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Accuracy of 3D Printed Spine Models for Pre-Surgical Planning of Complex Adolescent Idiopathic Scoliosis (AIS) in Spinal Surgeries: A Case Series

Dutta, A., Singh, M., Kumar, K., Navarro, A.D., Santiago, R., Kaul, R.P., Patil, S., Kalaskar, D.M., 2023. Bahl, J. S., Arnold, J. B., Saxby, D. J., Taylor, M., Solomon, L. B., Thewlis, D., 2023. . Annals of 3D Printed Medicine, 11, 100117.

Context

"Adolescent idiopathic scoliosis (AIS) is a noticeable spinal deformity in both adult and adolescent population. In majority of the cases, the gold standard of treatment is surgical intervention. Technological advancements in medical imaging and 3D printing have revolutionised the surgical planning and intraoperative decision making for surgeons in spinal surgery. However, its applicability for planning complex spinal surgeries is poorly documented with human subjects. The objective of this study is to evaluate the accuracy of 3D printed models for complex spinal deformities based on Cobb angles between 40¡ã to 95¡ã.This is a retrospective cohort study where, five CT scans of the patients with AIS were segmented and 3D printed for evaluating the accuracy. Consideration was given to the Inter-patient and acquisition apparatus variability of the CT-scan dataset to understand the effect on trueness and accuracy of the developed CAD models. The developed anatomical models were re-scanned for analysing quantitative surface deviation to assess the accuracy of 3D printed spinal models. Results show that the average of the root mean square error (RMSE) between the 3DP models and virtual models developed using CT scan of mean surface deviations for the five 3d printed models was found to be 0.5¡À0.07 mm. Based on the RMSE, it can be concluded that 3D printing based workflow is accurate enough to be used for presurgical planning for complex adolescent spinal deformities. Image acquisition and post processing parameters, type of 3D printing technology plays key role in acquiring required accuracy for surgical applications."

Use of Simpleware Software

"The 3D solid models of the patient's scoliotic spines were obtained using an image analysis software package from Simpleware ScanIP (²ÝÁñÉçÇø., UK). The process comprised of the following steps: segmentation of the CT-scan images based on Hounsfield Units (HU) of cortical bone (HU 100-2000), mask development, smoothing of the contours of each slice using manual segmentation, and preparing a solid model of the spine from the masks. The segmentation and surface mesh quality were checked for irregularities, holes and overlapping edges. The segmentation of each spine data formed the ground-truth (models developed from the patients CT scan data) comparison for the corresponding 3D printed model segmentation, which was used to evaluate the accuracy of the 3D printing workflow. The methodology from data acquisition to generation of 3D printed model is described in Fig. 1. The created 3D surface model from patient CT-Scan was then exported for 3D printing in STL file format for 3D printing of the spinal models."

"Image acquisition and segmentation form the backbone in determining the accuracy of printed models. Image acquisition needs to be performed by software for medical purposes. This study used commercially available Simpleware ScanIP (²ÝÁñÉçÇø Inc., UK). Auto segmentation is helpful for most bone segmentation, but complex structures demand manual segmentation. Knowledge of human anatomy helps to understand anatomical structures to perform complex segmentation such as in AIS. Auto segmentation was checked manually for any inaccuracies and corrected, to ensure accuracy of segmentation process for complex spinal anatomies."

Outcomes and Impact

"This work critically examined the capabilities of patient specific 3D printed spinal models for complex scoliosis surgery with Cobb angle varying from 40 to 95¡ã. The work demonstrated that FFF based 3D printing workflow could be adapted for presurgical planning of complex adolescent scoliotic patients. This provides clinically acceptable level of accuracy for surgical planning and screw placements practice within 0.5 mm accuracy, shows promise for this technology adoption for safer surgical planning for complex AIS. The benefits and drawbacks for both patients and staff and the long-term clinical efficacy and safety of using 3D printed models need to be further evaluated if we are to see more widespread uptake. This would require larger patient cohorts and long-term studies to investigate this expanding clinical field."

Custom Knee Prosthesis Design for Additive Manufacturing

Stanca, V., Braileanu, P.I., 2023. . Academic Journal of Manufacturing Engineering, 21(1), 72-77.

Context

"This work aims to develop a customized knee joint prosthesis, starting from the traditional preoperative planning of total knee arthroplasty surgery and using morphoanatomical parameters extracted from the patient's CT scans. The customized model of the knee prosthesis is made using a three-dimensional virtual preoperative planning method, similar to the traditional preoperative planning performed by surgeons. The CT scans of a patient were segmented, using specific algorithms to extract the bone tissue that forms the knee joint, and then the obtained model was imported into the CAD application software, where, with the help of evaluation tools, all the femoral and tibial patient¡¯s landmarks were identified. Based on these morpho-anatomical landmarks, a 3D model of the knee prosthesis was built, which was used in additive manufacturing of the prototype."

Use of Simpleware Software

"The bone segmentation technique enables improved diagnosis, disease characterization and treatment monitoring using CT scans. There are numerous software applications dedicated to performing bone segmentation automatically by applying several algorithms of direct bone tissue extraction and image processing. In this study, Simpleware ScanIP software was used, which is a software dedicated to the processing of medical images. Moreover, the mentioned software has a base of complex image processing algorithms in this way, a better surface and a more finished model can be obtained. The bone segmentation begins by importing DICOM files into the software used. The DICOM set used in this study case contains 1563 whole-body CT images of a 43-year-old male.

Threshold?based techniques can be used to separate bone tissue from soft tissue using higher levels of HU values (Hounsfield units) in CT scans. The HU values attributed to bones in other studies are found between 150HU and 3000HU. A threshold will be set for both the lower and upper limits of the gray levels identified in the histogram. The lower limit will have the value of +200HU, and the upper one the value of 2000HU. After setting the thresholds, the region of interest is selected for the actual bone segmentation). Fig. 1 shows the selection of the right femur in all MPR windows in Simpleware ScanIP software. To separate the femur from the pelvis, the Split regions function was used, through which different masks can be created, and the regions of interest can be manually selected to make the segmentation more precise. In this case, a mask for the pelvis (blue color) and a mask for the femur (purple color) were created.

After the regions were well defined, the mask corresponding to the pelvis was removed, leaving only the mask corresponding to the femur. The segmentation of the femur was successfully completed, but gaps can be observed in the viewing window of the axial plane. They must be removed, as they can influence subsequent measurements. The Paint with threshold tool is used to cover the bone tissue. Finally, the model can be exported with the *.stl or *.step extension, which can later be used in CAD software applications to create virtual simulations or to prepare surfaces for additive manufacturing. The same steps are followed for the segmentation of the tibia and patella."

"Anatomical surfaces possess irregular geometric shapes with a high complexity. This affects the processing time and analysis of the CAD model, but also the computer performance requirements. To avoid the disadvantages of anatomical surfaces, the models resulting from the processing of CT images in Simpleware ScanIP software are simplified, to optimize the analysis and processing time. This is possible by obtaining surfaces with reduced complexity of the model geometry."

Outcomes and Impact

"The main objective of this article was fulfilled by designing a total knee joint prosthesis using morpho-anatomical parameters with the help of virtual preoperative planning that can reduce postoperative complications caused by the geometry of the prosthesis and the components orientation. The prototyping process of a customized knee prosthesis according to the morpho-anatomical parameters of the patient is a long one compared to the choice of using a prosthesis that comes from a range of prostheses with different sizes. 

Although the prototyping of a total knee prosthesis may seem difficult due to the need of different software and implicitly an engineer qualified in this field, most of these processes can be automated or semi-automated by developing medical imaging processing software where the anatomical parameters of the patient can be automatically measured which later they can be transformed into an editable geometric model depending on the desired parameters."

Custom Humeral Joint Prostheses Using Additive Manufacturing and Biocompatible Smart Materials

Manole, C.S.T.M., Braileanu, P.I., Dobrescu, T.G., Chiscop, F., 2023. . Materiale Plastice, 60(3), 19-30.

Context

"Personalizing prosthetic components based on individual anatomical landmarks can increase implant lifespan and it can reduce the postoperative complications due to prosthesis geometry that does not mold on the patient¡¯s anatomy. This article aims to present a method of optimizing shoulder prostheses by conducting both medical and technological studies, based on which a personalized prototype was obtained, designed according to the patient's landmarks. Thus, a computer-assisted methodology has been developed that targets the preoperative planning of shoulder arthroplasty starting from the traditional planning used by orthopedic surgeons, as well as the principles of determining the relevant humeral parameters. Initially, a set of DICOM CT (Digital Imaging and Communications in Medicine) patient scans with a presumed fracture at the glenohumeral joint requiring a shoulder arthroplasty was used. The acquired data were transferred to a medical image processing software, where was performed the bone segmentation, specifying the image processing algorithms used to reconstruct the geometry of the patient's shoulder. The 3D model of the humerus obtained during thisstage was imported into a CAD (Computer Aided Design) software application where the humeral anatomical landmarks were established and used to design a suitable prosthesis according to patient's needs, which was manufactured through additive manufacturing using a biocompatible material."

Use of Simpleware Software

"To reconstruct the geometric structure of the bone and subsequently obtain the CAD model of the humerus, the bone segmentation process was performed using Simpleware ScanIP, a software program designed for medical image processing. The Simpleware software provides the user with a range of complex processing algorithms that can be applied to CT scans to obtain solid 3D models of the region of interest [6-8], thus accelerating and optimizing the preoperative planning methodology. Furthermore, it plays a crucial role in conducting virtual analyses and preparing the model for additive manufacturing."

Outcomes and Impact

"Summarizing, this work involved detailed studies on the anatomical structure of the glenohumeral joint, analyzing both the causes and pathologies that lead to shoulder prosthetics, as well as the degrees of freedom associated with the targeted joint. The goal was to demonstrate the beneficial impact that medical engineering can have on improving the quality of life for patients. Furthermore, the study emphasizes the idea of uniqueness in relation to each human body, highlighting the need for personalizing prosthetic components based on the specific humeral anatomical parameters of each individual patient. The aim is to increase the longevity of the implant to reduce revision surgeries, particularly among younger patients with severe shoulder conditions. 

Moreover, building upon existing commercial solutions, this work opted for developing a prosthetic system characterized by simplified geometry using CAD software. The humeral component has the ability to vary in inclination by ¡À15¡ã, as seen in more advanced humeral prostheses. However, its fully anatomical design is intended to provide adequate joint biomechanics, ensure implant stability, and enhance the range of motion for patients. In future research, is desired to adjust the simplistic design of the humeral prosthesis prototype to obtain a complex 3D model with variable geometry for better precision in restoring humeral joint mobility. This approach promotes joint stability and increased range of motion without compromising the fixation of the implant. In the components manufacturing process, 3D printing technology was used with an FDM 3D printer and biocompatible ABS material called SmartFil Medical, scientifically certified for short-term contact with the human body.

The future trends in this field aim to optimize the morphology and functionality of the humeral endoprosthesis, closely mimicking the anatomy and biomechanics of the glenohumeral joint. This includes improving bone segmentation and virtual prototyping through the development of specialized medical software for preoperative planning of shoulder arthroplasty, using the VTK library in Python programming language. Future perspectives also involve conducting virtual finite element analysis simulations to simulate the mechanical behavior of the customized humeral endoprosthesis and conducting a comparative study with a standardized prosthesis to identify weak areas and further improve the prototype. The impact of these additional research efforts is valuable in avoiding errors in the reconstruction of the normal shoulder joint by designing a highly accurate 3D model, aiming to achieve a personalized shoulder prosthesis that closely mimics the patient¡¯s anatomical structure and morphology."

Fabricating Patient-Specific 3D Printed Drill Guides to Treat Femoral Head Avascular Necrosis

Bell, C.E., Feizi, A., Roytman, G.R., Ramji. A.F., Tommasini, S.M., Wiznia, D.H., 2023. . Research Square, Preprint.

Context

"Background: Femoral head avascular necrosis (AVN), or death of femoral head tissue due to a lack of blood supply, is a leading cause of total hip replacement for non-geriatric patients. Core decompression (CD) is an effective treatment to re-establish blood flow for patients with AVN. Techniques aimed at improving its efficacy are an area of active research. We propose the use of 3D printed drill guides to accurately guide therapeutic devices for CD.

Methods: Using femur sawbones, image processing software, and 3D modeling software, we created a custom-built device with pre-determined drill trajectories and tested the feasibility of the 3D printed drill guides for CD. A fellowship trained orthopedic surgeon used the drill guide to position an 8 ga, 230 mm long decompression device in the three synthetic femurs. CT scans were taken of the sawbones with the drill guide and decompression device. CT scans were processed in the 3D modeling software. Descriptive statistics measuring the angular and needle-tip deviation were compared to the original virtually planned model.

Results: Compared to the original 3D model, the trials had a mean displacement of 1.440¡À1.03 mm and a mean angle deviation of 1.093¡À0.749?.

Conclusions: The drill guides were demonstrated to accurately guide the decompression device along its predetermined drill trajectory. Accuracy was assessed by comparing values to literature-reported values and considered AVN lesion size. This study demonstrates the potential use of 3D printing technology to improve the efficacy of CD techniques."

Use of Simpleware Software

"A foam cortical shell femur (Model SKU 1103, Sawbones, Vashon, WA, USA) was scanned using a LightSpeed VCT GE Medical Systems CT Scanner with a slice thickness of 0.625 mm and 80 kVp. The CT scan was segmented using ²ÝÁñÉçÇø Simpleware ScanIP software (Version 2022, Sunnyvale, CA, USA), creating a 3D femur model. To represent the necrotic lesion, a virtual lesion was positioned in the head of the 3D femur model, which was based on previously described lesions in the literature."

"The foam femur CT scans were rendered as 3D model masks using ScanIP image processing software. The 3D model masks from the accuracy tests were individually overlaid on the original modeled femur with the ideal drill trajectory (Fig. 2). The ScanIP measurement tool was used to find the positional deviation and angular deviation between theoretical and experimental drill trajectories. Positional deviation was determined by measuring the difference in drill tip location between the ideal drill trajectory and the test drill trajectories. Angular deviation was determined by measuring the angle between the guidewire and the ideal drill trajectory from the cortical entry point. Descriptive statistics (mean and range) were collected for the angle deviation and needle tip deviation."

Outcomes and Impact

"Our 3D printed drill guide prototype was determined to be accurate and reliable. Using this technique in surgical practice can provide several advantages over conventional techniques such as reducing time and thereby infection risk in CD surgery as well as lowering the cost of surgery. Although the 3D printed drill guide has the potential to improve the accuracy of core decompression procedures, further research is needed to fully evaluate its effectiveness and feasibility in a surgical setting."

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