Rheological characteristics of tibial regenerated bone

Purpose. To evaluate the deformable characteristics of the regenerated bone for stepwise increasing and decreasing axial load. Materials and Methods. The authors developed the intravital assessment of bone fragmental fixation stiffness in the Ilizarov fixator at FSBI RISC “RTO”; the assessment is based on determining the changes in the distance between the wires coming out of bone for limb axial loading. The deformable characteristics of the regenerated bone for limb stepwise increasing and decreasing axial loading with 5 kg-increment each for 10 seconds were evaluated in patients with acquired (n=24) and congenital (n=21) shortening of the leg at the stage of fixation. The index of regenerated bone deformability (E) was used in order to characterize fixator-segment system stiffness; the index was calculated as the value of mutual displacement of the wires inserted through proximal and distal bone fragments at the graduated load of 15 kg with respect to the height of the distraction regenerated bone (the value dimensional representation - µm/mm×15 kg). The deformability value (E) of the regenerated bone is determined by the rate of distraction and by the amount of bone lengthening. Results. A decrease in the relative deformability and residual deformation of the regenerated bone at the stage of fixation reflects an increase of the regenerated bone stiffness in fixator-segment system. The period within first 2-3 weeks of fixation is the “period of risk” of the regenerated bone deformity development in patients with the disease congenital etiology. As for patients with the disease acquired etiology, there is no such “period of risk” in them. The investigation of the regenerated bone deformable characteristics using walking as a functional test is a quantitative criterion of the adequacy of fixator-segment system load and stiffness. The test result is considered as positive if residual deformity decreases after walking. One can speak of the yield strength raising and recommend limb axial load increasing for patients. The test result is considered as negative if residual deformity increases after walking - it is recommended to decrease axial load of the limb or to increase fixator-segment system stiffness. Conclusion. Studying the regenerated bone deformable characteristics is an additional technique to evaluate distraction regenerated bones.