An interesting change in the position of the pelvic bones after hip-joint disease, is de scribed by Rokitansky.t .
The dislocation ofthe femur upwards, which is commonly the result of coxalgia, is followed by a wasting of the innominate bones, especi ally of the ilium. They assume a more ver tical direction, and, at the same time, their inclination to the spine, as well as the lumbar curve, is considerably increased.
If this condition be present on both sides, there is general enlargement of tbe pelvic cavity, due partly—to a general attenuation of the bones, causing the disappearance of the projections at the pectineal eminences, the sacro-iliac joints and the cotyloid walls, and partly to a flattening out of the linea in nonzinata. The ischia become dragged out wards and separated, the pelvic cavity shal lower, and the sub-pubic angle more obtuse.
The last resUlt is attributed by Iliilshof to the dragging of the rotator muscles, from the displaced femur on the sciatic tuberosities, upon which the support of the trunk mainly falls in this condition of the joint. In the pelvis of a woman mentioned by Dr. Ilull, however, in whom both the femurs had been dislocated backwards, the transverse diameter of the brim was diminished to 41 inches, and the antero posterior diameter of the outlet was diminished to only 2 inches, from the tilting forward of the lower part of the sacrum, or rather pro bably, from the turning of the lower part of the innominate bones backward by the dis placed femurs, aCting on the axis of the sacro iliac joints.
If the disease be one-sided only, as is most commonly the case, and the diseased joint be much used, the tuber ischii of that side becomes everted, the innominate bone bent outwards, the distance from the pubic sym physis to the anterior superior iliac spine lessened, and that side of the pelvic cavity enlarged. The pelvic cavity is, on the other hand, contracted on the sound side, towards which also the spinal curvature inclines, from the principal support of the body falling on that side. When ankylosis has taken place, the innominate bone is bent outward at the acetabulunt, in the osseous cicatrix ; the ilium is placed more inwards and forwards, and the ischium inwards and backwards ; and while the pubic sy mphysis is drawn towards the diseased side, the sacral promontory is turned to the healthy side of the pelvis. In some
instances, the pelvic inclination is less, instead of greater, on the diseased side, which is also raised higher than the other. This variation is attributed by Guerin to the action of the psoas and iliacus muscles, which sometimes in these cases impress a deep furrow upon the iliac wings, over the edge of which they play. There is no doubt, that the posture to which the patient may have been most ac customed, has a great effect in producing such differences, as already explained in the fore going pages.
of the pelvic bones.—The sacrum, according to Boyer, is less frequently found fractured than the other pelvic bones, because of its .thickness, strength, spongy texture, and deep-seated position. When fractures of this bone do happen, they are most commonly found at the lower part, which is less protected by the above pecu liarities. They occur chiefly from direct and great violence, which generally injures also other parts of the pelvis extensively, seriously affecting the nerves of the sacral plexus, so as to produce paraplegia and retention of urine, as well as extensive injury to the soft parts, such as result in effusion of blood, peritonitis, and sloughing of the integuments. Fractures at the lower part are much more easy to diagnose than those of the upper, which are seldom discovered till after death. In the former case, the lower fragment is generally drawn forwards by the action of the great glutei and coccygei muscles, so as to press upon and interfere with the functions of the rectum, through which it may be felt by the finger. It will also produce great pain on moving the legs, which may lead to its discovery, when more serious injury is not present.