In two of the cases of this deformity, there had been present disease of the hip joint, which in one had led to the formation of a false acetabulum ; but this was not, in the opinion of the above-named author, the cause of the oblique distortion. He had never seen the distortion coincident with rickets, though he suggests the possibility of such a compli cation.
Rokitansky also considers this deformity to be a congenital malfbrmation, and not a consequence of fcetal intra-uterine disease.
Dr. Knox adopts the theory that the arrest of development having taken place while the ossification of the sacrum was in complete, the whole of that side of the pelvis remains thereafter stationary in its fcetal or brute transitional form, while the other ad vances to complete development ; and thus one side is perfect, while the opposite is simply that of an undeveloped pelvis magnified. This anatomist also states, that in the mu seum of Dr. Outrepont there is a female pelvis presenting the oblique deformity on both sides, producing a superior opening of a very elongated shape, with its broadest part towards the sacrum.
The lateral epiphysial sacral pieces, which form the auricular surface, appear in the ob lique deformity to have failed in establishing a separate identity, though the presence of the sacral holes and transverse lines and grooves lead to the supposition that the number of the primary ossific points has been normal. Un der this supposition, the coalescence of the sacrum and ilium would, probably, take place between the sixth and ninth months of intra uterine life, (at which time the characteristic ossific points of the three first sacral vertebrm begin to appear,) by the prolongation into them of the ossifying process from the ilium or " pleurapophysis," already considerably ad vanced in its bony development.
Another hypothesis as to the cause of the anky losis, is found in the occurrence of in flammatory disorganisation, after the com plete formation of the sacro-iliac joint, and, as a consequence, oblique deformity of the bones. Dr. Rigby inclines to this theory, and thinks that ulcerative absorption must have existed in the joint, though probably in early life.
Since we knoiv that the fcetus in utero is subject to similar pathological changes to those of childhood, it seems probable that a modi fication of the two theories may be the true statement of the origin of this formation —viz.,
an occurrence of inflammation and the patho logical champs usually consequent upon this processin joints—such as ankylosis, happening at a period of iminaturity, coincident with, or consequent upon, an arrest of development in the structures implicated, and probably havino. the same ultimate cause. The three casesbefore quoted from Naegele, in which the deficiency of the sacrum and the oblique deformity existed, but without the ankylosis, and on the other hand,the many cases in which we have ankylosis on one or both sides with out the oblique deformity, show that the two conditions may occur separatel3 and indepen dently of each other. These cases also prove beyond a doubt, that the sacro-iliac ankylosis of itself does not produce the deformity; and, moreover, that it is not absolutely an essen tial, although a frequent accompaniment of this peculiar formation.
A third supposition alluded to by Naegele, that the ankylosis and oblique distortion is caused by increased pressure from the lateral divergence of the vertebral curve in early yOuth, seems to be contravened by the fact, that such a pressure does not produce such a result in the many instances of other pelvic deformities.. The tendency to an unsym metrical one-sided distortion in the instances before alluded to, presents many differences to, and more variation's of form than, the defor mity under consideration.
The mechanisnz of this deformity in re spect to the line of gravity of the body fall ing nearer to the acetabulum of the anky losed side, and so throwing the weight of the body more on to the corresponding leg than on its fellow, will present some similarities to that of the one-sided pelvis just mentioned ; with this exception, that the bones of the obliquely ovate pelvis are healthy and not softened, and that the lateral pelvic arch is, consequently, flattened only, and not indented, the principal yielding and inward bend appear ing to take place at the abnormal sacro-iliac junction, and thus the antero-posterior dia meter—i. e. from the sacral promontory to the pubic symphysis—is increased and not dimi nished.