Causes of the foregoing pelvic distortions. — The principal causes of the preceding partial and complete distortions of the pelvis, are two diseases affecting the osseous system ; viz. " rickets"—and " mollifies ossium" or " malacos teon." Rickets is a very common disease of early life, which is said to be more apt to occur in scrofulous children about the period of denti tion, but which may occur even after puberty, according to some authors. It is characterised by a simple deficiency of the earthy matter of the bones—chiefly of phosphate and carbonate of lime ; while the animal constituents, al though softened, and rendered less elastic, retain nearly their normal composition. The bones thus rendered pliable, which lie in the lines of weight, pressure, or muscular action, yield slowly and give way to the operating forces, bending in such a manner as the re sultant direction of pressure and muscular traction, &c., permits them.
We must refer the reader to the Article on the PATHOLOGY OF BONE (V01. i. p.440.) for a more detailed account of this disease.
In Rokitansky's Pathological Anatomy, the bones in Rhachitismus infantalis are described to present two separate pathological conditions. In one, the bones are very vascular, soft, fragile, and swollen, with enlarged medullary cavities, and the areolar spaces filled with, and often distended by, a pale, reddish jelly, which press in.. upon the areolar partitions, produces their absorption, and thus the enlargement of the cavities by coalescence. This jelly is also sometimes found effused under the periosteum. In the second variety, the bone is more or less reduced to its cartilaginous elements, the corpuscles (lacuna.) empty, the rays obliterated, and the lamellar structure wanting, or fallen asunder,'. with corpuscles interposed between the layers. On the last condition the softening of the bones de pends. The periosteum is more vascular than normal, tumid, and more closely adhe rent, so as to tear off with it a portion of the softened adjacent bone. It is said to differ from inalacosteon in not being a painful disease, and in being capable of cure, with a subsidence of the swelling and reabsorption of the effused substance. In high degrees of the disease, however, atrophy and fragility re main permanently. The osseous structures affected by rickets are lighter, less marked, thinner, and more porous than normal, or than those affected by mollities ossium, according to Naegele ; — appearing as if they had been steeped in weak acid.
In the humerus, also, vvas found 10-54 -per cent. of fat. Specific gravity of the bone, 0.612.
Davy found in 100 parts from the tibia of a rickety child, 74 parts animal and 26 earthy ; and Bostock, in a vertebra affected with the same disease, 79-75 animal, and 20-25 earthy, in 100 parts.
When this is contrasted with the norma proportions of the OSSCOUS constituents in the child, as given by Schreger — viz. 47-20 parts animal, and 48-48 earthy (or about one half even before incineration, left, after exposure to a red heat for some time, a very porous and light inorganic structure. The following results were obtained by thus burning off the organic coinponents-100 grains of bone,— From the body of an upper lumbar verte bra left—of earthy ?natter - - 31„ the last lumbar vertebra - - 27 „ lower end of the sacrum - - 24 „ ilium (cotylo-sacral rib) - - 40 „ ischium (near tuberosity) - 36 „ pubes (near acetabulum) - - 33 11 of the femur - — 22 „ neck of the femur - - - 25 „ shaft of the femur (below trochant) 58 When we compare the foregoing propor tions of the two constituents of bone with those given by Schreger, as the normal pro portions of adult bone — viz., 20'18 animal, and 74-84 earthy matter—the diminution of the inorganic constituents appears very striking, and still greater when compared with those of aged bone ; although less so than in the re sults of the analysis of Dr. Leeson, in the extreme case recorded by Mr. Solly before given.
The femurs were perfectly normal in shape, as also were the bones of the lower leg, but the pelvis was a rostrated one, the superior pubic rami being bent in the middle nearly at right angles, and much deformed and con tracted in all its diameters. It was remark able, that, at the bend of the superior pubic rami, and at the suture of the ischio-pubic rami, there was a complete deficiency of osseous matter, so that after maceration, the pubes separated at these points ; showing that the connection and continuation of the bone in these places was purely ligamentous, or by organic matter, as if resulting from an un united fracture.
The sudden diminution of the hard con stituents in the head and neck of the femur, as compared with its shaft, is worthy of ob servation 'in reference to the bending and fracture of the femoral neck in old people.
The smaller proportion of earthy matter in the pubes, as compared with the ilium, and in the sacrum and lumbar vertebrw, as com pared with the femoral shaft and pelvis, will account for the greater yielding and deformity which are observed in these parts in the angular pelvic distortion, especially in the rostrated variety, and will be referred to pre sently in the consideration of the mechanism of pelvic deformities.