Mechanical environment affects allograft incorporation.
In a bilateral canine tibial model, the mechanical, radiologic, and histologic characteristics of intercalary allografts stabilized with locked intramedullary nails were compared with those of allografts fixed with compression plates. Both methods of fixation achieved healing to host bone. Tibiae that were plated had more callus with statistically greater mean torsional rigidity and strength than those treated with nails (paired t-test, p </= 0.05). On average, tibiae which had been plated had much higher bending rigidity than those fixed with locked nails; however, the difference in means was not statistically significant. Histomorphometric analysis showed an overall greater total bone formation in those limbs treated with plates compared to nails (paired t-test, p </= 0.04). The mechanical environment created by the different fixation methods are thought to be responsible for the observed differences in healing pattern. The traditional concept of fixation for allografts to achieve maximum rigidity of the construct may not necessarily promote the most appropriate host healing response in all situations. A less rigid fixation method (plates) produced more callus resulting in superior torsional and bending properties. These data show that in this canine intercalary allograft model, limbs fixed with plates produced more external callus resulting in stronger, more rigid healing.