Bone disease can have a devastating impact on an individual’s life quality and expectancy. Bone fracture is characterized as the most prevalent musculoskeletal disorder that necessitates hospitalization and it is a common consequence of osteoporosis. Bone microarchitecture is highly affected by bone diseases, such as osteoporosis and osteoarthritis, through the alteration of its structure and integrity. It has been proven that the visualization and quantification of bone structure on the micro-scale is a crucial requirement for the early detection of bone fractures and disorders. Photon Counting Detector Computed Tomography (PCD-CT) is a novel clinical imaging system that provides the potential of high spatial resolution scans while using low radiation dose. However, its inherent advantages over traditional CT scanners have not been widely investigated yet. The aim of this study was to evaluate the efficiency of PCD-CT in quantifying features of bone microstructures like bone volume fraction, trabecular thickness, separation and number, in various radiation dose
levels. The capabilities of PCD-CT in bone morphological analysis were further investigated through the comparison against the gold-standard techniques of Micro-Computed Tomography (micro-CT) and High Resolution Peripheral Quantitative Computed Tomography (HR-pQCT). Four pairs of cadaver bones acquired from different anatomical locations (radius, tibia, vertebrae, femoral head) of the same individual were scanned with three CT scanners, PCD-CT, micro-CT and HR-pQCT, using micro-CT as reference standard. The bones of vertebrae and femoral head were scanned within a human body-simulating phantom, as well. The average measurement of the four bone parameters was calculated using an automated volume-based fitting and a voxel-counting algorithm. The image quality of PCD-CT was also assessed by estimating the trabecular sharpness and contrast to noise ratio, through an algorithm which analyzed the histogram values of localized bone and fat regions. The comparison between PCD-CT and micro-CT/HR-pQCT extracted data was realized through the
statistical analysis processes of Bland & Altman and linear regression analysis. The results of this study indicated that the ratio of bone volume to total volume as well as the thickness and separation of trabeculae were overestimated by PCD-CT in comparison to the micro-CT, in the bone scans of all cadaver bones. In the case of bones within the phantom, the thickness and separation of trabeculae were overestimated but the bone volume to total volume was underestimated compared to micro-CT. The number of trabeculae was consistently underestimated in both cases in which the bones were scanned within the phantom or not. In the comparison against HR-pQCT, the bone volume to total volume ratio, number and thickness of trabeculae were overestimated by PCD-CT whereas the trabecular separation was underestimated. Through this study, it was indicated that the correlation between PCD-CT and micro-CT or HR-pQCT extracted bone parameters improves as higher doses are used during PCD-CT scanning. However, the agreement between the extracted bone parameters does not necessarily increase in the same way. Overall, PCD-CT featured sufficient image resolution and sharpness to evaluate the morphology of the bone, in both low and high radiation doses, with
the highest image quality being achieved through the high dose values. These outcomes suggest that PCD-CT could hold great promise for analysing the bone microstructure in the peripheral and central human skeleton, revolutionizing the diagnosis and treatment of bone pathologies.

Slipped Capital Femoral Epiphysis (SCFE) is the most common hip disorder in adolescents characterised by the displacement of the femoral head relative to the femoral neck through the growth plate [3]. In-situ fixation, the current standard type of treatment, stabilises the epiphysis to prevent further slippage. Although it prevents further slippage of the femoral head, the altered morphology of the proximal femur remains [4], leading to long-term complications. Recent studies have, however, revealed that bone growth can continue after fixation, suggesting potential for guided bone growth through strategic screw placement. The aim of this study is to find the optimal screw position for in-situ fixation to stimulate longitudinal bone growth in desired areas, thereby potentially improving the femur morphology and reducing SCFE severity. The study is divided into two parts: the first part focuses on modeling healthy bone growth to validate the computational approach against results from a prior study and clinical data, while the second part concentrates on SCFE analysis to explore the optimal screw position for in-situ fixation to stimulate longitudinal bone growth in desired areas. A finite element (FE) model of a femur with a mild slip was developed to predict bone growth under various screw positions. The Osteogenic Index (OI), which quantifies the expected amount of bone growth, was used to predict growth patterns. The findings indicate that the conventional center-center screw position, commonly used in surgical practice, results in minimal bone growth. Conversely, anteriorly positioned screws, particularly in the anteromedial (AM) and anterolateral (AL) regions, were associated with the most significant and beneficial growth on the posterior side of the growth plate. The expected amount of growth in the AM and AL positions was approximately 211% and 138% greater, respectively, than in the conventional center-center position. These results suggest that anterior screw placement could enhance bone growth in desired areas, potentially mitigating the severity of SCFE and improving long-term functional outcomes. These results reinforce similar findings of a prior retrospective clinical study by [2]. This study contributes to a growing body of evidence supporting the reconsideration of traditional screw placement strategies in SCFE treatment. The insights gained could inform surgical practices aimed at optimising growth modulation and improving patient outcomes. Recommendations have been given to improve the FE analysis and validation. The largest uncertainty lies in the hip contact force in SCFE patients. Further research is needed to investigate this loading for different patients and slip severities and test the influence of the loading conditions on the growth pattern. In addition, clinical trials are necessary to fully validate these findings and assess their practical implications in the treatment of SCFE.

Acetabular component revision surgery in people with severe acetabular bone defect is challenging and associated with higher failure rates compared to primary total hip arthroplasty. This MSc Thesis project aimed to assess the static strength of a novel custom triflange acetabular component (CTAC) by experimental testing and finite element (FE) modelling. Experimental validation of the developed FE model showed that the simulation underestimated the axial displacement of the femoral head as well as most implant strains. However, most numerically found implant strains showed a good linear correlation with the experimentally measured implant strains. Based on the experimental and numerical results, it was concluded that the developed CTAC has sufficient static strength to resist excessive static loads in multiple physiologically relevant directions. The developed CTAC has the potential to decrease the high failure rates currently associated with acetabular component revision surgery.

Additive manufacturing (AM) provides the opportunity for complex porous designs, without the costs depending on batch size. Therefore patient-specific implants can be rapidly manufactured. In clinical practice, reconstruction of the mandible is needed in case of bone tumors or trauma. Part of the mandible is removed and the shape of the missing part needs to be estimated, before an implant can be designed. Now-a-days the golden standard for mandible reconstruction is autograft surgery using the iliac or fibula bone. However, this comes with extra donor site surgery and asymmetrical face contours. Mandible movements are needed for mastication and speech and the mandible bone accounts largely for the individual’s face appearance. Hence, good estimation is needed for both function and aesthetics
In this study, a statistical shape model (SSM) of the mandible was generated by segmentation of the mandibles from 35 full body CT-scans. The missing shape of the mandible was estimated using an extruded base, the SSM and mirroring of the intact side. Two finite element models (FEM) were made; one of a healthy mandible and one with a 25% total volume defect with a solid Ti-alloy implant created with the SSM. Two loading conditions were simulated separately; incision clenching (INC) and right molar biting (RMB). Topology optimizations were made with a volume constraint of 0.2 and 0.24 together with an objective function to minimalize the strain energy. To investigate more initial conditions, more topology optimizations were completed. These included one in which the initial implant included pores and two in which extreme mandible cases were used, which were retrieved using the b-values for the first mode of the SSM.
Variations in shape of the mandible were seen in the modes of the SSM. Mode 1 described the variations in shape between the intercondylar angle and distance, mode 2 of the gonial angle and symphysis length, mode 3 described the variations in shape and position of the condyle and mode 4 was associated with the coronoid process. Calculations of the maximum and average distances of the point cloud of the original missing bone part to the estimated shapes illustrated that both mirroring of the healthy side and SSM resulted in the closest estimation. No significance was found between the two methods. Limitations of the mirroring method in relation to the locations of the defects, resulted in the use of SSM for the design of the implant. Topology optimization resulted in optimized implant frames that were located at lateral inferior sides of the implants for both volume constraints and biting tasks. Small differences were seen in the exact location of the crossing of the implant frame. FEM results suggested correct maintenance of stress concentrations and displacements, when compared to the healthy intact mandible. It was suggested that the initial implant shape influences the optimized outcome. Different mandibles resulted in unique optimized implant frames, making the outcome patient specific. The workflow created in this study can be used as a proof of concept for the design and optimization of patient-specific implants for mandible reconstruction, which can easily be manufactured using additive manufacturing processes.