Necrosis is the death of a bone or part of a bone accompanied by a process of regeneration established at a time coeval or nearly coeval with the inflammation or accident that deprives it of vitality. In this point of view the disease is singular, there being nothing like or ana logous to it in any affection of the soft parts.
Necrosis is rarely a disease of early and never of advanced life, being, except in cases where it attacks the lower jaw, almost exclu sively confined to the period between the ages of ten and tvventy-two : exfoliation may occur at any time, but is more likely to appear in the adult or the aged.
Necrosis, although it may succeed to acci dent, as in this manner compound fractures and other injuries are not infrequently repaired, yet is it more generally an idiopathic disease, or may be the sequela of continued fever; whilst exfoliation in the great majority of instances is the consequence of injury.
According to the acceptation in which we employ the term, it is extremely questionable whether necrosis is ever a disease of the flat bones; at least, except in the instance of the lower jaw, we have never met with an example of the death of one of these structures accom panied or even followed by a regenerative pro cess.
As necrosis, then, presents a solitary exam ple of the efforts of nature in counteracting, or rather in providing against the ravages of dis ease, the process by which it is accomplished becomes an exceedingly interesting subject of inquiry. Different opinions are entertained upon this subject. It seems to be agreed upon all sides that the commencement of the disease is marked by inflammation of the bone: at this period it is red, vascular, and receives the tinge of coloured injections. How this in flammation may be caused or why it is followed by the formation of new bone, are points not so easily determined. Troja introduced a sharp instrument through a bone, by which he con trived to destroy the internal periosteum and marrow, and thus produced a number of cases of necrosis, which presented the same sym ptoms and ran the same course as if they had been examples of idiopathic disease. Hence it came to be believed tha.t the death of the inter nal periosteum was a necessary prelude to necrosis, until it was observed that the parts surrounding a bone had assumed those actions which end in the formation of a new one before the absolute destruction of any part of the old one whatsoever ; and therefore that, although the injury inflicted on the internal periosteum might cause necrosis, yet it was only one cause, and acted by creating inflammation within the substance of the bone. Thus we are obliged to return to the point from which we set out : we know that inflammation is established within the bone, and, coeval with this or nearly so, that nature commences the process of repro duction ; but why this latter is confined to a limited period of our existence, or why even amongst young persons it may occur in .one individual and not in another, form questions to which, in the present state of our knowledge, we can give no answer. We are not even agreed on the different steps of the process or OD the structure principally engaged.
It has been observed that the portion of the bone which is to die, and for some space above and below it, is surrounded by- a dense thick ened mass, of rather a gelatinous character ; that this mass, after a very short time, becomes opaque in detached spots, and that depositions of osseous material are found within it, so that a case of bone may be constructed around the original one before it actually dies, and thus the limb never be entirely deprived of support.* As soon as the dead bone separates from this surrounding mass, the internal surface of this new material becomes, under some circum stances, covered with a layer of lymph, and under others with regular ossific granulations, which gradually increase until a new bone is formed, nearly as serviceable, though not so symmetrical or so beautiful as the old one. It next becomes a question, what is this gelatinous mass, and whence is it derived ? It has been supposed that it was the periosteum of the old bone swelled and thickened, and at the same time softened in consistence; and tbis opinion has been strengthened by Dr. Macartney,1- the
present Professor of Anatomy in the University of Dublin, who stated that he had opportunities of watching the progress of the disease from its earliest periods upwards. According to this gentleman, " the first and most important cir cumstance is the change that takes place in the organization of the periosteum : this membrane acquires the highest degree of vascularity, be comes considerably thickened, soft, spongy, and loosely adherent to the bone ; the cellular sub stance, also, which is immediately connected with the periosteum, suffers a similar alteration : it puts on the appearance of being inflamed, its vessels enlarge, lymph is shed into its inter stices, and it becomes consolidated with the periosteum." Next, " the newly organized pe riosteum, which, for the sake of distinction, one might call the vascular sheath or investment, separates entirely from the bone, after which it begins to remove the latter by absorption, and during. the time that this process is carrying OD, the surface of the vascular investment, which is applied to the bone, becomes covered with little eminences, exactly similar to the granula tions of a common ulcer." To this doctrine Mr: Russell, of Edinburgh, strongly objected. He stated that if the osseous matter was depo sited between the layers of periosteum, both the external and internal surfaces of the new de posit ought to be perfectly smooth, whereas the contrary is observed—they are rough, irregular, and one of them is covered with granulations. He instanced cases of fracture in which, one fragment overlapping the other, and being thus permanently entahgled, the periosteum between the two can have no share in the reproduction, and yet the whole is united by a cylindrical shell of bone, on the principle of reproduction in necrosis. It is also known that compound fractures, where the fragments have been exten sively stripped of periosteum, have united in the same way, and the regeneration of bone, in these instances, could not be attributed to peri osteum, inasmuch as that had been destroyed. It must be owned that this is a very unusual occurrence in compound fractures, but one sin gle example will be sufficient to prove that the reproduction can take place independently of the periosteuin. And again, in cases where disease has caused the sloughing and destruc tion of the periosteurn, as for instance in deeply seated paronychia, still reproduction is some times accomplished by a process resembling necrosis. These argunients seem to be very decisive in overturning the doctrine of the sur rounding- shell being formed by the periosteum, and accordingly Russell supposed that a depo sition takes place from all the surrounding structures ; that it is at first gelatinous ; that it soon assumes the appearance of cartilage ; and that at the end of twenty-four days bony specks may be discovered within it. The external surface of this deposit is rough, and attached to the surrounding parts : its thickness is quite unequal, being greater in proportion to the du ration of the disease, and always more so than the bone it is destined to replace. The internal surface, or that next the old bone, is more smooth, and covered either with lymph or gra nulations. Boyer, Meckel, Weidmann, and other continental surgeons, attribute the process nearly altogether to the periosteum, and there fore their opinions need not be particularly dis cussed ; but it is proper to mention that all the very a.ccurate descriptions we read, of the pro gress from gelatine to cartilage and from carti lage to bone, must be received with the utmost caution. It is by no means usual to meet with cases exemplifying these descriptions ; and amongst a considerable number of dissections of necrosis, it will peihaps be difficult to find one in which the existence of cartilage can be separately and distinctly shown.