Subaxial lateral mass prosthesis for posterior reconstruction of cervical spine

Purpose: To obtain the relevant morphometry of the lateral mass of the subaxial cervical spine (C3-C7) and to design a series of lateral mass prostheses for the posterior reconstruction of the stability of cervical spine. Methods: The computed tomography (CT) scans of healthy volunteers were obtained. RadiAnt DICOM Viewer software (Version 2020.1, Medixant, Poland) was used to measure the parameters of lateral mass, such as height, anteroposterior dimension (APD), mediolateral dimension (MLD) and facet joint angle. According to the parameters, a series of cervical lateral mass prostheses were designed. Cadaver experiment was conducted to demonstrate its feasibility. Results: 23 volunteers with an average age of 30.1 ± 7.1 years were enrolled in this study. The height of lateral mass is 14.1 mm averagely. Facet joint angle, APD and MLD of lateral mass averaged 40.1 degrees, 11.2 mm and 12.18 mm, respectively. With these key data, a lateral mass prosthesis consists of a bone grafting column and a posterior fixation plate was designed. The column has a 4.0 mm radius, 41 degrees surface angle and adjustable height of 13, 15, or 17 mm. In the cadaver experiment, the grafting column could function as a supporting structure between adjacent facets, and it would not violate exiting nerve root (NR) or vertebral artery (VA). Conclusion: This study provided detailed morphology of the lateral mass of subaxial cervical spine. A series of subaxial cervical lateral mass prostheses were designed awaiting further clinical application.

A comparative study of 3D printing and heat-compressing methods for manufacturing the thermoplastic composite bone fixation plate: Design, characterization, and in vitro biomechanical experimentation

Metallic bone fixations, due to their high rigidity, can cause long-term complications. To alleviate metallic biomaterials’ drawbacks, in this research new Glass Fiber/Polypropylene (GF/PP) composite internal fixations were developed, and an investigation of their mechanical behavior was performed through in vitro biomechanical experiments. Short randomly oriented, long unidirectional prepreg, and long unidirectional fiber yarn were considered as reinforcements, and the effects on their mechanical properties of different manufacturing processes, that is, 3D printing and heat-compressing, were investigated. The constructed fixation plates were tested in the transversely fractured diaphysis of bovine tibia under axial compression loading. The overall stiffness and the Von Mises strain field of the fixation plates were obtained within stable and unstable fracture conditions. The samples were loaded until failure to determine their failure loads, strains, and mechanisms. Based on the results, the GF/PP composite fixation plates can provide adequate interfragmentary movement to amplify bone ossification, so they can provide proper support for bone healing. Moreover, their potential for stress shielding reduction and their load-bearing capacity suggest their merits in replacing traditional metallic plates.

Finite Element Analysis as an Iterative Design Tool for Students in an Introductory Biomechanics Course

Insufficient engineering analysis is a common weakness of student capstone design projects. Efforts made earlier in a curriculum to introduce analysis techniques should improve student confidence in applying these important skills toward design. To address student shortcomings in design, we implemented a new design project assignment for second-year undergraduate biomedical engineering students. The project involves the iterative design of a fracture fixation plate and is part of a broader effort to integrate relevant hands-on projects throughout our curriculum. Students are tasked with (1) using computer-aided design (CAD) software to make design changes to a fixation plate, (2) creating and executing finite element models to assess performance after each change, (3) iterating through three design changes, and (4) performing mechanical testing of the final device to verify model results. Quantitative and qualitative methods were used to assess student knowledge, confidence, and achievement in design. Students exhibited design knowledge gains and cognizance of prior coursework knowledge integration into their designs. Further, students self-reported confidence gains in approaching design, working with hardware and software, and communicating results. Finally, student self-assessments exceeded instructor assessment of student design reports, indicating that students have significant room for growth as they progress through the curriculum. Beyond the gains observed in design knowledge, confidence, and achievement, the fracture fixation project described here builds student experience with CAD, finite element analysis, 3D printing, mechanical testing, and design communication. These skills contribute to the growing toolbox that students ultimately bring to capstone design.

127 Standardising Access to Fracture Fixation Simulation for Core Surgical Trainees

Introduction Simulation is increasingly being used to augment clinical experience. However, access to simulation varies geographically and national courses can be costly. The Severn School of Surgery aimed to provide a locally run, cost-neutral “Basic Principles in Fracture Fixation” course to standardise access to simulation for core surgical trainees (CSTs). Method The course ran from a district general hospital, accommodating lectures, case discussions, and practical stations (screw fixation, plate fixation, dynamic hip screw, and external fixation). Faculty donated their time and a devices company provided kit and dry bones. CSTs organised the course. Pre- and post-course self-rated Intercollegiate Surgical Curriculum Programme (ISCP) global competency ratings in the practical stations were recorded and usefulness of aspects of the course was recorded. Results 32 candidates attended. Mean self-rated competency increased by at least one global rating in all practical stations (p < 0.05). All aspects of the course were deemed useful (pre-course reading by 27/28, lectures by 31/32, and case discussions by 31/32). No net cost was incurred. Conclusions Increases in self-rated competency in surgical skills can be obtained through a cost-neutral, trainee-organised, regional skills course. Pre-course reading, lectures, case discussions, and practical sessions are all useful. This model can be used by others to standardise the simulation curriculum.

Migrated PEG balloon causing acute pancreatitis

Percutaneous endoscopic gastrostomy (PEG) is a common procedure for an unsafe swallow or inability to maintain oral nutrition. When a PEG tube needs replacement, a balloon gastrostomy tube is usually placed through the same, well formed and mature tract without endoscopy. We present a patient with a rare complication related to the balloon gastrostomy tube, to raise awareness and minimise the risk of this complication in the future. A 67-year-old female patient presented to the emergency department with severe abdominal pain and vomiting. Her gastrostomy feeding tube displaced inwards, up to the feeding-balloon ports complex. After investigations, she was diagnosed with acute pancreatitis. MR cholangiopancreatography (MRCP) confirmed features of this and, interestingly, an inflated gastrostomy balloon could be seen abutting the major and minor ampullae. The patient confirmed that the PEG tube had been changed to a balloon gastrostomy tube some time ago, but the external fixation plate (external bumper) had been loose lately, with the tube repeatedly moving inwards. She admitted that, 1 day before admission, the PEG tube had receded into the stomach and could not be pulled out with a gentle tug. After reviewing the MRCP images, the balloon was deflated, and the tube retracted. Once correctly placed, the balloon was reinflated, and her symptoms improved over the next 2 days.

Experimental validation of finite element simulation of a new custom-designed fixation plate to treat mandibular angle fracture

Background The objective of the study was to validate biomechanical characteristics of a 3D-printed, novel-designated fixation plate for treating mandibular angle fracture, and compare it with two commonly used fixation plates by finite element (FE) simulations and experimental testing. Methods A 3D virtual mandible was created from a patient’s CT images as the master model. A custom-designed plate and two commonly used fixation plates were reconstructed onto the master model for FE simulations. Modeling of angle fracture, simulation of muscles of mastication, and defining of boundary conditions were integrated into the theoretical model. Strain levels during different loading conditions were analyzed using a finite element method (FEM). For mechanical test design, samples of the virtual mandible with angle fracture and the custom-designed fixation plates were printed using selective laser sintering (SLS) and selective laser melting (SLM) printing methods. Experimental data were collected from a testing platform with attached strain gauges to the mandible and the plates at different 10 locations during mechanical tests. Simulation of muscle forces and temporomandibular joint conditions were built into the physical models to improve the accuracy of clinical conditions. The experimental vs the theoretical data collected at the 10 locations were compared, and the correlation coefficient was calculated. Results The results show that use of the novel-designated fixation plate has significant mechanical advantages compared to the two commonly used fixation plates. The results of measured strains at each location show a very high correlation between the physical model and the virtual mandible of their biomechanical behaviors under simulated occlusal loading conditions when treating angle fracture of the mandible. Conclusions Based on the results from our study, we validate the accuracy of our computational model which allows us to use it for future clinical applications under more sophisticated biomechanical simulations and testing.

Design and simulation of a resorbable bone fixation plate made by additive manufacturing for femoral mid-SHAFT fractures

<p class="JARTEKeywords">Finite element method has been employed to establish the feasibility of a fixation plate made of PLA by additive manufacturing for femoral shaft fractures. For this purpose, Von Mises stress and the pressure contact between bones had been analysed. The proposed design has been compared with an actual titanium fixation plate as a point of reference.</p>