Considerations for reporting finite element analysis studies in biomechanics.

Simulation-based medicine and the development of complex computer models of biological structures is becoming ubiquitous for advancing biomedical engineering and clinical research. Finite element analysis (FEA) has been widely used in the last few decades to understand and predict biomechanical phenomena. Modeling and simulation approaches in biomechanics are highly interdisciplinary, involving novice and skilled developers in all areas of biomedical engineering and biology. While recent advances in model development and simulation platforms offer a wide range of tools to investigators, the decision making process during modeling and simulation has become more opaque. Hence, reliability of such models used for medical decision making and for driving multiscale analysis comes into question. Establishing guidelines for model development and dissemination is a daunting task, particularly with the complex and convoluted models used in FEA. Nonetheless, if better reporting can be established, researchers will have a better understanding of a model's value and the potential for reusability through sharing will be bolstered. Thus, the goal of this document is to identify resources and considerate reporting parameters for FEA studies in biomechanics. These entail various levels of reporting parameters for model identification, model structure, simulation structure, verification, validation, and availability. While we recognize that it may not be possible to provide and detail all of the reporting considerations presented, it is possible to establish a level of confidence with selective use of these parameters. More detailed reporting, however, can establish an explicit outline of the decision-making process in simulation-based analysis for enhanced reproducibility, reusability, and sharing.

Cervical laminoplasty construct stability: an experimental and finite element investigation.

STUDY DESIGN: Experimental and finite element investigation of cervical laminoplasty. OBJECTIVE: To determine the stability of the construct post cervical laminoplasty. SUMMARY OF BACKGROUND DATA: Cervical laminoplasty is a widely used technique to widen the spinal canal dimensions without permanently removing the dorsal elements of the cervical spine. Although various laminoplasty procedures have been developed recently, the use of mini-plates to hold the lamina open and prevent restenosis of the spinal cord is a fairly new method and has not been thoroughly investigated. METHODS: Biomechanical compression tests and finite element analyses were performed in this study. Sixteen cervical vertebrae (C3 - C6) were isolated from six cadaveric cervical spines (age at death 68 to 91 years; mean 85 years) and were used for compression tests. Out of the 16 vertebrae, four were without any surgical intervention and the remaining 12 were implanted with one of the two laminoplasty plates: open door (OD) graft. Each vertebra was randomly assigned to one of the three groups: OD plate (6), graft plate (6) or intact vertebrae (4). The intact and implanted vertebrae were potted and loaded to failure. Cross-head displacements and the corresponding reaction force throughout the test were recorded to determine the failure loads. A finite element model of the C5 cervical vertebra was created to accommodate the laminoplasty implants. Experimental loading and boundary conditions were simulated and the stress distribution in the lamina was predicted in response to the compressive loads. RESULTS: A substantial increase in the sagittal canal diameter (27%-33%) and the spinal canal area (31.2%-47%) was observed at all levels. The strength of the implanted specimens was considerably decreased (by six to eight times) as compared to the intact specimens. CONCLUSION: Experimentally obtained data can be combined with mathematical models, such as finite element models, to accurately predict the biomechanical behavior (stresses and strains) of implants and the posterior bone which may not be possible by the use of any other method.

Comparison of hexahedral and tetrahedral elements in finite element analysis of the foot and footwear.

Finite element analysis has been widely used in the field of foot and footwear biomechanics to determine plantar pressures as well as stresses and strains within soft tissue and footwear materials. When dealing with anatomical structures such as the foot, hexahedral mesh generation accounts for most of the model development time due to geometric complexities imposed by branching and embedded structures. Tetrahedral meshing, which can be more easily automated, has been the approach of choice to date in foot and footwear biomechanics. Here we use the nonlinear finite element program Abaqus (Simulia, Providence, RI) to examine the advantages and disadvantages of tetrahedral and hexahedral elements under compression and shear loading, material incompressibility, and frictional contact conditions, which are commonly seen in foot and footwear biomechanics. This study demonstrated that for a range of simulation conditions, hybrid hexahedral elements (Abaqus C3D8H) consistently performed well while hybrid linear tetrahedral elements (Abaqus C3D4H) performed poorly. On the other hand, enhanced quadratic tetrahedral elements with improved stress visualization (Abaqus C3D10I) performed as well as the hybrid hexahedral elements in terms of contact pressure and contact shear stress predictions. Although the enhanced quadratic tetrahedral element simulations were computationally expensive compared to hexahedral element simulations in both barefoot and footwear conditions, the enhanced quadratic tetrahedral element formulation seems to be very promising for foot and footwear applications as a result of decreased labor and expedited model development, all related to facilitated mesh generation.

Effect of miniscrew angulation on anchorage resistance.

INTRODUCTION: Even though the use of titanium miniscrews to provide orthodontic anchorage has become increasingly popular, there is no universally accepted screw-placement protocol. Variables include the presence or absence of a pilot hole, placement through attached or unattached soft tissue, and angle of placement. The purpose of this in-vitro study was to test the hypothesis that screw angulation affects screw-anchorage resistance. METHODS: Three-dimensional finite element models were created to represent screw-placement orientations of 30°, 60°, and 90°, while the screw was displaced to 0.6 mm at a distance of 2.0 mm from the bone surface. In a parallel cadaver study, 96 titanium alloy screws were placed into 24 hemi-sected maxillary and 24 hemi-sected mandibular specimens between the first and second premolars. The specimens were randomly and evenly divided into 3 groups according to screw angulation (relative to the bone surface): 90° vs 30° screw pairs, 90° vs 60° screw pairs, and 30° vs 60° screw pairs. All screws were subjected to increasing forces parallel to the occlusal plane, pulling mesially until the miniscrews were displaced by 0.6 mm. A paired-samples t test was used to assess the significance of differences between 2 samples consisting of matched pairs of subjects, with matched pairs of subjects including 2 measurements taken on the same subject. One-way analysis of variance (ANOVA) with the post-hoc Tukey studentized range test was conducted to determine whether there were significant differences, and the order of those differences, in anchorage resistance values among the 3 screw angulations at maxillary and mandibular sites. RESULTS: The finite element analysis showed that 90° screw placement provided greater anchorage resistance than 60° and 30° placements. In the cadaver study, although the maximum anchorage resistance provided by screws placed at 90° to the cadaver bone surface exceeded, on average, the anchorage resistance of the screws placed at 60°, which likewise exceeded the anchorage resistance of screws placed at 30°, these differences were not statistically significant. CONCLUSIONS: Placing orthodontic miniscrews at angles less than 90° to the alveolar process bone surface does not offer force anchorage resistance advantages.

FEATURE-BASED MULTIBLOCK FINITE ELEMENT MESH GENERATION.

Hexahedral finite element mesh development for anatomic structures and biomedical implants can be cumbersome. Moreover, using traditional meshing techniques, detailed features may be inadequately captured. In this paper, we describe methodologies to handle multi-feature datasets (i.e., feature edges and surfaces). Coupling multi-feature information with multiblock meshing techniques has enabled anatomic structures, as well as orthopaedic implants, to be readily meshed. Moreover, the projection process, node and element set creation are automated, thus reducing the user interaction during model development. To improve the mesh quality, Laplacian- and optimization-based mesh improvement algorithms have been adapted to the multi-feature datasets.

Toward the development of virtual surgical tools to aid orthopaedic FE analyses.

Computational models of joint anatomy and function provide a means for biomechanists, physicians, and physical therapists to understand the effects of repetitive motion, acute injury, and degenerative diseases. Finite element models, for example, may be used to predict the outcome of a surgical intervention or to improve the design of prosthetic implants. Countless models have been developed over the years to address a myriad of orthopaedic procedures. Unfortunately, few studies have incorporated patient-specific models. Historically, baseline anatomic models have been used due to the demands associated with model development. Moreover, surgical simulations impose additional modeling challenges. Current meshing practices do not readily accommodate the inclusion of implants. Our goal is to develop a suite of tools (virtual instruments and guides) which enable surgical procedures to be readily simulated and to facilitate the development of all-hexahedral finite element mesh definitions.

Ia-FEMesh: anatomic FE models--a check of mesh accuracy and validity.

Musculoskeletal finite element (FE) analysis is an invaluable tool in orthopaedic research. Unfortunately, the demands that accompany anatomic mesh development often limit its utility. To ease the burden of mesh development and to address the need for subject-specific analysis, we developed IA-FEMesh, a user-friendly toolkit for generating hexahedral FE models. This study compared our multiblock meshing technique to widely accepted meshing methods. Herein, the meshes under consideration consisted of the phalanx bones of the index finger. Both accuracy and validity of the models were addressed. Generating a hexahedral mesh using IA-FEMesh was found to be comparable to automated tetrahedral mesh generation in terms of preprocessing time. A convergence study suggested that the optimal number of hexahedral elements needed to mesh the distal, middle, and proximal phalanx bones were 3402, 4950, and 4550 respectively. Moreover, experimental studies were used to validate the mesh definitions. The contact areas predicted by the models compared favorably with the experimental findings (percent error < 13.2%). With the accuracy and validity of the models confirmed, accompanied by the relative ease with which the models can be generated, we believe IA-FEMesh holds the potential to contribute to multi-subject analyses, which are pertinent for clinical studies.

An interactive multiblock approach to meshing the spine.

Finite element (FE) analysis is a useful tool to study spine biomechanics as a complement to laboratory-driven experimental studies. Although individualized models have the potential to yield clinically relevant results, the demands associated with modeling the geometric complexity of the spine often limit its utility. Existing spine FE models share similar characteristics and are often based on similar assumptions, but vary in geometric fidelity due to the mesh generation techniques that were used. Using existing multiblock techniques, we propose mesh generation methods that ease the effort and reduce the time required to create subject-specific allhexahedral finite element models of the spine. We have demonstrated the meshing techniques by creating a C4-C5 functional spinal unit and validated it by comparing the resultant motions and vertebral strains with data reported in the literature.

IA-FEMesh: an open-source, interactive, multiblock approach to anatomic finite element model development.

Finite element (FE) analysis is a valuable tool in musculoskeletal research. The demands associated with mesh development, however, often prove daunting. In an effort to facilitate anatomic FE model development we have developed an open-source software toolkit (IA-FEMesh). IA-FEMesh employs a multiblock meshing scheme aimed at hexahedral mesh generation. An emphasis has been placed on making the tools interactive, in an effort to create a user friendly environment. The goal is to provide an efficient and reliable method for model development, visualization, and mesh quality evaluation. While these tools have been developed, initially, in the context of skeletal structures they can be applied to countless applications.