Usage of Finite Element Analysis With Collapsible Elements on Stem Designation

Introduction A Finite Element Analysis (FEA) is often used to examine load transfer between prosthesis and canal. Ordinary, bone elements9 type is defined as elastic material. But using this element type for FEA on stem load transfer, the stems will jump out and fly away when the load is removed even friction between the stem and the canal was defined. This is remarkably different from the reality. It happens because the canal elements return to the original shape without the load. But actually, the bone is impacted by the load without returning to the original shape. Meshing the trabecular bone with a collapsible element type, it can collapse and be hardened by the stem pressure. We have been using Revelation (DJO, USA) with lateral flare for the primary cases whom we can expect high proximal load transfer. We were going to shorten its length to secure proximal load. We have been using Modulus (Lima Corporate, Italy) with conical fixation for the cases we expect mid stem load transfer and neck modification. We were going to extend its length for wider load transfer area. To examine load transfer of the designs the collapsible FEA was used. Objectives Our objectives are to examine load transfer between stems with different length and canal by collapsible FEA. Materials and Methods CAT scan data performed before Hip Arthroplasty were used. Each case has different preferable size. Data conversion was done by Mimics® then LS Dina was used for FEA. For cortical bone and stems conventional elements were used. For trabecular bone, collapsible elements were used. Results With lateral flare stem, more stable proximal load transfer was obtained (Fig. 1). With conical stems, contact pressure on the boundary between stem and bone was widely distributed and no local stress concentration was observed. During stem insertion, trabecular bone was gradually collapsed up to a stable end point. After removing the load, stems were slightly elevated then settled as observed in realty. Conclusions 1.Stem modification for each purpose, load transfer we had expected was obtained. 2.FEA with Collapsible elements has shown results which are closer to the realty.