Inflammation, and the inflammatory osteoporoses or rarefactions, of bone having been already considered, there are only a few special remarks to be made in this place.

The articular ends of bones are frequently the seat of inflammation, especially in young persons; and the inflammation often passes into caries. Inflammation of the synovial membrane, of course, accompanies it, with equal readiness and frequency; and there is great difficulty in any particular case of inflammatory disease, especially in one of ulcerative destruction of a joint, to determine in which structure the disease originated.

As a general rule, that structure was the first diseased, in which the inflammation and destructive process are most advanced. If there be a considerable production of new osseous substance (osteophyte) around the articular ends of the bones, and on those portions of their articulating surface which have been divested of cartilage, if the ends of the bones be much enlarged, and their tissue expanded, if they be extensively carious, if matter be formed in their interior, but especially if the cartilage covering them be loosened, and the epiphyses separated, it is highly probable that the original disease was in the bones. The inflammation of the bones not unfrequently leads to an exudation which bears the characters of tubercular matter, - to a tubercular infiltration, in fact, of the spongy tissue of the bone; when this occurs, it is usually under the influence of a deep tuberculous taint of the system, which has, moreover, already exhibited itself by a tubercular deposition in some other part. Inflammation of the synovial membrane, attended with an exudation of tubercular matter, generally soon follows. (Vide Tuberculosis of Joints, infra.) The disease next in order is that form of Osteoporosis of the articular ends of bones, which I have, at pagel39, distinguished as inflammatory; it ends in a particular kind of induration of the osseous tissue, and produces peculiar deformities of the bony apparatus of joints. An attempt to delineate it was made (p. 159) in the chapter on the characteristic features of Constitutional Affections of Bone, where it was represented as a change very probably dependent on gout.

The disease of the joint commences with loosening or expansion of the tissue of the bones and enlargement of their articular ends, and it evidently is chiefly confined to the prominences or articular heads. This softening and swelling of themselves occasion various deformities of the bony structures of the joint, and they are usually rendered still more striking by exuberant growths, which spring up simultaneously around the articulating surfaces. The most common deformity is that in which articular prominences become flattened, and their margin overhangs to such an extent, that their whole form resembles that of a mushroom: a corresponding widening and flattening take place in articular fossae. But an articular prominence, especially the head of the femur, may be deformed in another way: it may maintain its shape, but still have an overhanging border; or it may be flattened from above only, and, at the same time, depressed; and may have a groove or impression at its upper circumference: in other cases it is elongated and conical; in others, again, uneven and tuberculated. Corresponding to each of these deformities of articular prominences, there is a deformity of the fossae which they occupy. The expansion of the bony tissue (the osteoporosis) gradually passes into a white chalky condensation, or sclerosis.

The cartilages of the joint are gradually removed, and their removal is effected by several means. In the first place, their texture is probably altered by an exudation, which is poured out during the process of rarefaction upon the articulating surface of the bone. As the exudation thoroughly saturates the cartilages, their blastema assumes, as has been remarked, a fibrous structure, and they become of a dull white color, and, at the same time, softer and more moist. This change of texture occurs the sooner if the disease in the bone be accompanied by inflammation of the synovial membrane, and effusion into the cavity of the joint. Whilst the cartilages are thus prepared for removal, the condensation of the bone, and the rubbing of the altered cartilages themselves against each other, effect it. The one impedes or prevents their nutrition by the vascular apparatus of the spongy tissue of the bone, the other wears them down; and does so with a rapidity proportioned to the loss of elasticity and of resisting power, which the change in their texture has occasioned.

When the cartilaginous coverings are removed, the continued attrition gives the condensed articular ends of the bones a polish like that of gypsum. At the same time, the interarticular cartilages, which have become useless from the deformity of the articulating surfaces, and have suffered more or less compression, are also worn down and removed. And in the hip-joint, the ligamentum teres always disappears, partly because it is wasted in consequence of the induration of the bone, and partly by being worn away.

The inflammatory process extends from the bones to the synovial membrane. The capsule is almost always thickened; internally it is frequently found of a rusty brown or slate-gray color, and lined with a false membrane, that has a delicate villous surface, or with the fibroid growths before mentioned. The fluid in the joint is thin, turbid, and of a dirty grayish color. Moreover, the capsule of the joint is dilated in proportion as the articular fossae are enlarged; and its insertions extend beyond the normal bounds of the joint.

For other anomalies of the same kind, as well as for the enumeration of the joints most frequently affected with them, reference maybe made to what has been said at other parts of this work; there is but one remark to be added here, which is, that the disease not unfrequently occurs symmetrically in corresponding joints.