This is an exceedingly frequent affection, and one attended usually by very serious results. The lesions to be here described are not universally recognized as tubercular in character, although, as observation widens, the dissentients from this view diminish. The term Scrofulous is here, as in other structures, equivalent to tubercular. Caries is another term which, as will be explained below, is nearly equivalent to certain forms of tuberculosis.

Causation

The tubercle bacillus in most cases reaches the bones by the blood. In a large proportion of cases both joints and bones are affected, and it is not determined to what extent the one or the other is the primary seat. It is demonstrable that primary disease of the bones frequently extends to the joints, and it may afterwards attack other bones entering into the articulation. On the other hand when primarily affecting the joint it may extend to the bones concerned in the joint. It is probable, however, that in the great majority of cases the bones are primarily affected, although the lesion in the bone may be so small, and the parts so altered by subsequent changes, that it may be difficult to demonstrate the exact commencement.

The tuberculosis begins in the spongy parts of the bones. It is very •common in bones which are largely composed of spongy tissue, as the vertebrae and the bones of the hands and feet, while in the long bones it affects chiefly the articular extremities. In the case of the vertebrae, it mostly affects simultaneously the proximate surfaces of two bodies (see Fig. 280), as if it took origin in the intervertebral cartilage. In this respect the author's observations correspond with those of Wilks and Moxon.

While spongy bone evidently forms a favourable nidus for the tubercle bacillus, there are two further predisposing elements frequently traceable. Tuberculosis ismostfrequentin young persons, the actively growing boneapparently predisposing to it. This applies especially to the bones of the extremities, and to a less degree to the vertebrae. Injury is the other predisponent. This is a fact of clinical observation which has been confirmed by the experiments of Schuller, who found that after injecting tubercle bacilli into the blood, he could induce tuberculosis of the joints by inflicting injuries such as otherwise would be readily recovered from.

Characters Of The Lesion

The tuberculosis affects primarily the soft tissue or medulla contained in the meshes of the cancellated tissue, and secondarily the bony trabecule. The spaces become occupied by round-celled or granulation tissue, in which tubercles of typical structure are visible. The granulation tissue eats into the bony trabeculae, so that the latter may be entirely destroyed in the affected area. More frequently necrosis occurs in the tubercular new-formation before the bone is entirely destroyed. The form of necrosis is caseation, and in a case of any standing the presence of the disease is evidenced by the presence of yellow caseous matter occupying a certain portion of the cancellated tissue. This is shown in Fig. 280. In this area there are the thinned remains of the bony trabecular, which are also necrosed. As the disease is an advancing one, the more recent affection will extend beyond the caseous area.

Tuberculosis of vertebras.

Fig. 2S0. - Tuberculosis of vertebras. The intervertebral cartilage is destroyed, and the disease, as shown by the white colour (due to caseous necrosis), is invading the bodies. In the upper there is a small isolated patch.

Acute curvature from tuberculosis.

Fig. 281. - Acute curvature from tuberculosis. The bodies of two vertebras have been destroyed, while the ones above and below have coalesced at a. The spinous processes are also anchylosed.

The bone so affected has lost much of its mechanical power of resistance, so that in the case of the vertebrae the bodies collapse and lead to acute curvature, as in Fig. 281, while in other cases the bones are eroded and worn down by the friction at the joints. In some cases the necrosis leads to the formation of a Cavity in the bone. This may be from softening of the caseous tissue, but in some cases the necrosed piece is separated as a kind of Sequestrum which may be found lying in the cavity. In either case the walls of the cavity are lined with tuberculous granulation tissue. In the case of small bones, such as those of the foot or hand, which are thus excavated, there may be a complete collapse of the bone, so that it is more or less destroyed.

It is to certain of the conditions indicated above that the term Caries is sometimes applied The characteristics of caries are, rarefaction of the bone, which here is produced by the encroachment of the tuberculous tissue; undue softness of the bone, so that it is eroded and generally exposed at an articular surface or in the wall of a cavity; the presence of caseeous matter, along with prominent and flabby granulation tissue, whence the name Fungous caries. (See further under Diseases of the Joints).

Tuberculosis of vertebrae with abscess.

Fig. 282. - Tuberculosis of vertebrae with abscess. The trachea is laid open in front of the oesophagus. It is markedly narrowed where the aorta crosses in front of it, being there compressed between abscess and aorta. The abscess has extended upwards and downwards in front of the vertebrae, impinging on the oesophagus. Through the Litter a piece of whalebone has been passed.

The tuberculous bone is a centre of irritation, and there usually follows a suppurative process which is frequently slow in developing. The resulting Cold abscesses (see Fig. 282) are most typically seen in connection with tuberculosis of the vertebrae. The matter, consisting of caseous debris with pus-corpuscles and serous fluid, may travel considerable distances, forming, according to the place where it comes to the surface, the Lumbar, Psoas, or other abscess. The whole track of the abscess is liable to be infected by the tuberculosis so that there may be an extensive tubercular surface.

Healing of the tuberculosis occurs not infrequently. It may take place before any considerable extension of the process, the tissues overcoming the tubercular infection, and ultimately absorbing the necrosed products. But it also occurs after the process of softening and formation of abscesses. In that case when the tuberculous matter has been cleared out, healthy granulation tissue will be produced. This may produce new bone, so as to some extent to regenerate and replace that which has been lost. Where there has been much erosion or collapse, the new-formation will do little towards restoration, and will rather tend to fix the bones by Anchylosis in the position which they may have assumed. In Fig. 283 for example, the anterior parts of the bodies of the third and fourth cervical vertebrae have been destroyed and a piece of dense bone (at a) has been formed to act as a support. This has confirmed the acute curvature which is shown by the direction of the spinal canal. In Fig. 281 also, there has been a complete collapse of two bodies, whose spinous processes have coalesced (at b) while the bodies of the vertebrae above and below have also coalesced (at a).

Healed tuberculosis. The bodies collapsed anteriorly. Dense bone produced at a to form a support.

Fig. 283. - Healed tuberculosis. The bodies collapsed anteriorly. Dense bone produced at a to form a support. Permanent curvature and narrowing of spinal canal.

While healing may thus occur, the tubercular virus may still linger about the parts, and on the occurrence of a favourable opportunity it may renew" its advance. In the case from which Fig. 281 was taken, for example, the history showed what appeared to be a complete recovery (with curvature) three years before death, but a more recent onset ending in tubercular pleurisy led up to the fatal issue.

The tubercular process is accompanied by the ordinary phenomena of chronic inflammation, so that in the neighbourhood there is usually new-formation of bone, chiefly subperiosteal, and the surface of the bone may be rough with irregular projections.