Inflammation of bone (ostitis) is sometimes evidently the result of external causes, of various injuries, for example, most of which have been already enumerated, of concussion of the bone, or of cold; sometimes it arises from internal conditions, as when some constitutional affection, whether syphilis, the mercurial cachexia, scurvy, gout, and the like, or an exanthematous process, fixes itself in a bone. But the etiology of inflammation of bone is a subject which requires, more than many others, to be cleared up.

Moreover inflammation of bone is frequently a secondary disease propagated from neighboring tissues, especially from the periosteum.

It is sometimes an acute inflammation, especially when produced by external injury; very frequently it is chronic, and is almost always so when it arises from any constitutional affection. It is sometimes confined to one bone, or to one circumscribed spot on a bone; sometimes it attacks several bones, or most, or nearly all of them, not perhaps all at once, but one after another in more or less rapid succession. At one time it affects the outer layer of a bone, and is combined with periostitis; at another the inner strata, when it is associated with inflammation of the medullary membrane: the accompanying inflammation of the periosteum and medullary membrane may be an original part of the inflammation, or a later addition to it. Lastly, there is a third case, in which a bone is inflamed in its whole thickness: in some instances it is so from the first, in others the inflammation reaches that extent later in its course.

It is situated sometimes in compact substance, in the compact portion of a bone; sometimes in spongy substance, in spongy bones, and spongy parts of bones; and, external causes being excluded from consideration, the selection of its seat depends in a remarkable manner on the constitutional affection which gives rise to it, a peculiar preference being manifested sometimes for one portion of the skeleton, sometimes for another, and sometimes for particular bones. Inflammations of bone vary much, and, in a practical point of view, materially in the degree and nature of the inflammatory process; and exhibit it first in the composition of their product (the exudation), and then in their consequent terminations. It would be inconsistent with nature, and in fact impossible, in an anatomical delineation of inflammation of bone, to make a broad division of it into acute and chronic; I shall, therefore, be careful only at the proper points to mark the transitions of one into the other, and the characteristics by which they are distinguished.

A Very Moderate Degree Of Inflammation

Very Moderate Degree Of Inflammation, in the outer lamella of a bone, for instance, produces a gelatinous, dark-red exudation, which gradually changes its color to bluish-red, yellowish-red, and reddish-white, and at length becomes quite white: at the same time passing from its original gelatinous condition, it forms a coagulum like white of egg, then becomes a soft, flexible cartilage, and, finally, reddish-white, succulent bone. In this state it invests the bone, and constitutes, according to its quantity, either a white, porous, and scarcely perceptible film, or a thicker layer, that resembles fine felt or velvet. The periosteum appears at first injected, bluish-red, infiltrated, and decidedly swollen, and generally has but a loose connection with the exudation; for the latter, especially after it has ossified, adheres somewhat closely to the bone: sometimes, however, when the periosteum is peeled off, part of the exudation comes away with it. There is no change in the bone till the process is advanced, and then its grooves and the pores for its vessels are manifestly widened. The ossified exudation afterwards unites with the surface of the bone, and either forms uninterruptedly an addition to the thickness of the compact wall, or is connected with it by a layer which remains spongy (diploetic). In some of the thicker layers of bony exudation, occasional voids of various dimensions are met with, which are filled with a vascular tissue containing medulla: they may, on the macerated bone, be easily taken for the losses of substance produced by caries; but without doubt they are merely the result of absorption in bone already formed, and are analogous to the formation of cancellous tissue, and a medullary cavity in callus. (Compare with this and with the following, what has been said on the subject of the osteophytes).

The principal opportunities of seeing this process are obtained in the neighborhood of more intense spots of inflammation, and around caries.

The inflammation may recur in the exudation at any period of its ossification, and lead to a corresponding increase in the size of the bone.

There are other inflammatory processes, some of them more acute, which return from time to time, and appear to be of a specific nature. Like those already described, they extend sometimes to several bones, and they deposit abundant exudations, which may assume the form mentioned above, or the various other shapes delineated in the section on the osteophytes: the periosteum, at the same time, becoming hypertrophied, acquires a fibro-lardaceous, callous structure, and sometimes an enormous thickness.

An inflammation of this kind may be often observed beneath chronic ulcers on the inner surface of the tibiae. The periosteum and adjoining cellular tisue, having been converted into a lardaceo-callous substance, form the base of the ulcer, and cover a luxuriant growth of curled bony plates, like madrepore, which are arranged perpendicularly upon the bone: the periosteum sends processes between, and forms sheaths around the separate plates. A villous, or a spavined and laminated, osteophyte is usually seen in the neighborhood, and hence, as the new tissue becomes indurated, a circumscribed portion of the bone is increased in bulk.

When the inflammation is seated in the inner lamella of a long bone, or in the diploetic substance, it pours forth its product on the inner surface of the medullary tube, or on the walls of the cells of the spongy substance; and the tube becomes narrowed, and the spongy substance condensed. The process of exudation very often occurs on both the outer and the inner lamella of a bone together; and sometimes the intermediate substance also shares in the process, and the ossifying exudation, deposited on the walls of the Haversian canals, produces induration (sclerosis) of the bone.

Besides these there are, no doubt, inflammations of bone, especially such as are slight in degree, and chronic in their course, which give rise to products that become organized in various other ways. Some change into osseous substance, the texture of which deviates from that of healthy bone; while others form fibroid, or cellular tissue, or a substance which resembles the jelly of spongy bones. Such products occasion a loosening and expansion of the bone proportioned to their quantity; and many of the osteoporoses, which are attended with increase of the volume of the bone, are, no doubt, due to such processes of inflammation, or as they are called, irritation.