A Multi-physics Planning Paradigm for Robot Assisted Orthopaedic Surgery

Osteoporosis or severe reduction in bone mineral density is a disease that primarily affects elderly people. Osteoporotic hip fracture rates increase exponentially with age in both men and women. In addition to the high mortality rate for those sustaining such fractures, less than half of the survivors return to their pre-fracture status concerning the quality of daily living. Augmentation of the proximal femur with Polymethylmethacrylate (PMMA) bone cement (femoroplasty) has been identified as a potential preventive approach to reduce the risk of fracture. Femoroplasty, however, is associated with a risk of thermal damage as well as the leakage of cement or blockage of blood supply when large volumes of PMMA are introduced inside the bone. Several recent studies have proposed injection strategies to reduce the injection volume in simulations. This thesis describes the methods and tools developed for multi-physics planning and the execution of femoroplasty. To this end, computational models are developed to simulate how bone augmentation affects the biomechanical properties of the bone. These models are used to plan femoropasty for cadaveric specimens and showed the superiority of planned-based augmentation over generic injection strategies. Experimental tests confirmed the findings of simulations and showed a significant increase in fracture-related biomechanical properties of the augmented compared to those left intact. In addition to biomechanical studies for femoroplasty, a heat-transfer model was developed to estimate bone temperatures during augmentation. Furthermore, a curved injection strategy was introduced and validated in simulations. These developments and modeling capabilities can be extended to various augmentation surgeries including vertebroplasty and core decompression

Geocaching Motivations

Geocaching is a GPS-enabled treasure hunt. After only about twelve years from its birth, Geocaching has attracted over five million geocachers all around the world. The goal of this study is to understand psychological motivations of Geocaching practices within the community of worldwide geocachers. Understanding Geocaching motivations could lead to improvements in location-based games and also aid in promoting the Geocaching community. Results of two online surveys indicate a variation in Geocaching motivations

Bone Loading in the Upper Extremities (BLUE)

Over 54 million adults in the U.S. are diagnosed with low bone mineral density (BMD). This increases their chance of fractures, especially at the hip or wrist. Because bone adaptation is thought to be driven by strain-producing physical activities, surveys have been made to relate physical activity history to BMD. Current surveys focus on the lower body, but this study examines how physical activity in the upper extremities relates to upper body BMD. Subject testing of 5 basic upper body motions were used to calculate bone loading weighting factors in 34 activities. These weighting factors were used to develop a novel Bone Loading in the Upper Extremities (BLUE) score, but this score was not found to be a significant predictor of BMD (r=0.32, p=0.21)

Comparative Biomechanical Study of Screw Fixation Techniques in Periacetabular Osteotomy

Periacetabular osteotomy (PAO) is a common surgical treatment for developmental dysplasia of the hip. To obtain the optimal method of fixation during PAO, different screw fixation techniques have been proposed for stabilizing the acetabular fragment. This study assesses the biomechanical performance of two popular 3-screw fixation techniques: iliac (IS) and transverse (IT) configurations, through finite element simulations. Additionally, different 2-screw combinations are simulated to investigate the biomechanical significance of each screw of the fixation configurations. The study findings show that yield load of the pelvic bone subject to gait loading for IT configuration is on average 7% higher compared to that of the IS. Although the yield load of the IT is predicted to be slightly higher, no significant difference in bone stiffness and displacement of the acetabular fragment are found between two configurations. Simulation results, therefore, do not demonstrate a significant biomechanical advantage of the IT configuration over the IS. Furthermore, the biomechanical comparison between the 2-screw combinations of IS and IT fixations demonstrates that the most anterior screw in IS, located at the iliac crest, and the most medial screw in the IT are the most critical elements in providing sufficient stability and support for acetabular fragment

EVALUATION OF A BONE REINFORCEMENT TECHNIQUE USING FINITE ELEMENT ANALYSIS

<div><p>ABSTRACT Objectives: To compare the results of a simulated fall on the greater trochanter in the proximal portion of a synthetic femur before and after femoral reinforcement with tricalcium phosphate bone cement (TP) and polymethyl methacrylate (PMMA), using finite element analysis (FEA). Methods: Using two synthetic proximal femurs, a FEA simulating a fall on the greater trochanter was performed, using the Bi-directional Evolutionary Structural Optimization (BESO) program. For this analysis, the femurs were filled with TP and PMMA after perforations were created in the trochanteric region and neck. The results were compared with the strength values obtained from testing the control specimen, a synthetic bone without reinforcement. Results: FEA showed a value of 600 N prior to reinforcement. After cementing with PMMA, the load increased by 57.5% (945 N), and by 53% (920 N) after cementing with TP. Conclusion: Synthetic femurs gained resistance to fracture-causing forces in a simulated fall on the trochanter after bone reinforcement with PMMA and TP. Level of Evidence III; Experimental study.</p></div