Concerning the mode of formation of these substances considerable differences of opinion have prevailed, which may justify a slight notice in this place.
The descriptions of Cruveilhier, Hyrtl, and others, leave no doubt as to what is the pro cess of their development in at least a large proportion of instances. These exhibit them as affections of the subserous, or rather sub synovial areolar tissue ; while the circum stances under which they are found, such as the arrangement of the deposit in small masses, which are plentifully scattered over a large surface, the aged and debilitated constitutions in which they are chiefly present, &e., indicate with tolerable clearness that they are the result of disease, as contraclistinguished from external violence.
But it may be doubted whether this expla nation will apply to these unattached bodies universally : it seems more probable that amongst these substances are included some which have not only a different origin, but also a different relation to the synovial mem branes.
Thus, it was imagined by Hunter* that " the loose cartilages usually found in the knee-joint originated from a deposit of coagu lated blood upon the end of one of the bones, which had acquired the nature of cartilage, and had afterwards been separated." He conjectured that their pedunculated shape during the period of their attachment de pended on the movements to which such deposits were liable during their soft con dition ; and in confirmation of this he adduces an instance in which some blood effused in the abdominal cavity acquired a peduncle half an inch in length before it lost its red colour, and, when washed, exactly resembled a pendulous tumor. And as to the possibility of the transformation of such an effusion into a cartilaginous-looking substance, reference is made to an examination of joints which had been violently strained or otherwise injured, where the patients had died at diffe rent periods after the accident. In some of these there were small projecting parts, pre ternaturally formed, as hard as cartilage, and so situated as to be readily knocked off by any sudden or violent motion of the joint." The frequent connection of this variety of loose cartilage with external violence has long been known, and in some Of these cases symptoms of local inflammation mark the period of their formation ; while, after a cer tain interval, the accident of their separation occurs, attended by the ordinary effects on -the movements of the joint.
These facts, however, while they afford a great probability that external violence may operate as a cause of these growths, by giving rise to an effusion, which in some instances consists, it is most likely, of blood ; yet they do not exhibit the relation of this effusion to the synovial membrane. But it may be con jectured from the situation and arrangement of the vessels, that a sudden hemorrhage, to any perceptible amount, would necessarily imply the rupture of this delicate tissue, and the consequent presence of the effusion in its cavity ; while a smaller or slower process would carry the membrane before it ; or, in other words, that the presence or absence of the serous covering would chiefly depend on mechanical conditions ; and that, in either case, the result would be little affected.
Indeed, the synovial membrane itself cannot be considered immediately essential to the formation of these substances ; another vas cular surface may be substituted, the result Continuing the same. Thus, Sir Everard
lInniet mentions a case in which thirty or forty such substances were found loose in the Cavity of a false joint, having apparently been mechanically broken off' from a number of projecting portions of cartilage, which studded the broken ends of the bones, leaving exposed interstices. Although slight variations in the size and shape of these substances, and more considerable differences of their consistence, are spoken of, yet their description essentially coincides with that of the preceding bodies examined by Bidder.
Taken altogether, these facts seem to in dicate that the unattached substances which are found in these tissues include the products of very different pathological conditions and processes, They appear to show that morbid deposits beneath the synovial membrane, effu sions the result of violence, and either oc curring beneath it, or by mechanical extension in its cavity, and finally, irregularly formed cartilage, may all, under certain circum stances, give rise to the production of these substances.* The conditions essential to their transform ation seem to be of a twofold nature, me chanical and physiological ; exposure to pres sure and movement, and the presence of a synovial fluid, It is doubtful how far the ac quisition of the peduncle noticed in some, may depend on the joint influence of their extensibility, and the mechanical violence which must be exerted. on such isolated pro • minences. But the separation, whether of these, or of those seen in the false joint, is obviously direct result of violence. Pres sure seems an important condition, so much so, that a close relation may probably be traced between its amount and the degree in which they have assumed the cartilaginous form and consistence ; the synovial sheath, the knee-joint, and the false joint appear to present gradations in both these respects. And as to the operation of the synovial fluid, similar probabilities may be deddced. The mere permanence of these bodies seems to point out that they possess some kind of nu trition; and the increased bulk noticed by Hyrtl in the unattached as compared with the attached substances, would still further ne cessitate such a supposition ; their structure sufficiently denying the suggestion that the increase is due to the union of two or more. And in the case described by Hyrtl, the struc ture of these bodies seems to show that the results of a previous organization are not exempt from this transforming process, but nmy undergo a degeneration into a cartilagi nous substance. And in the absence of any inherent or chemical capacity of their contents for such a change, this vvould yet more re quire the supposition of an agent of nutrition, which should supply the materials, if it did not effect the metamorphosis. While the complete isolation of these bodies from the vessels which are the immediate channels of nutrition, leaves only one supposition, viz., that the synovial fluid is the pabulum from which they derive the materials essential to their permanence, growth, or alteration. The composition of this fluid as cornpared with their own, perhaps sufficiently warrants this conclusion.