1. Traumatic Necrosis.

—Traumatic necrosis is due to the discontinuance of the blood supply by accident or by separation of the whole or a part of a bone in the same way. Thus in consequence of multiple fractures fragments occasionally die and require removal. The same result has been ascribed to traumatic or non-traumatic embolism of the principal nutrient artery of a bone, but the possibility of this condition is doubtful, bone being too well supplied by its surrounding periosteum. Necrosis in connection with fracture is rare except in compound fractures, and, when a detached fragment can be seen, may be anticipated by removal of the same.

2. The Pathological Form.

—The pathological form is due to the preëxistence either of tuberculosis, syphilis, or an acute infection, such as osteomyelitis. It may also be the result of acute infectious periostitis, where the periosteum is completely loosened from the shaft of a long bone. These conditions are connected either with the slow ravages produced by granulation tissue, or with the acute septic processes by which infected exudates shut off large areas from sufficient blood supply, or by which in consequence of septic thrombosis a similar condition results. In consequence there may be met bone dying in small visible particles, or the entire shaft of a long bone or several smaller ones may be involved in the destructive processes.

The portion which dies is known as the sequestrum, which may assume irregular and unusual shapes, varying entirely with the area involved. The general character and size of a sequestrum will depend upon the nature of the cause. In acute osteomyelitis it is either a bone shaft or an epiphysis which thus suddenly dies. In the slower processes the fragments may be of almost any imaginable size and form—irregular with jagged ends, or long, extending completely through a bone, either from end to end or from side to side.

3. The Toxic Forms Of Necrosis.

—The toxic forms of necrosis are due mainly to two substances used in the arts—mercury and phosphorus—whose use seems to be inseparable from the manufacture of many modern industrial products.

Mercurial necrosis may come either from the volatilization of the metal in factories where mirrors are made or from refineries where amalgam is distilled. It also occurs from the internal use of the drug. Its effects are seen more frequently in the alveolar portion of the lower and upper jaw than elsewhere. It is through some unknown peculiarity that the jaws are the bones commonly involved in both of these forms.

Phosphorus necrosis, on the other hand, manifests itself almost entirely in the lower jaw, and occurs usually among the young, in factories where matches are made. It is due to the vapors of phosphorus, which cause a form of nearly distinct maxillary necrosis—a fact which has been so widely recognized as to lead to State legislation preventing the employment of the young in such work.