804. 



PELVIS. 



Since we know that the foetus 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 changes usually consequent upon this 

 process in joints such as ankylosis, happening 

 at a period of immaturity, coincident with, or 

 consequent upon, an arrest of development 

 in the structures implicated, and probably 

 having the same ultimate cause. The three 

 cases before 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 separately 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 variations of form than, the defor- 

 mity under consideration. 



The mechanism 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. 



Another form of unsymmetrical pelvis is 

 described by Rokitansky, arising from a coa- 

 lescence of the base of the sacrum with the 

 body and transverse process of the last lum- 

 bar vertebra, on one side the median line only, 

 and the participation of the latter in the for- 

 mation of the sacro-iliac joint on that side. 

 The innominate bone thus obtains a higher 

 degree of elevation, and a greater inclination 

 to the spine, and describes a larger and shal- 

 lower curve of the "linea innominata"than its 

 fellow. The conjugate diameter is rendered 

 greater, and there is a larger capacity on the 

 abnormal side of the pelvic cavity. There is 

 but slight projection of the sacral promontory, 



and the lumbar vertebras are rotated, and their 

 curve inclines to the opposite or smaller side, 

 and may thus produce a lateral compensating 

 curve in the thoracic region. In this latter 

 particular, also, this form of pelvic distortion 

 differs from that described by Naegele, in which 

 the lumbar curve is towards the abnormal side. 

 I have met with two pelves presenting this 

 abnormality. In one, that of a female, which 

 is in the collection of Dr. A. Farre (fig. 124.) 



Fig. 124. 



Oblique pelvis from sacro-lumbar coalescence. 



the left half of the sacral base is ankylosecl to 

 the corresponding side of the body and trans- 

 verse process of the last lumbar vertebra, 

 which are flattened and enlarged so as to as- 

 sume the form of the first sacral, leaving a 

 hole for the transmission of the last lumbar 

 nerve. The lumbar transverse process of the 

 opposite side is bifurcated, the lower division 

 being attached by ligament to the venter ilii ; 

 and the corresponding half of the sacro-lum- 

 bar fibro cartilage remains unossified. The 

 last lumbar spine and laminae are connected 

 with the sacrum by very thin plates of bone, 

 but preserve their own distinct outline. There 

 is no ankylosis of the sacro-iliac or lumbo-iliac 

 joints. The true sacral promontory projects 

 little, but a prominent false one is formed by 

 the last lumbar vertebra. The sacrum is short 

 and small, but presents four distinct sacral 

 holes, and five pieces. The lower part of 

 the sacrum presents an abrupt forward curve, 

 so as to leave, with the shortness of the whole 

 bone, little room for a foetal head, which 

 would, probably, require craniotomy in such 

 a pelvis. There is a slight lumbar curve to 

 the right or opposite side to the lumbar ab- 

 normality. The pubic symphysis, also, is re- 

 moved about i or of an inch to the right of 

 the median line. 



The other pelvis is that of a male, in the 

 Museum of King's College. In this pelvis, 

 there is complete ankylosis of both the proper 

 sacro-iliac joints, preserving behind pretty 

 much the outline of the sacro-iliac ligaments ; 

 and partial ankylosis of the abnormal lumbo- 

 iliac junction, which is also on 'the left side. 

 The true sacrum is large and well formed, 

 and the posterior crest is connected with the 

 last lumbar spine by a thin plate of bone. 

 There is, apparently, no lateral spinal curve 

 in this specimen. 



