Strain distribution in plated and unplated sheep tibia - An in vivo experiment

After plate osteosynthesis changes in bone biology and bone mechanics are o bserved in the plated bone segment. Compromise of the vascular supply in th e plate bed leads to a remodelling process and to a temporary porosity in t he bone cortex underneath the plate. In addition, the plate takes over some of the physiological loading of the bone, which in turn alters the normal strain distribution of the cortical bone tissue. The aim of the present stu dy is to determine the tissue deformation of the sheep tibia in vivo and th e changes in tissue strain due to plating with plates of different rigiditi es. Measurements were performed on the intact bone at the mid diaphysis using t he strain gauge technique. With different connections on the tension bridge (Wheatstone bridge), the strain was measured separately for pure axial loa ding, bending, and torsion before and after plating with a 4.5 mm stainless steel or titanium DCP. Under physiological load the sheep tibia is mainly deformed in torsion (62% ) and bending (33%), and much less in axial loading (5%). Plating with a st eel plate reduces the overall tissue strain by 18%, with a titanium plate b y 13%. This reduction is mainly due to a reduction in axial tissue strain d ue to axial loading and bending and less to the reduction of tissue strain under torsion. In our in vivo model, plating with steel or titanium plates leads to a redu ction of the physiological tissue strains. The difference between the diffe rent plates is small due to the fact that the high tissue strain under tors ion is only slightly affected by plating. Thus, from the purely mechanical paint of view and with regard to preserving normal tissue strains as much a s possible, titanium plates offer little advantage compared with stainless steel plates. But, titanium as an implant material may offer advantages wit h respect to tissue compatibility and infection resistance.