These diseases commence either in the fibro-serous capsules, or in the bones, and scarcely ever in the cartilaginous coverings of the ends of the bones or in the interarticular cartilages. In the course of disease, however, all the different textures composing the joint are affected, and in different ways: this remark applies especially to inflammation, which is by far the most frequent disease of joints. In treating of it, therefore, as well as of the other diseases of texture to which reference must be made, I shall observe that distinction in a manner as closely accordant with nature as possible.

1. Inflammations. A. Inflammation Of The Synovial Membranes Of Joints

In the consideration of this, as well as of the other diseases of synovial membranes, frequent reference must be made to the statements contained in the chapter on the Diseases of Serous Membranes in general (p. 27).

Inflammation of a synovial capsule is sometimes a primary disease, and occasioned either by various injuries, such as fracture within or near the capsule, dislocation, etc, or by atmospheric influences; in the latter case it is named rheumatic: sometimes it is secondary, and results from metastasis. It is also very frequently brought on by the inflammation of an adjoining tissue, as of the bones, or their articular extremities, or by caries, necrosis, etc, in the neighborhood of the joint.

Secondary inflammations - those which are the result of metastasis - occur chiefly in the larger joints, and especially in the knee.

Moreover, the inflammation may have an acute course, or may be chronic. In either case, it may produce any of the different exudatioins mentioned in the chapter that has been cited, and may have in general the same terminations. The best-marked inflammations in the structure under consideration are those which furnish a purulent or a hemorrhagic exudation, and those the product of which becomes converted into tubercle. When the amount of exudation, and the consequent enlargement of the synovial membrane, are considerable, and when the disease involves, on the one hand, the cellular, muscular, and fibrous soft parts, and the ends of the bones on the other, the whole disease constitutes that affection which, from certain stages of its progress or from some one prominent character, is commonly called white swelling (fungus articulorum, spontaneous luxation, Arthrocace). A case of this kind is most marked when the inflammation produces a purulent exudation, and terminates in suppurative destruction of the tissues of the joint, and when the exudation is tuberculous. Commencing originally in the synovial membrane or in the articular ends of the bones, this affection generally, when it is far advanced, involves such various textures, and produces such degeneration and destruction of them, that it costs some trouble to determine its original seat. And it is further important to remark, that whilst it is not altogether uncommon for it to commence in the articular ends of the bones, yet the synovial membrane is far more commonly the organ first diseased. The inflammation of that membrane very often occurs in several joints at the same time; and with chronic inflammations of the larger synovial membranes, there frequently coexist inflammations of the same character, so far as the products are concerned, in large serous sacs, such as the pleura, the pericardium, etc.

A second, and yet more important observation is, that no exudation is deposited on that portion of the synovial membrane which covers the cartilages; if any of it should adhere to that portion of the membrane, it is in no case, whatever form it assume, to be regarded as a primary peripheral plastic effusion, but as a secondary precipitate, or deposition out of the general exudation in the articular cavity; and the opacity of the cartilages and of the layer of synovial membrane covering them is the result of imbibition.

Slight Acute Inflammations

Slight Acute Inflammations produce rather a turbid exudation, which is for the most part serous, and is easily reabsorbed. They terminate in resolution.

If the product of the inflammation consist of an effusion of serum and of a larger quantity of plastic material, the synovial membrane loses its glistening aspect, becomes opaque and more or less swollen, and is covered on its inner surface with a peripheral plastic effusion, which varies in thickness, and in the character of its free surface. Sometimes it constitutes a thin layer, sometimes a thick one, of uniform or of unequal depth: and as in the latter case there are some extensive spots on which it is scarcely perceptible, and other smaller ones, on the contrary, at which it is accumulated, it forms islands or "plaques" of various, and sometimes very considerable thickness, or even nodulated masses. When it is of trifling thickness, its free surface usually appears fine and villous, but when its thickness is considerable, the surface is shreddy. Very frequently also there is found cleaving to the surface more or less of a soft precipitate out of the effusion, which can be easily removed.

As the whole process is usually chronic from the first, or becomes so in its course, the effusion which remains, and* the enlargement of the capsule, render any adhesion and union of the surfaces very rare; and the plastic effusions are converted into a new tissue, composed of free or of coarse shreds, and of fibrous (fibroid, fibro-cellular) texture, which adheres to the synovial membrane.

Specimens are to be met with in nearly every collection, of large joints (especially knee-joints) in which the capsule is enlarged and thickened, and its inner surface covered with white shreds of various lengths, which are occasionally so numerous, that the joint seems as if it were lined with felt; sometimes the shreds are simple, smooth, rounded, or rather flattened threads, or they here and there form a membranous patch upon the surface, or have their free extremities split into filaments and resembling a tassel. In extreme cases, small, smooth, and subovate bodies, which Mayo compares to melon-seeds, are attached to their extremities, hanging singly or in clusters from each stalk: and lastly, here and there amongst them shapeless masses are attached by broader bases. They all have a fibrous or fibroid texture, and are of innocent character, having nothing in common with the cystic and cancerous productions which are found on normal or anomalous serous membranes.