TUBERCULOSIS OF BONE.
In Chapter IX, on Tuberculosis in general, we entered into considerable detail in regard to the nature of tuberculous lesions, which were stated to be essentially the same whether occurring in hard or soft tissue, the active agent being the now well-known Bacillus tuberculosis, which, finding lodgement, for instance, in the osseous tissue, acts as a specific irritant, and so provokes the production, first, of a typical tubercle, and, later, of typical granulation tissue, by whose ravages the distinctive signs of bone tuberculosis are produced. This process, then, is in no respect different in bones from similar lesions in other parts, though modified to a slight extent pathologically, to a greater extent clinically, by the dense environment. Nevertheless, trifling or most extensive destruction of bone substance is produced by this tissue, while by continuity or by metastasis there is more or less involvement of the adjoining textures, either parosteal or articular. It is by granulation tissue that so-called caries is produced, and it is by the same tissue that distinct portions of bone are sometimes completely segregated from their vascular surroundings and shut off from nutrition, so that they die and form what are known as sequestra. Necrosis may then be the result of tuberculous disease.
PLATE XXXVI
Tuberculous Disease of Hip-joint and Pelvis, involving the Muscles (rare). (Lannelongue.)
o, rarefying ostitis (i. e., osteoporosis); f, fungus granulation tissue.
So long as the process is active, this granulation tissue tends to enlarge its boundaries, and, like pus, to spread in the direction of least resistance. When produced in the shaft of a long bone this may lead to involvement of the entire shaft, or there may be liquefaction and absorption of dense bone and the formation of a sinus from the marrow cavity to the periosteum, beneath which the granulation tissue will spread, and through which it will sooner or later perforate, to resume its progress toward the surface, always in the direction of least resistance. In this progress tendon sheaths or bursæ may be involved, or dense aponeuroses may turn the granulation column aside, causing it to perforate toward the surface at some remote point; while it may spread out more or less beneath the skin before finally causing its destruction. Sooner or later, if uninterrupted by treatment, this escape will occur, and then we have the condition of a tuberculous ulcer of the skin, from which leads down, by a devious path, a sinus toward the original focus.
When this original focus has been juxta-epiphyseal there is involvement of the epiphyseal cartilage and a pathological diastasis, which may early lead to spontaneous or pathological luxation. Or, again, a focus having once originated at an epiphyseal extremity, tends usually to perforate quickly into a joint cavity, after which a considerable length of time is usually expended in filling up this joint cavity with exuberant granulation tissue. This is the material so often found in tuberculous joints, and is well characterized by the name given to it by the Germans, fungous tissue, they calling such joint affections fungous joint inflammations. (See [previous chapter].)
Seen thus in joints, after it has been long exposed to friction and to more or less pressure, it may have lost some of its original luxuriant features. It is best seen when it is freshest and has been exposed to least disturbance. Under these circumstances it is vascular, dark red in appearance, friable, and easily removed from the tissue upon which it has grown. Ordinarily it is infectious, and by its inoculation into animals is capable of reproducing the disease.