The aim of the study is to develop a workflow to establish geometrical quality criteria for 3D printed anatomical models as a guidance for selecting the most suitable 3D printing technologies available in a clinical environment. Methods: We defined the 3D geometry of a 25-year-old male patient's L4 vertebra and the geometry was then printed using two technologies, which differ in printing resolution and affordability: Fused Deposition Modelling (FDM) and Digital Light Processing (DLP). In order to measure geometrical accuracy, the 3D scans of two physical models were compared to the virtual input model. To compare surface qualities of these printing technologies we determined surface roughness for two regions of interest. Finally, we present our experience in the clinical application of a physical model in a congenital deformity case.Results: The analysis of the distribution of the modified Hausdorff distance values along the vertebral surface meshes (99% of values <1 mm) of the 3D printed models provides evidence for high printing accuracy in both printing techniques. Our results demonstrate that the surface qualities, measured by roughness are adequate (~99% of values <0.1 mm) for both physical models. Finally, we implemented the FDM physical model for surgical planning. Conclusion:We present a workflow capable of determining the quality of 3D printed models and the application of a high quality and affordable 3D printed spine physical model in the pre operative planning. As a result of the visual guidance provided by the physical model, we were able to define the optimal trajectory of the screw insertion during surgery.
Interbody devices are widely used to replace the degenerated discs of the spine. For this purpose, a novel methodology uses cement instead of conventional spacers, which is hypothesized to provide smoother transition of forces, lower risk of bone tissue damage, thus smaller subsidence, reduced risk of further pathological deformations and other complications. This new treatment approach has been compared with the conventional method experimentally by mechanical loading of human vertebral motion segments treated with either of these. The present study aimed at complementing the that work with finite element analysis and, by performing in silico mechanical testing of QCT-based case specific models incorporating the elasto-plastic behavior of bone, providing better understanding of experimental results, in particular, the differences between the two sample groups equipped with the different spacer types. This report presents the applied numerical methodology as well as the first results, which are in line with the experimental ones. Besides providing deeper insight into the experimental outcomes, these models are expected to provide a basis for virtual parameter analysis studies, which may help to optimize the surgical procedure.
The first human pancreatic leiomyosarcoma xenograft (PZX-7) growing in immuno-suppressed mice is described and characterized.
Introduction Degenerative spinal changes are often accompanied by osteoporosis in elderly patients. In these cases traditional interbody devices can strongly subside into the irregular deformed endplates and vertebrae during or after the surgical stabilization. To avoid implant subsidence, a new technique is developed where PMMA bone cement is applied as a custom-made interbody device providing better contact and more even load transfer along the vertebra-implant interface. The aim of this study was to compare the biomechanical properties of the two different spacer types. In this presentation, we focus on the connection between the bone mineral density and geometrical parameters of vertebrae and the compression failure of the spinal segment. Materials and Methods 22 monosegmental human cadaveric lumbar specimens were included in the analysis (Group “C” - cement: N = 12, Group “S” - spacer: N = 10). There were 8 steps to prepare the specimens: 1, isolation of a human cadaveric lumbar segment; 2, parallel embedding of cranial and caudal free endplates; 3, qCT scanning and vBMD measurement before applying interbody device; 4, introducing either a D-shaped PEEK spacer (Sanatmetal) or a custom made PMMA (Cemex) spacer as interbody device; 5, CT scanning after applying interbody device; 6, performing uniaxial compression tests (Instron 8872) and analyzing results (failure load and displacement, stiffness, elastic limit load and displacement); 7, CT scanning after the compression test; 8, finite element model was built to analyze the failure process using CT data. Results Comparison of initial geometrical data (vertebral cross sectional area, height, volume) and vBMD of “C” and “S” groups showed no significant difference. Failure load was similar in both groups. However, in the “S” group, there was a significant correlation between vBMD and failure load (R=0.73, p < 0.05), while such correlation was not observed (R = −0.04, p < 0.90) in the “C” group. The same association was observed for vertebral cross sectional areas (“S”: R=0.78, p < 0.01; “C”: R = −0.47, p < 0.20), vertebral height (“S”: R=0.94, p < 0.00; “C”: R = −0.27, p < 0,50), volume (“S”: R=0.85, p < 0.00; “C”: R = −0.49,p < 0.20) and failure load. Conclusion Analysis of mechanical test results showed that application of a PMMA cement spacer yields a significantly stiffer construct with smaller risk for subsidence compared with a PEEK spacer. However, load, that caused irreversible mechanical failure of the segments, were similar in both groups. In case of the PEEK spacer, the failure load does not depend on bone quality only, but on vertebral size parameters as well. In case of the PMMA cement spacer, such correlations were not observed. Finite element models showed completely different load transfer and failure process in the two groups. This difference is in line with our results above. In case of a relatively small vertebral size and poor bone quality, a prefabricated PEEK intervertebral cage may be associated with higher risk of mechanical failur...
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