The principal disease to which cartilage is liable is-

1. Inflammation, a subject of much discussion, on which its anatomical characters and experiment have been alike brought to bear.

From our present knowledge of the texture of cartilage, as well as from direct observation, we are compelled to deny, that true cartilage, while its texture is normal, ever inflames; but we know by experience that, without being the immediate seat of an inflammatory process, such a cartilage may suffer very serious, and sometimes very rapid, lesions of its texture, from the effect produced on it by inflammation of adjoining tissues, and by the products of that inflammation, and even from imperceptible anomalies in the composition of the synovial fluid. No doubt it is this sensitiveness of cartilaginous tissue to the influence of neighboring inflammation, and inflammatory products, which has led to the presumption, that cartilage does itself inflame; and such a presumption would seem confirmed, if the adjoining inflammation were regarded as secondary to that of the cartilage. The structures which inflame in such close contact and relation with cartilages, and on which the changes in the cartilages now under consideration may in some measure be studied, are the synovial membranes of large joints, the articular ends of bones and perichondrium. The last-mentioned structure may be the seat of a primary inflammation, or may become involved in inflammation or ulceration going on in other tissues, such as mucous and serous membranes, muscles, etc. The vascularity which Mayo and Liston have observed in cartilages during their absorption, and to which I have also referred at p. 212, is without doubt a subordinate occurrence, coming on when the texture of the cartilage is already diseased. When it is in this secondary condition, it may of course become the seat of inflammation, and a free product, consequently, may be found exuded on the surface of parts at which absorption is going on.

In cases of slight inflammation of synovial membrane, and even in those in which, from old age, or from the joint having been unused for some time, the synovial fluid has diminished in quantity, and at the same time probably undergone some change in its constituent elements, the articular cartilages lose the lustre of their surface, without becoming reddened, or perceptibly injected. As they continue longer in contact with the exudation, they assume a yellow color, and a looser and softer texture than natural, so that they look like short-napped felt. On minute examination, the intercellular substance is found at first to be rendered opaque by the presence of a number of fine points and indistinct filaments: afterwards the filamentous arrangement becomes more distinct, and is found to be produced sometimes by fibrils of wavy cellular tissue, and flattened fibres, which are degenerating and assuming a similar character, - both which, as well as the rest of the intercellular substance, swell, and become transparent, when treated with acetic acid, - and sometimes by delicate, nucleated fibres spread out into a membrane.

The cells are round, as if distended, and project from the fibred blastema; in many of them the nucleus is indistinct, and breaks into small rounded points, or degenerates into a fat-globule: in the latter case there is a good deal of free fat in the blastema, and the cells are filled with small shining molecules of fat. When in this state, just as in atrophy, the cartilage is gradually worn down and lost.

When the cavity of a joint is filled with purulent exudation from the synovial membrane, the most superficial layer of the cartilages, being in contact with the matter, loses its glistening and translucid character, and becomes of a dirty yellowish color; but as it gradually changes into a gelatinous substance, it becomes transparent, though it still remains discolored. The proper texture of this layer is completely destroyed, and it degenerates into a finely granular mass. The changes already described go on in the subjacent layer; that is to say, the intercellular substance assumes a fibrous character, and fat is developed in remarkable abundance. When the costal cartilages suppurate in this manner, groups and bundles of peculiar, stiff, straight fibres are sometimes formed in the intercellular substance.

These changes are sometimes found occupying the whole surface of the articular cartilages uniformly, but more commonly they are confined to certain spots of various sizes.

If the articular ends of the bones be acutely inflamed, some of the product of the inflammation which is effused upon their surface loosens the cartilage from them; and in that case the change above described takes place in the cartilage, so soon as the inflammation has extended to the synovial membrane, if it have not done so already.

The same changes in cartilage ensue when its perichondrium is inflamed, and the purulent matter is effused on the inner surface of that membrane: of this we have an instance in inflammation of the investing membrane of the cartilages of the larynx. They suffer in the same manner if the perichondrium be destroyed by ulceration advancing from other organs; as is the case in the cartilages of the larynx when situated at the base of degenerated typhous, or tubercular ulcers; or in the cartilages of the ribs, when there is any tuberculous ulceration of the costal pleura.

It is an old and interesting observation, that ossification is apt to be induced in cartilages by the occurrence of inflammation in their vicinity; but it takes place only in those cartilages which by their physiological constitution are wont to ossify, such as the cartilages of the ribs and larynx.

Inflammation

Inflammation, though rarely met with in the fibro-cartilages, does unquestionably occur in them; but the changes it produces in them differ somewhat from those just described. It is remarkable for its acute course, and for the rapid ulcerative destruction of the fibro-cartilage to which it leads: its anatomical characters are much the same as those of inflammation of fibrous organs. An inflammation is sometimes met with in the intervertebral cartilages, which terminates sooner or later in suppuration, and is generally in the end combined with inflammation and caries of the bodies of the vertebrae, inflammation of the spinal membranes, etc.

After difficult parturition, the synchondroses of the pelvis, and especially the fibro-cartilage of the symphysis pubis, are subject to an in-flammation of low type, which owes its origin to putrefactive (septic) phlebitis, and rapidly destroys the fibro-cartilage in a similar manner to the worst forms of putrefaction. (Compare p. 55.) The cartilage is found enclosed in a capsule formed of the adjoining ligamentous apparatus, but it is changed into a diffluent, fetid pulp, resembling chocolate or coffee-grounds, or into a fluid sanies. Sometimes the disorganized mass is found in an irregular cavity, having insinuated itself to various distances beneath the periosteum of the neighboring bone.

In the cartilages which Miescher has named the yellow cartilages, and which have a general connection with those now under consideration, an inflammation occurs, which is mostly chronic in its course, and which, after loosening and swelling the texture of the cartilage, usually terminates in atrophy and fibroid induration of it, and consequently in deformities of various kinds. Hence the epiglottis, and more frequently some of these structures about the tarsus, are found puckered, bent, tilted upward or downward, etc.

2. Ossification Of Cartilage

Some of the true cartilages are, under various circumstances, subject to real ossification, to conversion into genuine bone. The thyroid and cricoid cartilages ossify in this manner in men at about forty years of age: and ossification of the costal cartilages is so frequently observed in old persons that it can only be looked upon as a pathological appearance when it is found at an earlier period of life. The cartilages of the larynx ossify from different points: those of the ribs change to a dirty yellow color in old age, become saturated with fat, and then ossify in the middle, the central vascular canal enlarging so as to form a medullary cavity. The ossification of those laryngeal cartilages which I have mentioned, is often excited and advanced by inflammations which extend to the perichondrium from without, especially the inflammation which occurs at the base of tubercular ulcers and in the neighborhood of softening tubercle. Hence it sometimes happens that tracheal phthisis is after a time complicated with caries of the newly formed bone.

True ossification of a fibro-cartilage is in every case highly problematical. The anchylosis of synchondrosis which appears to result from such a change in the fibro-cartilage, is probably never produced by conversion of that structure into bone. Either new bone, in the form of an osteophyte, passes between the margins of the adjacent surfaces of the anchylosed bones, enclosing the fibro-cartilage in a sort of capsule: or the two bones are united together in the whole extent of their adjoining surfaces: in the latter case, there can be no doubt that the new osseous matter is formed on the surfaces of the old bone, while the fibro-cartilage is absorbed. In this class of cases are included those rare ones of complete anchylosis of the synchondroses of the pelvis and of the vertebral bodies; and allied to it is another kind, in which the vertebrae are fused together on the concavity of lateral curvatures in consequence of the absorption and displacement of the intervening cartilages by pressure.

On the other hand, several of the so-called yellow cartilages are in very rare cases seat of a bony concretion, which is formed in some fibroid callus left in them after chronic inflammation. The epiglottis is an instance of this.

3. Adventitious Growths

These growths appear not to occur in the cartilaginous system, and certainly they do not in true cartilage. Its structure will resist the progress of advancing cancer for a long time, and even altogether. The costal cartilages do indeed disappear in the degeneration of large mammary cancers, and the arytaenoid cartilages form a very remarkable exception to the rule; for from what I have hitherto been able to ascertain, it appears as if the cancerous growths, or those suspected to be cancerous, which project into the larynx, very commonly spring from those cartilages. Tuberculous and cancerous degenerations affect the cartilages in the manner already described under the head of Inflammation.