Character Of Lesions

The lesions in rickets may be summed up in the statement that the preparatory stages of ossification are exaggerated, while the completion of the process is delayed.

At the ossifying; cartilaginous border the conditions may be studied by examining Fig. 267, and comparing it with Fig. 266, which represents normal ossification, both figures possessing a similar degree of magnification. The most pronounced difference from the normal is the enormous exaggeration of the zone of multiplication of the cartilage cells (a, a). The groups of cells are in much larger numbers and occupy a much greater space; at the same time they have not always the normal arrangement in rows parallel to the long axis of the bone. The cells of the groups also vary considerably in size. In the normal bone the cells in the deepest part of this zone are large, but in rickets, while some are large, as at b, there are others even at the same level, or deeper, of small size.

Next, in regard to the zone in which the cartilaginous matrix becomes calcified, this also is represented here in the most irregular fashion. Calcification of the matrix occurs, and calcification of the cartilage cells (as at b on left), but it is very irregular. There will be calcification of the cartilage high up, as at b, while there are numerous groups lower than that uncalcified. In many cases also, whether calcified or not, the cartilage cells lose to a considerable extent then grouping into rows (as below b on left).

Then as to the formation of medullary cavities and development of bone, the figure shows how irregularly this occurs. Blood-vessels appear with considerable frequency in the midst of the cartilage, and towards the deeper parts there are medullary spaces with osteoblasts in them. These may even be seen forming new bone, as at d. But the medullary cavities do not occur with any greater regularity than the other stages in the process, and it is not always apparent that they have to do with the formation of the bone. It will be seen in the figure that at a certain somewhat indefinite level, which is lower at the left side than at the right, bony trabecular appear (c, c). But it will also be seen that the bone is directly continuous with cartilage, the difference in the two being indicated chiefly by the difference in the cells. It appears also that in the cartilage, which is thus immediately continuous with the l>one, the individual cartilage cells are separated by a matrix just as the bone corpuscles are (see figure). In fact there is here a conversion of cartilage into bone, and there are even appearances suggestive of the gradual transformation of cartilage cells into bone corpuscle's. It will be seen in various places, but especially at d, that pieces of cartilage survive in the midst of the new-formed bone. Such cartilage may be calcified or not.

Fig. 261. - Longitudinal section of ossifying margin of a long bone in rickets: ft proliferating, cartilage cells, the area of these very greatly extended and the arrangement quite irregular; b, bf calcification of the cartilaginous matrix at different levels, but not followed by formation oe medullary cavities. The formation of medullarv cavities (e, e) and of bone is occurring quite irregularly, the level being higher at the right"(c)than at the left (c). At d the osteoblasts ar forming bone. In various places, especially at d, pieces of cartilage are seen in the midst of bone, and an apparent transition of the one into the other is seen, x 90. (Thierfelder).

To the naked eye the changes described above are indicated in a, longitudinal section of a rickety long bone. The blue zone, which forms a straight narrow transverse line in the normal bone, is here greatly increased and its boundaries are irregular. The yellow zone of calcification of the cartilage is still more irregular, and yellow pieces crop up in the midst of the blue zone. Blood-vessels appear also at different levels. In the area of the blue zone the cartilage is greatly swollen, as the enormously multiplying cells take more space than normal.

Under the periosteum the normal thin layer of osteoblasts is increased till it forms a layer of considerable thickness. Bone is formed to a very limited extent and very imperfectly, so that instead of a proper dense bone, such as should be formed on the surface of the shaft, there is a loose irregular spongy bone. But even the trabecular of this spongy bone are not properly formed. Immediately under the thick subperiosteal layer the new-formed bone does not show in its matrix the homogeneous character of the matrix of bone; it is granular,, and the lime is obviously deposited without combining with the matrix in the normal manner. It is a calcification rather than an ossification, and the trabecular are rather osteoid than osseous. On passing inwards the tissue becomes more strictly osseous however, although hardly acquiring the regular arrangement of the dense bone of the shaft.

Corresponding with the structure described are the naked-eye characters. The subperiosteal layer is seen in the form of a red vascular layer of some thickness. This is so obvious in some cases that, at one time, it was described as if a blood-clot were formed under the periosteum. Beneath this the spongy character of the bone can be seen, while the shaft is considerably thicker than normal and obviously more easily bent.

Deformities Of The Bones Due To Rickets

In considering the deformities so often produced by rickets, it is to be remembered that the two chief changes in the bones are, in the first place, enlargement and softening of the epiphyseal extremities of the bones from the affection of the cartilage, and, in the second place, thickening with loss of resistance of the shaft from the periosteal lesion. These conditions do not always go strictly parallel, one or other being frequently the more prominent in a particular bone. The various bones of the body also present very commonly different degrees of rickets, although the disease, being a general one, usually affects many bones. Even in bones affected to a similar extent, however, the resulting deformities present very great variations; the deformities consist largely of curvatures of the bones from the application of external forces, and the bones are differently placed in relation to such forces.