MORBID ANATOMY - ARTHRITIS DEFORMANS.
Seeing that the changes in the articular structures which result from arthritis deformans have been carefully studied by a long series of able observers, our knowledge of these changes, at any rate in their more advanced stages, is tolerably complete. All the tissues which enter into the structure of the joints, viz., cartilage, bone, and synovial membrane, share in the morbid process, but it cannot even yet be stated with certainty which of these structures is first attacked, al though there is a great probability that the cartilaginous coverings of the articular ends of the bones tire the actual primary seats of the disease.
.This uncertainty is not a matter for surprise if it be remembered that arthritis deformans is not in itself a fatal malady; and conse quently that it is only very occasionally and, so to speak, acciden tally that an opportunity is afforded of examining the joints in the earliest stages of the disease.
It cannot be contended that the observed changes are absolutely characteristic of the cases to which the name of arthritis deformans is usually applied, for similar lesions are met with in the joint disease of locomotor ataxia, in that which occurs in haemophilia, as well as in gouty cases of long standing. Even among the cases commonly classed together as examples of arthritis deformans there exist con spicuous clinical differences, such as separate the hip-joint disease of elderly men from the more acute affection of many joints which is unfortunately so common among women ; sometimes again it seems that arthritis deformans developing late in life and running a very slow course is little more than a senile change in the joints.
In describing the morbid anatomy of the disease under considera tion it will be well to consider the changes in the several articular structures separately, and to describe in turn the fibrillation and ero sion of the cartilages ; the eburnation and abrasion of the bones, and the outgrowths of new bone around the articular surface ; and lastly the hypertrophy of the synovial fringes and other lesions of the synovial membrane.
The cartilage lesions are among the most characteristic of the morbid changes of arthritis deformans. In the early stages of the disease the articular cartilages of the affected joints are seen to have lost their uniform structure, and to present the appearance of velvet; the "nap" consisting of delicate fibrilhe formed from the ground substance of the cartilage, from which the cellular elements have dis appeared.
The manner in which the fibrillation is brought about has been carefully studied by Conan and Ranvier," from whose description the following account is condensed. The earliest morbid appearance observed is the multiplication of the cells throughout the entire thick ness of the cartilage, and the formation of capsules around some of them. Within these primary capsules a number of secondary cap sules are formed, which may be either independent of each other or grouped together in common envelopes. Previous observers had mistaken these capsules for true cartilage cells, but Coruil and Ran vier showed that this is not their real nature by staining them with iodine, which colors the protoplasm of the cartilage cells brown, but barely imparts a tint to, or altogether fails to stain, these secondary capsules.
The next event is that those primitive capsules which approach most nearly to the surface rupture into the articular cavity, and those which are more deeply seated, being able to grow only toward the surface of the cartilage, rupture into each other, and in this way a series of parallel tubules is formed, and the ground substance of the cartilage is split up into filaments.
The velvety cartilage is before long completely destroyed in places by the friction of the articular surfaces upon each other, leaving the underlying bone completely bare. As might be expected, the removal of the cartilage is first brought about over the central portions of the articular surfaces, but as time goes on the exposed area becomes more and more extensive. As was originally pointed out by Sir James Paget, the remarkable tendency to symmetrical invasion which is so characteristic of arthritis deformans is manifested even in this, and the destroyed area in the joint of one limb may closely corre spond both in shape and in position with that in the corresponding joint of the opposite limb. Rindfleisch holds that the destruction of the cartilage is not purely mechanical, but is greatly facilitated by the process of mucous degeneration, and it is interesting to note, in this connection, that Hoppe-Seyler" detected the presence of a large amount of mucin in the synovial fluid removed from a diseased joint.