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In contrast to this picture of inactivity on the part of the transplant is the active growth of bone occurring on its periosteal surface. Here, even though there is no intimate contact with the cleft spinous process, a layer of new bone has formed.

Summarizing these facts, it is clear that the graft acts in two ways: first, passively, as a kind of scaffold, for the ingrowth of bone derived from the osteogenetic tissues into

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Fig. 50.—Camera lucida drawing of a part of the cancellous bone forming the deeper layers of the graft. In this cancellous bone many nuclei have retained their normal staining capacity-microscopic evidence that they are still alive.

which it has been implanted; second, as an active factor by the osteogenetic function of its periosteal and endosteal cells. Most of the bone cells die, but some of them, particularly those of the cancellous tissue, live. These, however, do not show evidences of marked proliferative capacity, as do the periosteal cells, although the microscopic picture in some instances is suggestive of their power of amitotic division.

An important element in the success of bone grafting is the power of functional development inherent in bone (Wolff's law). It has been shown that bone will respond to abnormal stress and strain by changes in its architecture to meet the new mechanical conditions. Fig. 51 illustrates an instance of this adaptability of bone. It is a cross-section of a tibial

transplant for Pott's disease (Albee operation). The cortex of the tibia was transplanted. At autopsy, a year and a half later (death due to amyloid disease) the bone was found to have assumed the tubular form with cortex and medullary cavity, exactly as in one of the long bones.

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Fig. 51.—Microscopical cross-section of a cortical graft from the tibia inserted by the Albee technique in a case of Pott's disease. Specimen recovered 142 years after operation. The cortical graft has assumed the shape of a tubular bone with cortex, marrow cavity and periosteum. The specimen illustrates the functional adaptation of the graft to its new environment. (Wolf's Law.)

The operative technic must be based upon a knowledge of the laws of bone regeneration. That method is to be considered most physiological in which the osteogenetic elements of the transplant are afforded the best opportunity for development, and in which the significance of the underlying mechanical laws are properly appreciated. These requirements are in my experience best met by the technique devised by Albee (see "Bone-graft Surgery,” W. B. Saunders Co.). The essential principle in this method is the implantation of the graft in such a way as to bring each one of its constituent parts into intimate contact with the corresponding elements of the recipient bone.

Application to Gunshot Injuries.-Exactly the same technic is applicable to these as to the pseudo-arthroses produced in other ways. In two respects only must great caution be

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b Fig. 52.—Pseudarthrosis of the ulna subsequent to gunshot injury. a, Three weeks after insertion of a graft. b, Two months later showing fracture of the graft. Healing by callous, produced by osteogenetic function of the engrafted bone.

exercised: first, operation must be postponed until all signs of infection have been absent 4 months, otherwise healing will occur in only a small percentage of the transplants; second, more than the normal precaution must be used in the after treatment, since, owing to the extensive loss of bone and to the scar formation fracture of the graft can easily occur (see Fig. 52).

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Fig. 53a.-A gunshot injury of the lower portion of the humerus. The diastasis of 2 in. was successfully bridged by a bone transplant as shown in Fig. 53b.

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Fig. 53b.-Pseudarthrosis of humerus due to extensive loss of substance produced by gunshot injury. a, Three months after the injury. b, After a bone graft by the Albee method. Healing by primary union occurred despite the presence of shell fragments. Particular care was taken to plan the operative incision so as to avoid these possible foci of infection.

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6 Fig. 54.-a, Tracing of roentgenogram of pseudarthrosis of the sternum produced by extensive gunshot injury. Respiration caused the patient intense pain because of the rubbing of the fragments against one another. b, the same, subsequent to the implantation of a strong tibial graft. The patient's pain disappeared immediately after the operation.

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