Stress Simulation and Related Bone Ingrowth in Grooves on Implant Surface

Abstract

Amid increasing numbers of artificial joint implantation surgeries, improving the quality of life (QOL) for patients by accounting for individual variation is a primary concern. Thus, we aim to develop implants designed to optimize the interface between implant and living bone. In particular, for ensuring long-term durability and stability after implantation, we focused on inducement of appropriate alignment for biological apatite (BAp) crystallites and the related collagen (Col) fibers as a bone quality parameter. In this study, we predicted that when stress is applied to bone, the BAp/Col preferential alignment can be formed on the basis of our previous result if osteocytes, which can sense its around stress field, are in an environment that is aligned with the principal stress vector. We tested this idea by introducing grooves with the different angles on the implant surface, considering the principal stress direction. This study finally analyses the effect of stress transmission by a load at the proximal femur on the bone inside and near the grooves by using a mechanical simulation in which groove angles and positions can be changed on the implant surface. Furthermore, we carried out animal experiments using a 2-years-old beagle to examine the effect of grooves in the principal stress direction on the surface in vivo. As a result, bone formation in grooves on the implant surface strongly depends on the grooved angle to the principal stress vector and the grooved position on implants. The new bone preferentially formed inside the grooves parallel to the principal stress direction predicted by three dimensional finite element analysis (FEA) in the proximal area of beagle femur.