The mode in which wounds of bone combined with loss of substance are repaired is, on the whole, the same as that by which fractures unite. Under favorable circumstances it is effected by the first intention, and the osseous mass exuded from the surfaces of the wound in the bone serves not merely to reunite the bone, but also to supply the place of the part which has been lost. This is true of loss of substance as well of one bone as of another, and in whatever degree, or in whatever form it may have occurred. Irrespectively of unfavorable general conditions, it may be said that the greater the loss of substance, and the more the repair proceeds by way of suppuration and granulation, the less complete will be the reproduction.

Hence it happens that injuries of this kind are followed by permanent loss of more or less of the substance of the bone, and that in long bones shortening, or a false joint is produced.

Wounds of the skull made with a trephine are extremely seldom closed by bony substance altogether, but the circumference of the opening mostly exhibits a growth of bone which may be compared to the two formations of callus. It proceeds from the surfaces of the compact tables as well as from the surfaces and margins of the wound; but is insufficient to close the opening, and the defect is, and continues to be, for the most part supplied by a ligamentous (fibroid) plate, which adheres closely to the dura mater on the one side, and to the pericranium on the other; the trifling amount of (secondary) callus which proceeds from the surfaces of the wound juts into the substance of this plate.

The adjoining part of the wall of the skull is not unfrequently at the same time considerably attenuated, so that the fibroid layer which closes the opening is continuous with a margin of bone, towards which both surfaces of the skull are bevelled off.

In some cases true bone is developed in this fibroid plate. It assumes the form of needles and small plates, and gradually becoming identified with the callus which is growing inwards from the margin, it at length effectuates the closure of the opening by bone. Similar bony growths are met with in false joints in the ligamentous structures by which the fragments are connected together.

The way in which the wounds of bone made in amputations are healed accords with what has been described above: the medullary canal closes, the stump becomes rounded off, and unites with the soft parts and their cicatrix by an intervening cellulo-fibrous tissue, which supplies the place of a periosteum. If the inflammatory process should lead to suppuration in the bone, and still more, if suppuration take place in the periosteum and medulla, necrosis ensues to a corresponding extent; and when the dead piece has exfoliated, the cure is effected by way of granulation.

Under such circumstances, the condition of the stump is sometimes unfavorable: the callus may be insufficient in quantity and density, and therefore incapable of enough resistance: the stump may be attenuated and end in a point; or, on the contrary, the callus may grow from it exuberantly in the form of some of the various osteophytes.