived. It is so much the more serious, as there is nothing in the woman's stature to point to contraction, and the deformity is only recognized during labor, in consequence of the obstacles that prevent its progress. The prognosis varies according to the time at which we are summoned to interfere. In our two cases, both pa tients survived, one being delivered, spontaneously at the seventh month, while in the other artificial labor was induced at the eighth.
II. Irregularly contracted Pelvia In this, which is the most common form, the contraction may exist in one or all parts of the pelvis. Although the variations are numerous, three fundamental types exist, viz.: 1. Shortening of the antero-posterior diameter, resulting in flattening from before backward.
2. Shortening of the oblique diameters, causing sinking in of the antero lateral walls.
3. Shortening of the transverse diameter, producing flattening or com pression of the sides.
If the contraction is situated at the superior strait, it causes approxi mation of the anterior and posterior walls, while the rest of the cavity may be of normal size, or even enlarged; or the inferior strait may be in volved, or both together, so that pelves of various shapes may exist (cor date, reniform, etc.). The deformity may be confuted to the sacrum or symphysis.
a. The Sacrum.—The sacral curve may be exaggerated, the base of the bone projecting so far forwards as to increase considerably the promi nence of the sacro-vertebral angle; sometimes the sacrum is entirely flat, or its concavity is replaced by a convexity, the line of junction between the first and second vertebrae being so marked as to resemble a second promontory, the entire sacrum appearing to be moved forwards. Or, on the other hand, the sacral curve is exaggerated to such a degree that the bone seems to be bent upon itself; as a result we have increased projec tion of the promontory and base of the sacrum, narrowing of the superior and inferior straits, and enlargement of the cavity. Sometimes the sa crum appears to rock upon itself in such a manner that the base approaches the symphysis, while the lower extremity recedes, causing narrowing of the superior strait, with enlargement of the lower portion of the cavity and the outlet.
b. Symphysis Pubis.—Instead of being convex, it may be flattened, or even convex posteriorly, forming the " figure-of-8 " pelvis. The mail) pelvis is then contracted (flattened pelvis); or the symphysis may be broader than normal, being more inclined from before backwards, or from behind forwards.
c. Coccyx. —Anchylosis of the coccyx may cause variations in the antero posterior diameter of the outlet.
There is another change which affects the superior strait, due to spondy lolisthesis. The promontory is then formed, not by the sacrum, but by one of the lumbar vertebrte, and the brim is thus contracted, some times to an extreme degree. In some instances the symphysis is flattened by reason of the compression of the horizontal rami of the pubes, so that the latter become parallel and juxtaposed. The symphysis assumes the shape of a duck's bill, and, since the gutter formed by the approximation of the pubic rami is useless during labor, there results very marked short ening of the antero-posterior diameter of the pelvis, both at the brim, and in the cavity. (See Osteomalacia.) When the shortening of the oblique diameters is -produced by compression of the antero-lateral walls, it may exist on one or both sides; this is due to flattening of the femur, and even projection of this bone into the pelvis, at a point correspond ing to the bottom of the cotyloid cavity. As a result, the normal curve of the superior strait and cavity disappears, the hip-bone becomes flattened and straightened, the pelvic curve convex, and, when both sides are com pressed, there is shortening of all the diameters of the brim and outlet, so that the pelvis assumes a trefoil shape. This compression is often confined to one side, at least the deformity is more marked on one than on the other (oval, or obliquely-oval pelvis). Rarely the transverse diame ters are shortened, from atrophy or non-development of the ilium, or be cause the latter is pressed towards the median line. The shortening is usually confined to the transverse diameters of the cavity and outlet (fun nel-shaped pelvis). All these varieties may be combined, giving rise to complex forms; such pelves may, however, be classified according to the causes that have produced these deformities. But, in addition to those special causes, which we shall study a little later, there are three factors which affect the entire pathology of the pelvis, and these deserve some attention. As Schroeder says, in order to account for the deformities of the pelvis, we must go back to the new-born infant and study the agents that transform its pelvis into the adult form, because these will subse qUently produce the various malformations, whenever there exists soften ing, or pathological changes in the pelvis. These causes are the pressure of the trunk, the mutual traction exerted upon each other by the iliac bones at the level of the symphysis pubis, and the counter-pressure of the femora. The weight of the trunk tends to force the sacrum down wards into the pelvis, but since the centre of gravity of the trunk falls in front of the sacro-iliac articulation, the sacrum rotates about its axis, so that the promontory tends to sink into the pelvis, and the tip of the sa crum to point directly backwards. But the extremity is firmly fixed by its ligaments, so that the sacrum is curved from above downward. On the other hand, while the sacrum has a tendency to sink into the pelvis, it produces, through the medium of the sacro-iliac ligaments, considerable traction upon the posterior superior iliac spines. As the latter, accord ingly, approached each other behind, their pubic ends would be drawn apart in proportion to the amount of traction exerted posteriorly; hence there occurs an antagonism of forces, which results in the curving of the bones at the point of least resistance, that is to say, at the level of the articulation. This curve is a regular one according as the upward pres sure of the femora upon the bottoms of the cotyloid cavities is added to the traction, in an opposite direction, made upon the anterior and posterior extremities of the iliac bones. If these three forces act regularly, simul taneously, and in proper proportion, we shall have a normal pelvis; if one or the other force predominates, the result will be a deformity which cor responds to the character and intensity of that force.