Population-level variability in orthopedic biomechanics

Mechanical stability is the most important requirement for the successful treatment of fractures. The treatment of complicated fractures (e.g., due to osteoporosis) is not sufficiently resolved and is associated with alarmingly high rates of morbidity or mortality. There is a clear difference between the fracture stability due to implant treatment in the experiment and its real performance in fracture care in the patient. One reason for these differences is the lack of consideration of population-specific factors such as gender, age and ethnicity, and thus the associated different anatomy, geometry, structure and material properties of human bones. A recommendation for a given implant or the development of new or improved implant designs requires preclinical assessment of mechanical performance through biomechanical testing. One of the most important considerations in such a test is the substrate in which the implant is being tested. The substrate should mimic the conditions of living human bone as realistically as possible. For this purpose, mainly human donor bones or plastic bones are used. While human bones are expensive, barely available, and potentially infectious, plastic bones from world market leaders are barely able to mimic the mechanical properties of human bones. The aim of this research project is therefore to identify population-specific factors that are relevant for biomechanical implant testing. These factors are then integrated into artificial bone models to provide scientific evidence for optimal anatomical reconstruction for fracture treatment with implants. In summary, bone models for specific orthopedic issues are adapted to the needs of the population and used for the development and validation of implants. Thus, a scientifically sound treatment recommendation for fractures should be able to be pronounced.

Population-specific variability in orthopedic biomechanics The management of challenging fractures (e.g., related to osteoporosis) is not well understood and is linked with disturbingly high rates of morbidity or death. There is a clear contrast between the fracture stability achieved through implant treatment in the experiment and its actual performance in fracture care in the patient. One cause for these variations is a failure to take into account human population-specific characteristics such as gender, age, and ethnicity, as well as the resulting changes in the anatomy, geometry, structure, and material properties of human bones. Preclinical biomechanical testing is necessary to evaluate the mechanical performance of implants and develop innovative designs. One of the most significant factors to consider while performing a biomechanical osteosyntheses test is the bone in which the implant is being tested. The substrate should replicate the circumstances of living human bone as closely as feasible. While human bones are costly, scarce, and possibly infectious, currently available plastic bones can only approximate the mechanical qualities of actual bones. In this project, population-specific mechanical and anatomical characteristics of different genders, age groups and ethnicities were identified and incorporated into artificial bone surrogates. This included anatomical features such as size and geometry of femurs as well as mechanical parameters such as the density of cancellous bone or the thickness of cortical bone. Therefore, polyurethanes were developed which were foamed with blowing agents to achieve real open-cell cancellous structures which were also encapsulated with polyurethanes to produce a real compact bone - both with mechanical properties validated against human bones. These validated polyurethane "recipes" were used to create whole artificial femora. Shape algorithms were used to create average femora geometries of different populations - e.g. female, 75-85 years with European ethnicity, amongst others. These new artificial femora- shaped to several populations and created from novel materials - were validated against human bones in terms of mechanics in bending, torsion and compression. Finally, these new sorrogates were fractured, fitted with osteosyntheses and biomechanically tested in testing machines. The implanted screws showed the same loosening behavior as in human bone; bone surrogates showed the same failure loads and fracture patterns as human bone. To summarize, novel bone models were built, customized to the demands of the human population, and used in implant development and validation to provide scientific proof for the best anatomical reconstruction for fracture repair with implants.