C. ACCIDENTAL CA RTILAGE.-By this name we designate the cartilaginous concretions which are occasionally found in situations where they do not ordinarily exist. They present them selves in several organs, under various forms, and in different stages of development. Laennec divides them into perfect and imperfect ;* but it is not easy to point out any line of distinction between these two classes; they differ only in degree, the one passing gradually into the other as its development becomes more complete. We rarely, indeed, meet with accidental car tilage which deserves to be called poled ; in one part it is fibrous, or of a dense cellular nature, in another it is cartilaginous, while a third portion of the same piece is passing into the osseous state.
The forms and situations in which they occur, will permit an arrangement of them under three heads :— 1. The insulated or loose cartilages, which are found either (a) in joints or (b) in serous sacs.
a. Those of the joints are rounded or ovoid, usually flattened, sometimes lobulated, alvvays smooth, polished, and lubricated with synovia, frequently osseous in their centre. They vary in magnitude from the size of a mustard-seed to that of an almond ; and in one instance Mr. S. Cooper found in the knee a concretion of this kind, which was as large as the patella. They also vary considerably in numbers ; Haller saw twenty in the articulations of the lower jaw, and Morgagni met with twenty-five in a knee-joint. Their most usual seat is in the knee, but they have been found in the hip, jaw, elbow, and wrist. They are commonly " loose," moving freely in the cavity, but some times connected to the synovial sac by slender membranous attachments.
With respect to the origin of these bodies various opinions have been entertained. IIaller and Reimarus supposed that' they were frag ments of the original cartilage, accidentally de tached. Cruveilhier found fifteen of them in a hip-joint some years after it had been injured, and conceived that he saw an exact correspon dence between them and certain depressions in the cartilages of that articulation. Bichat con jectured they might be altered portions of the synovial membrane. According to John Hunter, they may have had their origin in a coagulum of blood poured into the joint from an injured vessel, and there becoming organized. This
coagulum would, he thought, assume, as in all other situations, the peculiar organization of the parts in its immediate vicinity. Laennec and Beclard were of opinion that they might be formed outside the synovial membrane, and push it before them so as to form a pedicle, which in some cases remained, but more gene rally was ruptured. This opinion Laennec sup ported by observations made on similar sub stances in serous sacs, where he traced them through all the degrees of their development, from the incipient stage, in which they formed a slight projection behind the membrane, to the period when they became perfectly isolated bodies. Sir Benjamin Brodie, whose authority on this subject is of so much weight, remarks, " It is generally supposed that these loose bodies have their origin in coagulated lymph which has been effused from inflammation of the inner surface of the synovial membrane, and which has afterwards become vascular. In the majority of cases, however, which I have met with, no symptoms of inflammation pre ceded their formation; and hence it is probable that, in some instances, they are generated like other tumours, in consequence of some morbid action of a different nature. They appear to be situated originally either on the external sur face, or in the substance, of the synovial mem brane ; since, before they have become de tached, a thin layer of this latter may be traced to be reflected over them." When inflammation is of long standing in a bursa mucosa, it is not unusual to find in it a number of loose bodies, of a flattened oval form, and of a light brown colour, with smooth surfaces, resembling small melon-seeds in ap pearance. There seems to be no doubt that these bodies have had their origin in the coagu lated lymph effused in the early stage of the disease.t From the resemblance which these concretions bear to loose cartilages, we might infer that they both have bad a similar origin ; but, as there can be no doubt that loose car tilages sometimes begin to be formed outside the synovial membrane, we must not conclude that this is the only mode.