SIMULATION OF ELECTRIC STIMULATION FOR BONE GROWTH

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Osseointegration is a surgical procedure that provides direct skeletal attachment between an implant and host bone tissue. Osseointegration has proven success in dental, auricle, and transfemoral settings, however, a persistent challenge is achieving adequate long term fixation between implant and bone using natural biological growth. Regulated electrical stimulation has proven effective in fracture healing and non-traumatized bone models, but has not been investigated in a percutaneous osseointegrated implant system. One advantage of the amputee patient population is that an orthopedic implant protrudes from the residual limb functioning not only as an exoprosthesis attachment but also as a potential electrode for an external electrical stimulation device. Therefore, the objective of this collaboration is to build upon the previous, well proven, clinical success of electrically induced bone growth used to augment fracture healing and expand this technology to accelerate osseointegration in the percutaneous model for amputees. Since osseointegration technology is still fairly new for lower extremity amputees and not utilized clinically in the United States, approaches to increasing its efficiency are still developing. The CIBC collaborator group, directed by Dr. Roy Bloebaum, is addressing this limitation by developing an Osseointegrated Intelligent Implant Design (OIID) system which has been awarded a United States provisional patent with the University of Utah Technology Commercialization Office as a novel rehabilitation tool to improve osseointegration technology. The addition of electrical stimulation may increase the rate, magnitude, and quality of initial skeletal attachment to the osseointegrated prosthetic stem. To validate the general hypothesis that electrical stimulation will increase skeletal attachment, a two phase project has been designed that utilizes in vitro, in vivo, and in silico modalities to confirm the safety and efficacy of this technology prior to implementation in amputees. The specific hypotheses for this model are founded on histological assessment, mechanical testing, and finite element analysis. The research hypothesis from the Bloebaum group that is most relevant to the Center is that, "Finite element based simulation analysis of veteran and warrior amputee residual limbs imaged with computed tomography scans will reveal that safe and effective current densities and electric fields will be attainable at the bone-implant interface." To evaluate this hypothesis by creating the necessary simulation infrastructure, the Center has the following technical aims: Aim 1: Develop segmentation and mesh generation support that is adapted to orthopedic applications like this one and to facilitate the rapid generation of accurate geometric models of amputees and the implants and stimulation electrodes required for these modeling applications. Aim 2: Accelerate the computations required to simulate electric fields and current densities for any selected boundary conditions of implant and skin surface electrodes and provide extensive visualization of the results that include certainty and parameter sensitivity. Aim 3: Develop estimation and optimization strategies for locating skin surface electrodes in ways that maximize the growth potential for electrical stimulation of osseointegration.