Mechanical environment affects allograft incorporation

In a bilateral canine tibial model, the mechanical, radiologic, and histolo gic characteristics of intercalary allografts stabilized with locked intram edullary nails were compared with those of allografts fixed with compressio n plates. Both methods of fixation achieved healing to host bone. Tibiae th at were plated had more callus with statistically greater mean torsional ri gidity and strength than those treated with nails (paired t-test, p less th an or equal to 0.05), On average, tibiae which had been plated had much hig her bending rigidity than those fixed with locked nails; however, the diffe rence in means was not statistically significant. Histomorphometric analysi s showed an overall greater total bone formation in those limbs treated wit h plates compared to nails (paired t-test, p less than or equal to 0.04), T he mechanical environment created by the different fixation methods are tho ught 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 hea ling response in all situations, A less rigid fixation method (plates) prod uced more callus resulting in superior torsional and bending properties. Th ese data show that in this canine intercalary allograft model, limbs fixed with plates produced more external callus resulting in stronger, more rigid healing. (C) 2000 John Wiley & Sons, Inc.