TUBERCULOSIS OF THE BONES tSee Schlossmann, Tuberculosis, vol. ii.) Etiology and Pathology.—Infection is usually carried by the blood cu•rent as in pytemic affections. The primary seat of infection is not the marrow but the osseous tissue and the fine terminal arteries near the epiphysis, where of bacteria are held up and begin their work of destruction. The fine branches in the zone of growth explain why this is the most favored site for this form of infection in the long bones. In the small bones the artery divides at once into numerous small branches so that foci may be very generally established (Lexer).
Tuberculosis of the bones is always secondary to a primary focus which may quite often be far away (bronchial glands, bronchial mucosa, etc.).
An injury may be the exciting cause, as it lowers the vitality of the tissues to such an extent that an invading infection cannot be resisted as in full health.
The disease progresses through blocking the arteries and the spread of the nodules in the poorly nourished regions. The masses of granu lations dissolve the bone and bone cavities are formed which are filled with cheesy pus (caries) (Fig. 119, Plate 11). In some cases part of a bone will die from lack of nourishment and will become separated from the healthy tissue as a sequestrum and will be found lying in a bone cavity surrounded by pus and granulations (necrosis). In the epiphyses the foci are usually wedge-shaped, corresponding to the course of the branches of the blood-vessels..
In the meantime the tissue shows a reaction by attempting to wall off the disease and to form an involucrum. Periosteal excrescences must be regarded as reparative processes, which will form swellings especially on the small long bones.
While we find wedge-shaped foci near the epiphyses of the large tubular hones (Fig. Plate 11), the arrangement of the blood-vessels in the short bones will favor a more profuse process which will destroy the bone from within and at the same time regenerative processes will take place in the periosteum with the formation of new bone tissue (spina ventosa) (Fig. 117, Plate 11).
Differences occur according to the situation and nature of the affected tissue. When near a joint there will always be danger of the disease invading it (tuberculous osteoarthritis).
The pus is thin and contains detritus (bone sand). It contains very few bacteria and only very few cellular elements. It spreads into the neighboring tissues when the exudative pressure increases and follows the line of least resistance (gravitation abscess).
The symptoms of tuberculosis of the bones are most insidious. It frequently begins without any pain (spina ventosa), and only when the joint or the movable parts in and around the joint are attacked will pain arise. Tuberculous abscesses grow slowly, without much fever and with few local or general disturbances.
The diagnosis of tuberculosis of the bones is easy per se, but the diversity of the picture in the different bones may make it difficult. The swelling of the small tubular bones has been known for a long time as "spina ventosa," and the process appears similar in the cuboid bones of the carpus and tarsus in which the inside of the bone is destroyed, though without much periosteal thickening (see Spondylitis). On the flat bones we observe multiple eroded foci which are surrounded by a low bony wall (Plate 11).
When abscesses form they grow slowly without any symptoms of reaction; the sites of perforation form ulcers with gray flaccid borders; the poorly nourished and disintegrating granulations, which represent the feeble and ineffective resistance of the body, protrude everywhere. The pus is usually sterile, but when we rub down the granulations or centrifuge the pus we will find the tubercle bacilli. Intraperitoneal injection of the masses in a guinea-pig proves the diagnosis through the death of the animal from tubercular peritonitis.
In the long bones we may have difficulty in differentiating the disease from osteomyelitis, especially when we meet one of those rare cases of either tuberculosis of the diaphysis or of epiphyseal osteomye litis, and also when we have a case of the slow subacute type of osteo myelitis.