A Finite Element Investigation on the Design of Mechanically Compatible Functionally Graded Orthopaedic Plate for Diaphyseal Tibia Transverse Fracture

The bidirectional stiffness grading of orthopaedic plate has been investigated for internal fixation of transverse fracture in tibia bone. Highly porous cellular materials made of two types of cubic unit cells were designed. Their effective mechanical properties (elastic moduli and yield strengths) were computationally evaluated using finite element analysis. The Gibson-Ashby model was derived for elastic moduli and yield strengths of the cellular geometries. The modified cellular structure provided the desired minimum stiffness within the selected strut sizes. The developed structures were mapped to seven zones of the orthopaedic plate assigning the bidirectional stiffness grading (longitudinal direction). The effect of functional grading on mechanical stimulation through three stages of healing was studied. The results indicated less stress shielding and improvement in uniformity of distribution of equivalent stress around the newly formed bone. Thus, a functionally designed plate will offer a way to dynamically load the healing tissues by encouraging the patient for a regular walk and exercise. Hence, the generated mechanical signal will significantly help mechanically stimulated bone formation and remodeling in the fractured zone.