Implant Strength Contributes to the Osseointegration Strength of Porous Metallic Materials.

Creating the optimal environment for effective and long term osseointegration is a heavily researched and sought after design criteria for orthopedic implants. A validated multi-material finite element model was developed to replicate and understand the results of an experimental in-vivo push-out osseointegration model. The finite element (FE) model results closely predicted global force (at 0.5mm) and stiffness for the 50%-90% porous implants with an r2 of 0.97 and 0.98 respectively. In addition, the FE global force at 0.5mm showed a correlation to the maximum experimental forces with an r2 of 0.90. The highest porosity implants (80-90%) showed lower stiffnesses and more equitable load sharing but also failed at lower a global force level than the low porosity implants (50-70%). The lower strength of the high porosity implants caused premature plastic deformation of the implant itself during loading as well as significant deformations in the ingrown and surrounding bone, resulting in lower overall osseointegration strength, consistent with experimental measurements. The lower porosity implants showed a balance of sufficient bony ingrowth to support osseointegration strength coupled with implant mechanical properties to circumvent significant implant plasticity and collapse under the loading conditions. Together the experimental and finite element modeling results support an optimal porosity in the range of 60 to 70% for maximizing osseointegration with current structure and loading.