The Cartilages Of The Joint And The Bones remain, in many cases, uninjured throughout the process: and excepting a perceptible turbidity, nothing unnatural is found in the synovia. In other cases, on the contrary, the cartilaginous coverings of the articular ends of the bones become diseased. Such cases are commonly looked upon as rheumatic affections of the joint; but chemical analyses of the original exudation, and of other secretions and excretions in the course of the disease, are required to establish their true nature. The cartilages become swollen, and thicker than natural, and usually uneven; they acquire a marked opacity, and dull white appearance, and gradually assume a fibrous texture. If the disease do not materially interfere with the use of the joint, the cartilages, when thus changed in their texture, and the menisci, or interarticular cartilages, are gradually worn away: and the exposed surfaces of the bones continually rubbing against one another, become dense and polished like ivory. The synovial membrane in such joints becomes still more turbid, of a dirty grayish color, and even flocculent. The progress of the disease is very slow, and frequently is quite unnoticed; indeed many observers have on that account been led to doubt its inflammatory nature.

In yet another class of cases the articular extremities of the bones are diseased; and they may be either primarily affected, or secondarily, by the advance of disease to them from the synovial membrane. I shall have occasion to describe these cases among the inflammations of the articular ends of the bones, as a change in joints probably dependent on gout.

Inflammations with a purulent, and those which have a sanious exudation, are on several accounts serious; because they frequently terminate in suppuration (phthisis) of the various tissues of the joint; because of the extension of suppuration beyond them; because of the so-called spontaneous dislocations of the bones which ensue; and, lastly, because of the anchylosis in which they terminate in favorable cases.

The quantity of purulent fluid effused into the cavity of the joint is generally considerable, and the capsule is consequently much enlarged: the synovial membrane is lined with a firm, shreddy layer of lymph, which is dissolving into pus, and a softer purulent precipitate, which can be easily removed, adheres to the cartilages. The first-mentioned layer is opaque and lustreless, its surface is rough, and serum is infiltrated, and blood in small spots extravasated through its tissue, as well as through that of the fibrous capsule of the joint, and neighboring cellular structures. As the disease advances, the infiltration and thickening of the neighboring structures increase, they become filled with a gelatinous, lardaceous, white product, in the midst of which fibrous tissues, capsule, ligaments, or aponeuroses, can no longer be recognized. Here and there, in the mass, there are cavities of different dimensions, the lining of which is vascular, spongy, and granulating, and the contents purulent. The muscles near the joint are pale and flabby, infiltered and attenuated. At length the infiltration reaches the subcutaneous cellular and adipose tissues, and the integuments become fixed to the disorganized structures beneath. The diseased joint then presents the following external appearance: it is swollen, and always more or less bent; it feels everywhere soft and flabby, or in some spots flabby, in others firm, elastic, doughy, and, at the same time, tuberculated; the integuments over it are tense and pallid, - leucophlegmatic, or they are traversed by varicose veins. (White swelling. Fungus articuli).

At length ulceration commences, and advances in various directions. Externally, the capsule ulcerates in one or more spots, and then the soft parts adjoining it. In some instances, large openings form in the capsule, and connect the joint with ulcerated cavities in the soft parts; in others, mere sinuses are formed: but in either case they open externally through the skin, and occasion and maintain a discharge of the contents of the joint. Internally, the interarticular cartilages and the ligaments ulcerate, the cartilage covering the bones, when brought into contact with the matter, is destroyed in the way that has been mentioned, and the ulcerative inflammation attacks even the bones, if they have not been involved already.

The cavity of the joint appears like a cloaca, surrounded with a gela-tino-lardaceous mass: the integuments covering it are of a dark-red hue and are especially discolored at the orifice of the sinuses. The joint contains pus or sanies of an offensive odor, and variously discolored, the repeated hemorrhages which take place when there is acute caries of the bones, very frequently giving it a red or brown tinge: the ligaments ulcerate, and the cartilages separate, partly or entirely, from the bones: the osseous surfaces are laid bare, their compact wall is destroyed, and the spongy tissue is exposed, infiltered with pus and ulcerating, and surrounded on all sides by osteophytes of various shapes; remains of the fibrous structures of the joint, pieces of loosened cartilage, and of necrosed bone, are mixed with the matter discharged from the joint. The soft parts, and the entire bones belonging to the diseased joint are wasted, most of the fat is absorbed, the muscles are remarkably blanched and thin, and the bones, being generally in a state of excentric atrophy, are soft and fragile.

More or less quickly after the disease has reached this stage, spontaneous dislocations, as they are called, ensue. In modern times doubt has been cast upon the fact of dislocation occurring in consequence of large effusion into a joint, but experience certainly proves that such dislocations do take place. The head of the femur has, in some few cases, been forced out of the acetabulum by a large exudation into the hip-joint; and thus the views of ancient authors on the subject of Coxarthrocace, though, in many respects, unquestionably defective, are justified, and the manifold criticisms to which they have been subjected, are corrected.

The greater majority of these luxations occur in the last-described stage of an inflammation attended with purulent exudation, and are consequences of the destruction of the ligaments and articular ends of the bones; they are brought about by the continued action, and follow chiefly the direction, of the flexor muscles; though if the bone be much destroyed towards any other part, the direction of the dislocation will be modified accordingly.

The most favorable case of repair of this disease, is discharge of the matter, and anchylosis of the joint. The cavity of the articulation is obliterated, being filled with a new growth of organized cellular tissue, and with an abundance of fat. The bones become knit together, either by means of an ossifying exudation, which is furnished by their compact articular surface, or, if caries have taken place, by the granulations which spring from their exposed spongy tissue; and the more closely the bones are in contact, the earlier is the union completed. The soft parts around, which have been inflamed, infiltrated and ulcerated, contract, assume a white fibroid texture, and cicatrize; and the whole joint appears wasted.

Inflammations, which furnish a hemorrhagic product, take place under the general and local conditions which are peculiar to them: they chiefly attack large joints, and especially the synovial membrane of the knee. They are usually associated with hemorrhagic effusions into large serous sacs.

In those inflammations, the product of which becomes converted into tubercle, the same conditions may be observed, which have been adduced as applying to inflammations of this kind in serous membranes in general; they constitute the usual, and almost the only form in which tuberculosis occurs in synovial membranes. They lead to tubercular ulceration and destruction of the tissues of the joint, and are the cause of a great number of what are called "white swellings." I shall have to advert to this subject again.