A BIOMECHANICAL STUDY OF THE PELVIS WITH AND WITHOUT FRACTURES AND IMPLANTS: COMBINING COMPUTATIONAL DESIGN AND EXPERIMENTAL TESTING FOR TYPICAL DAILY MOVEMENTS

This study fulfills the need for a dedicated pelvis testing setup that is widely accepted with physiological relevance. There is limited comparative biomechanical data available for the Supraacetabular External Fixator (SEF) and the Subcutaneous Iliopubic Plate (SIP) used in the treatment of anterior fragility fractures of the pelvis (FFP). Most experimental studies so far have relied on simplified loading and boundary conditions. There has been a growing interest in personalizing motion analysis to develop customized implants that can optimize implant performance and accelerate fractured bone recovery for individual patients. Therefore, the main objective of this study is to develop a biomechanical test bench that can emulate the physiological gait loading of the pelvis, experimentally evaluate the stabilizing effect of the SEF and the SIP in the treatment of FFP, expand the test stand's capability to emulate other common daily movements, investigate the impact of customized musculoskeletal (MS) models, and assess the potential benefits of using personalized 3D metallic printed subcutaneous plates for the treatment of FFP type Ia fractures. The study uses the Computational Experiment Design procedure to design a biomechanical test stand that realistically emulates the pelvis' physiological gait loading. The test stand is designed to iteratively reduce all muscles and joints' contact forces of the pelvis to only four force actuators while still producing a similar stress distribution in the pelvis. The study conducts repeatability and reproducibility tests to ensure the test stand's capabilities. Next, the FFP type Ia is created on a synthetic pelvis for biomechanical testing under gait loading. The osteotomy on the right pelvic ring is then stabilized with the SEF or the nonlocking/locking SIP, and the stability provided by both implants is assessed numerically and experimentally under physiological loading. Motion analysis is conducted to calculate joint and muscle force envelopes for the common daily movement of interest. Stress, strain and displacement of the pelvis under these loads are assessed numerically and then implemented in the biomechanical test stand to emulate each movement following the computational experiment design concept. A metallic 3D-printed SIP is developed to match the anatomical landmarks of the insertion points on the pelvis used in the experiments. This 3D printed plate is assessed numerically and experimentally under physiological load to evaluate its performance compared to conventional plates. Personalization of the MS model is conducted for the pelvis by matching the anatomical landmarks of the pelvis in the generic MS model and the model of the pelvis used in the actual experiments. The developed test stand and the concept of computational experiment design behind it provide guidelines on how to design biomechanical testing equipment with physiological relevance. The boundary conditions and the nature of loading adopted in this study are more realistic regarding physiological relevance compared to the state-of-the-art. The numerically developed biomechanical testing setup of the pelvis in this study is a significant step forward in developing a physiologically relevant pelvis testing setup