In vitro Effects of External Fixation on Intact and Osteotomized Tibiae: A Biomechanical Study

Abstract

To study the in vitro mechanical effects of external fixation on intact and osteotomized bone, human and rabbit tibiae were tested in 3-point bending in an Instron testing machine. Intact tibiae were loaded in the elastic range before and after application of an external fixation device. In the human specimens the Vidal-Adrey double frame was used; in the rabbit specimens, external minifixation. Bone deformation in the anteroposterior direction was measured with a linear voltage differential transformer. After application of external fixation a median bone elastic stiffness of 110.2% in human tibiae and of 106.1% in rabbit tibiae was found, in relation to the stiffness of intact tibiae without external fixation. The stiffness increase was significant in human specimens but not significant in rabbit specimens. In osteotomized human tibiae fixed with the Vidal-Adrey double frame, a median stiffness of 8.5% of the stiffness of intact bones was found when compression was not applied, compared to 19.9% when compression was applied. In rabbit tibiae a median stiffness of osteotomized bones with external mini-fixation was 8.9% of the stiffness of intact bones. There was a good agreement between the results in rabbit tibiae with the mini-fixation and the human tibiae with external fixation without compression. External mini-fixation thus seems to be a suitable model for the study of bone healing in rabbit tibiae.