## 1 Introduction
Furthermore, this route results in improved cost-benefit analysis as the higher quality implants (more accurate anatomical-fit) minimize clinical complications, reduce operating room times, and can eliminate the need for second surgery fixation removal [17; 18]. Topology optimization has become a design tool pillar of part shape optimization due to its ability to mathematically generate optimal structures based on the original structure considering a defined objective function (e.g., strain energy) and constraints (e.g., volume and stress). Topology optimization has been shown and proven to be a suitable technique primarily to optimize designs by redistributing the material based on the loading conditions and removing any material regions that have minimum contribution to the design's mechanical stability. The reason why this is optimal for osteosynthesis application is that it can tailor the mechanical stiffness of the plate without changing its parent material and compromise its instability. Since 2006, it has been a popular and feasible approach to design biomedical implants and has been employed in designing joint replacement prosthetics [19], osteosynthesis and reconstruction implants [20; 21]. Topology optimization was previously used to address shielding by optimizing the medical implant designs of pelvic prosthetics [22], femur hip joints [23], generic bone plates [24] and spinal cages [25], showing improved bone-implant load transfer. In addition, in the case of [26], the authors presented a topology-optimized mandible fixation plate able to perform and withstand the imposed physiological loads. A topology optimization model of medical implants could be constructed as a stand-alone model without including a bone model to optimize the implant based on its mechanical behavior. However, this will eliminate an important role of the implant's biomechanical behavior. This is why, in this study, topology optimization considered a physiological loading including bone and screws, aiming to minimize the risk of stress shielding. In addition, the adaptation of topology optimization to the patient-specific computer tomography (CT) data is significant in order to optimize plates specific for each patient. This allows medical imaging and topology optimization techniques to integrate, rapidly producing optimized specific plates and accommodating the patient's condition (implant size, injury type, normal or osteoporotic bone, etc.). However, topology optimization is known to present designs with complex internal/porous structures which are not possible to be manufactured using conventional techniques [27; 28; 29]. Additive manufacturing (AM) is considered to be the ideal technology to fabricate these complex structure; additionally, AM is able to fabricate parts with no complex tooling and achieve a reduction in material waste, and it is significantly reliable in producing medical implants for mass personalization [30; 31; 32]. The scope of this study is to combine medical imagining and topology optimization to address stress shielding, promote better load transfer and reduce surgery and post-surgery complications. The purpose of this paper is to present the validity to create a topology-optimized patient-derived custom-fit bone plate. A spiral distal tibia fracture was considered to optimize a distal tibia fixation plate. The custom-fit plate was initially designed considering a computer tomography (CT) scan of a patient's tibia. Afterwards, the plate's initial design was topology optimized considering three volume reductions (25%, 50% and 75%) and a gait loading condition on the CT scanned fractured tibia. Stress finite element analyses were performed to evaluate the initial design and topology-optimized plates to investigate the implant-bone load transfer on the defined bone fracture planes. Finally, a three-dimensionally (3D) printed polymer prototype was fabricated to visualize the optimized plates.