becomes perforated when the new growth spreads to the neighboring parts (Fig. 58). In all forms of sarcoma there is absorption of the bone-substance in the vicinity. A form of sarcoma springing from the periosteum is described under the name of osteoid sarcoma. This tumor consists of fibromatous or round-celled sarcomatous tissue in which osteoid elements are irregularly embedded. More or less calcification and bone-formation are observed. The tumor may be quite soft or very hard; it tends to spread to the neighboring soft parts, and may give rise to metastasis. It is particularly frequent at the ends of the long bones.

Secondary sarcoma of the bone-marrow is not rare in general sarcomatosis.

Myeloma. This term has been applied to a form of multiple primary tumor of the bone-marrow allied to the lymphatic growths of leukemia and Hodgkin's disease. The term lymphadenia ossea has also been given to it. Probably a number of distinct conditions (some of them secondary tumors) have been described under these names.

Chloroma is a form of sarcoina, having a greenish or yellowish color, that is met with in the periosteum, especially about the orbits and other parts of the skull.

Primary carcinoma of the bones has been observed in a few cases. It can only be explained upon the assumption that islets of epithelial tissue have been deposited in the bone by faulty development. Most cases, however, described as primary carcinoma were probably in reality alveolar sarcomata.

Secondary carcinoma of the bones is not rarely met with, especially in cases of cancer of the breast, thyroid gland, and prostate. The secondary nodules may occupy the periosteum or the bone-marrow. The bone becomes exceedingly fragile, and fractures are not infrequent.

Cysts and Parasites.-Cystic transformation of myxomata and of sarcomata may be met with. Occasionally dermoid cysts are observed. Among the parasitic diseases Cysticercus cellulosa has been described in a number of instances.

CHAPTER X.

DISEASES OF THE JOINTS.

Luxation. The most frequent injury of joints is that known as luxation, in which the relations of articulating bones are disturbed. In these cases the ligaments and other soft tissues around the joints are more or less torn, and in consequence become inflamed. If the luxation is reduced, this inflammation subsides quickly, and frequently normal conditions are restored. If the luxation persists, various secondary changes may occur. Ankvlosis in abnormal positions may take place by the formation of fibrous adhesions, or in more favorable cases a false joint may be established. In the latter cases local atrophy takes place in one of the bones, forming a depression into which the end of the other fits. Later, ossifying periostitis produces an elevation around the depression of the socket, and thus a well-formed joint may be produced.

Ankylosis is the term applied to the condition in which the normal movability between articulating bones is prevented by interosseous attachments. Pathologically, ankylosis may be fibrous, cartilaginous, or bony. All of these forms are met with after chronic inflammatory conditions of the joints.

DISTORTIONS OF JOINTS.

Distorted conditions of the joints may be due to contractions of the muscles and tendons, or to cicatricial tissue in the neighborhood of the articulation. Changes in the joints themselves may be present as primary or as secondary conditions. Among the more important of such deformities of joints are the various sorts of club-foot: pes varus, the sole of the foot turned in; pes valgus, the sole of the foot turned out; pes equinus, the foot extended and supported upon the anterior ends of the metatarsal bones; pes calcaneus, the foot flexed and resting on the heel. Combinations of these conditions are frequently met with. At the knee-joint are found: genu valgum, in which the knees are bent in (knock-knee), and genu varum, in which the knees are bent out (bow-legs).

CIRCULATORY DISTURBANCES.

Hyperemia of the joints occurs as a part of acute inflammations, and involves the synovial membranes particularly. The synovial fluid may be increased in quantity.

Hemorrhage into the joint may result from traumatic causes or from inflammatory conditions, particularly in the course of hem

orrhagic diseases, notably scurvy and hemophilia. The blood may remain fluid for a long time, and the joint not rarely has the appearance of chronic arthritis with effusion. Later, resorption of the blood takes place.

Dropsy of the joints occurs in the course of acute and chronic inflammations.

INFLAMMATIONS.

Acute arthritis may be traumatic or hematogenous, or in other cases is secondary to disease in the vicinity. Hematogenous arthritis may occur in the course of various infectious diseases, such as scarlet fever, small-pox, pyemia, etc. In the same group must be considered acute articular rheumatism, which is doubtless an infection conveyed to the joint through the blood.

Pathologic Anatomy.-Various forms may be distinguished, such as the dry or fibrinous, the serous, and the seropurulent. In all cases there is, first, a deep congestion of the synovial membrane. The ligaments and the cartilage are more or less implicated at the same time. The terms synovitis, implying involvement of the synovial membrane, and panarthritis, implying general involvement, may be applied. In the dry or fibrinous form there is a deposit of fibrin upon the surface, with or without serous exudation. In the genuine serous form the exudation is purely serous, but more commonly seropurulent liquid is observed. Entirely purulent exudate is sometimes formed (empyema of the joints).

Results. In the milder cases complete resolution may take place without destruction of the tissues of the joint. In the more serious cases there is inflammation of the articulating cartilages, with consequent ulceration or caries, or even considerable necrosis, of the cartilage. The underlying bone may be laid bare, and ostitis or osteomyelitis may result. Sometimes discharge of purulent material into the surrounding tissues occurs, and fistulous communications with the exterior may be established. These processes may lead to extensive disorganization of the joints, with luxations and, in later stages, ankylosis.

Associated Conditions.-General systemic infection may follow these acute inflammations of the joints.

It

Chronic arthritis may be due to a variety of causes. may follow the acute forms already described or may be primarily chronic. Among the more important causes are traumatism and certain infections. It occurs in the course of gout and in certain nervous diseases, probably as the result of disturbance of the trophic mechanism. Chronic arthritis of the aged has perhaps a similar causation, and rheumatoid arthritis is nearly allied.

Pathologic Anatomy.-A variety of forms may be distinguished. The same etiologic factors may, however, give rise to one or another in individual cases.

Chronic serous arthritis, or hydrops articulorum, is frequently due to repeated acute arthritis. The joint is filled with thin synovia, and the synovial membrane is somewhat thickened. The surface of the joint may be more or less covered with an injected synovial membrane (synovitis pannosa). The knee-joint is most frequently involved.

Chronic purulent arthritis is always infectious, and is usually the outcome of an acute seropurulent or purulent arthritis. The

conditions met with have already been described. It terminates in more or less extensive disorganization of the joint, and in favorable cases in fibrous ankylosis (Fig. 341).

Arthritis deformans, or rheumatoid arthritis, occurs in persons past middle age, but sometimes in young persons, and even in childhood. Constitutional depression and exposure seem in some way to predispose. There are, first, alterations in the cartilages of the joints, consisting of softening and ulceration or erosion, which make the surface irregular and rough. At the same time some hyperplasia of the cartilagecells takes place, but the hyperplas tic elements subsequently undergo degeneration, and are absorbed. In this way the cartilage is gradually FIG. 341.-Fibrous ankylosis, due to reduced and the ends of the bone laid bare. The synovial membrane and ligaments at the same time become thickened by hyperplasia. Subsequently the articulating end of the bone is involved. There is, first, absorption, and secondarily proliferative changes at the periphery of the articulation, in the form of exostoses or osteophytes. The joint is considerably deformed and thickened. Subluxations are common, and the deformity leads to immobility of the joint, or ankylosis. This form of arthritis is particularly common in the metacarpo-phalangeal joints of the hand, and in the other small joints of the hands and feet (Fig. 342). Later the knee, elbow, and vertebral articulations may be involved.

chronic purulent arthritis.

Chronic dry arthritis with ulceration, or senile arthritis, is particularly common in the hip-joint (malum coxæ senile). There is gradual absorption of the cartilages and of the exposed surfaces of the bone. Subsequently the surrounding parts of the bone undergo sclerosis and hypoplasia. The changes are similar to those of rheumatoid arthritis, but are more slowly developed.