Disease of bone or trauma can result in significant bony deformation. Functional impairment as a result of such deformity is an indication for surgical correction. Indicated surgery is often closed wedge osteotomy and internal fixation. Manual design of a preoperative plan using computer-aided design software is the current golden standard for complex correction surgery planning. However, these manually designed plannings are time consuming and subjective. The goal of this study was to develop an algorithm capable of generating good quality preoperative plans for correction surgery, in less time than an expert in preoperative planning.
A software solution integrated in Blender (Blender Foundation, The Netherlands), has been developed to generate semi-automatic preoperative plans. The software optimizes one to three closed wedge osteotomies, by minimizing the dissimilarity from a deformity shape after osteotomy, to a target shape. The deformity shape is the centreline of the deformed femur. The target shape in this study is the centreline of an intramedullary nail.
A cost function was created that makes use of the Hausdorff distance and the root mean squared error to quantify the dissimilarity between the deformity shape after osteotomy and the target shape. Clinical constraints to the model are femoral length and collum anteversion angle. Using a multi-objective genetic algorithm the cost function is minimized within the bounds of the set clinical constraints.
To validate the method of semi-automatic generation, 20 bone models of deformed femora have been created from retrospectively collected CT data. The proposed solution was used to generate preoperative plans, which were scored by two independent assessors. After the creation of an initial preoperative plan and a maximum of two revisions of the plan, 18 of 20 semi-automatically generated preoperative plans were eligible for surgery. Four cases of femoral deformity were randomly selected from the dataset and counterparts to the existing automatic preoperative plans were created manually. 30% to 575% more time was needed to design a preoperative plan manually compared to the semi-automatic generation. In all preoperative plans in the automatic group, the collum anteversion angle of the postoperative configuration was within the normal range of 8-15 degrees. In the manual group, one of four postoperative configurations had a collum anteversion angle within this normal.
The proposed method for semi-automatic preoperative plan generation is a novel, versatile approach with the ability to optimize multiple osteotomies to mimic a given target shape. The automatic planning tool is a promising aide to both technicians and clinicians for a fast preoperative planning withing the boundaries of clinical anatomical normal ranges.

Background: Radiostereometric analysis (RSA) is a technique to assess early migration, which has a predictive value for early failure of unicompartmental knee arthroplasty (UKA). To successfully analyze the RSA images it is important to have a sufficient amount of visiblemarkers with an acceptable three-dimensional distribution.
Objective: To provide insights on marker location distribution by developing a method to analyse marker placement based on visibility and accessibility.
Method: Marker locations in RSA scenes of patients (N=25) from a previous study are used to assess marker placement and analyze marker density by performing a voxelization operation to divide the bone in a grid of 3x3x3mm
bins. After spatial smoothing the hotspots with high marker fractions are determined and the four non-adjacent locations with the highest marker fraction are selected as the most favorable locations. Of these locations the distribution is analyzed by calculating the condition number (CN) of 1000 samples.
Results: The locations of a total of 635 3D markers in the femur and 917 3D markers in the tibia were assessed. After voxelization, the average marker density of non-empty bins was respectively 3.1 and 4.3 markers per bin. The four selected locations had a 47 times higher marker fraction compared to the average bin in the femur and 66 times higher for the selected locations in the tibia. Their mean condition number was 49.1 for the femur and 68.2 for the tibia.
Conclusion: The proposed method has proven to be sufficient for marker
placement analysis. Placing the tantalum markers in the selected locations, which have a considerably higher marker contribution to the total amount of
markers, would presumably increase the marker visibility during RSA and decrease patient exclusion due to an insufficient amount and/or distribution of visible markers.

Introduction: Revision total hip arthroplasty (THA) can be challenging in patients with severe acetabular bone defects and there is no consensus on the preferred reconstruction technique in this population. The aim of this study is to determine the biomechanical differences between Trabecular Metal Acetabular Revision System (TMARS) and Custom Triflange Acetabular Component (CTAC), in patients with Paprosky grade IIIB acetabular bone defects.
Methods: A retrospective study with patients undergoing revision THA surgery TMARS was conducted. For all these patients a virtual CTAC was designed. With this, the TMARS reconstruction could be compared with the virtual CTAC. Assessments of both implants included cortical and cancellous bone contact, center of rotation (COR), inclination, anteversion, and reamed bone volume.
Results: The mean bone contact was 5760 mm2 vs 5447 mm2 for TMARS and CTAC respectively. The TMARS showed significantly more cancellous bone contact than the CTAC (4966 mm2 vs 2887 mm2) and less cortical contact (795 mm2 vs 2560 mm2). The TMARS COR was significantly deviated in the medial-lateral direction compared to the CTAC, with a mean difference of 7.4 mm in lateral direction. TMARS showed a significantly greater reamed bone volume with a mean of 15997 mm3 for TMARS and 2292 mm3 for CTAC.
Conclusion: A semi-automatic method was designed for the determination of the biomechanical differences between TMARS and CTAC reconstructions. TMARS showed significant more cancellous bone contact, but also significant greater reamed bone volume with respect to CTAC. Furthermore, the TMARS COR was localized significantly more lateral compared to CTAC.

Introduction In recent years, there has been an increasing interest in custom triflange acetabular components (CTAC) for revision and oncological surgery. The aim of this study was to evaluate the surgical accuracy of positioning CTACs in patients receiving either total hip arthroplasty (THA) revision or tumor resection surgery, using a novel 3D analyzing technique. Method This retrospective cohort study included 35 patients (27 tumor and 8 THA revision cases), between February 2017 and March 2021. All patients received a CTAC. The planned and achieved implant position were assessed by means of a developed semi-automatic 3D-CT assessment method. The primary outcomes were the cup angles described as inclination, anteversion and cup rotation, and the translation of center of rotation (COR), pubic flange, ischial flange and ilium flange in three planes. Results The mean deviation, between planned and achieved, in inclination was 0.5° (SD: 3.9°), in anteversion 1.2° (SD: 6.1°) and in cup rotation 0.6° (SD: 3.2°). The mean deviation in COR in the sagittal plane was -0.8 mm (SD: 3.2), in the coronal plane -0.4 mm (SD: 6.3) and in the axial plane 0,6 mm (SD: 6,1). Translation of the ischial flange showed the largest aberration (median absolute value: 7.0 mm), followed by the pubic flange (6.4 mm) and the ilium flange (5.3 mm). Discussion A semi-automatic method to analyze the 3D position of CTAC was presented in this study. The results show good agreement between the planned and achieved implant position in patients receiving THA revision or tumor resection surgery. 89% of the components in this study were accurately positioned according to our criteria.

After en bloc resection of primary pelvic bone tumours, orthopaedic oncologists usually try to perform reconstruction in order to achieve limb salvage. Reconstruction after these types of resections is challenging. Especially when the total ilium and parts of the sacrum needs to be removed. One of the reconstructive options is endoprosthetic fixation to sacral bone with the LUMiC prosthesis, but using the LUMiC prosthesis in the sacrum resulted in poor clinical results. Emerging new production techniques such as 3D printing provide for customised prostheses that could be an adequate reconstructive option in these cases and could complement the LUMiC prosthesis to enable sacral anchoring of the LUMiC prosthesis. One of the challenges of customised prostheses is that they are not ‘off the shelf’ and therefore are all different in terms of geometry and, thus, performance. Therefore, these implants cannot be subjected to stringent regulations and registrations used in conventional arthroplasty. In order to ensure maximal safety of these implants we must perform biomechanical testing before implantation. Unfortunately, the bone models for biomechanical testing currently available are not validated on implant fixation and thus unreliable for prosthesis testing. Therefore, in this thesis a new prosthesis that enables sacral anchoring of the cup of the LUMiC prosthesis is designed and two strategies are developed in order to mechanically evaluate this newly designed prosthesis for the sacral anchoring of the LUMiC cup. First strategy is using Finite element modelling to develop a model of the sacrum with implanted prosthesis. Second strategy is the development of 3D bone models of the sacrum using 3D printing together with performing experiments to mechanically evaluate the newly designed prosthesis. Four different mechanical bone models with different shell thickness and infill density were developed and compared to the FE model. Results showed that the new prosthesis design performed better in terms of micromotions between implant and bone compared to the use of the old LUMiC stem in the FE model. Furthermore, a 3D printed mechanical bone model with shell thickness of 1mm and infill structure of 20% showed most comparable results in terms of micromotions between implant and bone compared to the developed FE model. There could be concluded that the FE model and the development of 3D printed mechanical bone models together with the experiments are good starting points in the development of a protocol to in vitro evaluate newly designed 3D printed patient specific prosthesis for the sacrum after tumour resection. The mechanical bone model with shell thickness 1mm and infill structure 20% is the best option in terms of mimicking real bone. Furthermore, the newly designed prosthesis for sacral anchoring of the LUMiC cup showed promising results and could be considered as a improved alternative for the old LUMiC prosthesis stem. In future research cadaver tests should be performed to further validate the found results.