3D fabrication of short-stem porous hip implant design for preventing stress shielding & promoting osseointegration

Author(s): Seyed Ataollah Naghavi

Currently, total hip replacement surgery is an effective treatment for osteoarthritis, where the damaged hip joint is replaced with an artificial joint. Stress shielding is a mechanical phenomenon that refers to the reduction of bone density as a result of altered stresses acting on the host bone. Current orthopaedic prostheses undergo too much stress shielding due to their solid metallic nature, which are much stiffer than the surrounding bone. During physical activities, these mechanical properties mismatch between the implant and the native bone causes the stiffer prosthesis to absorb a substantial percentage of stress, leading to stress shielding. This study aims to develop a hip stem which can distribute the physiological loads from the hip stem to the femoral bone. It is well known that metallic porous structures have a very good force distribution feature, these are now manufactured via metal 3D printing technology. 3D printed porous hip implants can help reduce this stress shielding effect and transfer a more distributed force to the surrounding bone. It has also been shown that graded density implants have an optimal lower stress value compared to the uniform porosity and conventional hip implants. This means that the graded density implants have a reduced stress shielding. Inverse Homogenization has also being used in recent studies to ensure mechanical compatibility among topology optimized microstructures This would simultaneously optimize the physical properties of the individual cells as well as those of neighbouring pairs, to ensure material connectivity and smoothly varying physical properties. The architected hip implants presented in recent studies shows clinical promise in reducing bone loss while preventing implant micromotion. These graded porous structures can also promote bone tissue in growth into the implant, resulting in long term implant fixation, which eventually prolongs the life of implant and delays the need for revision surgery.