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Four series of investigations were made on various bone grafting materials and distraction lengthening in cortical bone of adult dogs. Cortical and cancellous bone autografts, non-demineralized and partially HCI-demineralized cortical bone allografts and demineralised allogeneic bone powder were implanted without periosteum and marrow in a three-centimeter cortical bone defect to assess their bridging capacity. Distraction lengthening was applied on the forearm skeleton.
The explanted material was analysed by radiographs, microradiographs, pulse or daily fluorescence labelling, histomorphometry, and mechanical testing for some of them.
One hundred and thirty-five bone grafts and twenty lengthened forearms wereavailable.
From these investigations, several observations were made and can be summarized as follows:
A)Cortical bone autograft
- Bone graft remodelling was already initiated at one month, whether or not the presence of a callus at the anastomotic site.
- Union was achieved in 75% of the anastomotic sites, at six mounts
- In autografts, the intracortical bone resorption an deposition had respectively their peak activities at two and three months after surgery.
- Resoprtion and bone formation had the same temporal pattern in two simultaneous sites of cortical bone defect.
- New bone was deposited on the graft at a slower rate the, in, the bone bed and decreased progressively with the completion of the new haversian systems.
- At nine months, the course of repairs was not fully achieved in autografts as assessed by the porosity level and photon absorptiometric values.
- BMC values of the bone graft was more influenced by the peripheral resorption of the graft than by its porosity level.
- During the course of an autograft incorporation from three to nine months after surgery, the intracortical porosity could influence the mechanical resistance.
B) Cortical bone allografts
- Compared to autografts, allografts were characterized by a marked peripheral resorption which directly influenced the BMC values and the torsinonal strength. Surface bone resorption was more marked in allografts, particularly in the fresh ones, and led to a decreased bone graft diameter with less mechanical resistances. Intracortical porosity was not a distinctive variable among the different bone grafting materials.
- In non-demineralized allografts, new bone was deposited at the same rate as in autografts. Quantitatively, the cumulative new bone index, related to the six-month graft area, was not different from autografts due to the presence of new women bone. However, as the cross-sectional area was greater in autogenous bone, the amount of new bone deposited in autografts was larger in absolute value than in allografts. Lamellar bone formation was earlier and more important in autografts as assessed by the number of double-labeled osteons.
- Creeping-substitution defined as a progressive removal and replacement of non-living bone by new host bone, was the main mechanism in autografts. In allografts, new bone formation resulted also from creeping substitution but in addition, a more extensive removal of cortical bone could occur with its subsequent replacement by new woven bone.
- Autografts were stronger than allografts at six months after surgery because they were less exposed than conventional allografts to a marked peripheral resorption.
- HCI-demineralized segmental allografts were osteoinductive in a fair proportion and responded in an “all-or-nothing” pattern.
- Frozen (-35°C) cortical bone allografts were the most acceptable substitute do autografts when considering their biophysical behaviour compared to the other investigated allografts and the ease of their preservation techniques.
C) Allogeneic inductive bone powder
- Partially HCI-demineralized allogeneic bone powder (200 - 800μ) implanted in the same cortical defect provoked a constant ossification in the gap and in half of the defects, complete bridging with new bone was observed, at six months.
- Membranous ossification was the main mechanism of bone formation. At six months, compaction of the bridging bone was still in progress.
- Autogenous bone marrow supplementation did not appear to influence significantly the final outcome of the inductive material when compared to non-supplemented bone powder.
- At six months, the stage of bone healing was inferior to the one obtained with autogenous cancellous graft used as controls.
- Cancellous bone autografts were found the best bone bridging material in cortical bone defect as they healed without any non-unions and faster than any other bone grafting material.
D) Distraction lengthening of diaphyseal bone
- A directed ossification between two distracted cortical bone segments could be reliably obtained in mature long bones. Most of the new bone arose from a membranous ossification.
- After several days of traction, orientation of the ossification process along the controlled tensile stresses was evident.
- The distracted periosteal and endosteal callus produced a typical pattern of longitudinally-disposed new bone trabeculae growing toward the gap center. From either side, they approached each other and fused.
- Compaction of the new bone was not fully achieved five months after the end of the distraction procedure.
- No evident difference between diaphyseal bone osteotomy and corticotomy emerged as regards to the resulting ossification