Nicole A. Kallemeyn

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.

Validation of a C2–C7 cervical spine finite element model using specimen-specific flexibility data

This study presents a specimen-specific C2-C7 cervical spine finite element model that was developed using multiblock meshing techniques. The model was validated using in-house experimental flexibility data obtained from the cadaveric specimen used for mesh development. The C2-C7 specimen was subjected to pure continuous moments up to +/-1.0 N m in flexion, extension, lateral bending, and axial rotation, and the motions at each level were obtained. Additionally, the specimen was divided into C2-C3, C4-C5, and C6-C7 functional spinal units (FSUs) which were tested in the intact state as well as after sequential removal of the interspinous, ligamentum flavum, and capsular ligaments. The finite element model was initially assigned baseline material properties based on the literature, but was calibrated using the experimental motion data which was obtained in-house, while utlizing the ranges of material property values as reported in the literature. The calibrated model provided good agreement with the nonlinear experimental loading curves, and can be used to further study the response of the cervical spine to various biomechanical investigations.

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.

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.

Hexahedral meshing of subject-specific anatomic structures using mapped building blocks.

To extend the use of computational techniques like finite element analysis to clinical settings, it would be beneficial to have the ability to generate a unique model for every subject quickly and efficiently. This work is an extension of two previously developed mapped meshing tools that utilised force and displacement control to map a template mesh to a subject-specific surface. The objective of this study was to map a template block structure, common to multiblock meshing techniques, to a subject-specific surface. The rationale is that the blocks are considerably less refined and may be readily edited after mapping, thereby yielding a mesh of high quality in less time than mapping the mesh itself. In this paper, the versatility and robustness of the method was verified by processing four data-sets. The method was found to be robust enough to cope with the variability of bony surface size, spatial position and geometry, producing building block structures (BBSs) that generated meshes comparable to those produced using BBSs that were created manually.

Biomechanical Effects of Laminoplasty and Laminectomy on the Stability of Cervical Spine

Cervical spondylotic myelopathy is the most common spinal cord disorder in persons more than 55 years of age in North America and perhaps in the world [7]. It is a chronic degenerative condition of the cervical spine that results in the reduction of spinal canal diameter and thereby compresses the spinal cord and the associated nerve roots [1].Copyright

Growing multiblock structures: a semi-automated approach to block placement for multiblock hexahedral meshing

Finite element (FE) analysis is a cornerstone of orthopaedic biomechanics research. Three-dimensional medical imaging provides sufficient resolution for the subject-specific FE models to be generated from these data-sets. FE model development requires discretisation of a three-dimensional domain, which can be the most time-consuming component of a FE study. Hexahedral meshing tools based on the multiblock method currently rely on the manual placement of building blocks for mesh generation. We hypothesise that angular analysis of the geometric centreline for a three-dimensional surface could be used to automatically generate building block structures for the multiblock hexahedral mesh generation. Our algorithm uses a set of user-defined points and parameters to automatically generate a multiblock structure based on a surfaces geometric centreline. This significantly reduces the time required for model development. We have applied this algorithm to 47 bones of varying geometries and successfully generated a FE mesh in all cases. This work represents significant advancement in automatically generating multiblock structures for a wide range of geometries.

Advancements in Spine FE Mesh Development: Toward Patient-Specific Models

Laboratory-driven experimental studies are capable of delineating the biomechanical characteristics of the spine. They are limited, however, to external responses; that is, internal stresses and strains throughout the structures are not readily attained. Mathematical simulations provide a unique opportunity to serve as an adjunct to experimental studies to predict the external responses, while complementing the experiments by providing such internal responses. Musculoskeletal finite element (FE) analyses have emerged as an invaluable tool in orthopaedic-related research. While it has provided significant insight into the biomechanics of the spine, the demands associated with modeling the geometrically complex structures often limit its utility. Individualized models are important for future development of this field, as they offer a means of correlating mechanical predictions with clinical outcomes. However, relatively few FE studies to date have employed specimen- or patient-specific models. Spine modeling is by no means an exception. In this chapter we describe multiblock methods for generating subject-specific spine meshes to alleviate the current limitations of spine meshing. In addition, we demonstrate additional computational tools to perform “virtual surgery,” and show examples of how the techniques have been applied to date.

Finite Element Model of Multi Level Cervical Laminoplasty

Cervical spinal stenosis is a medical condition caused by the narrowing of the spinal canal, possibly leading to the compression of the spinal cord or other nerve roots [1]. Surgical options include an anterior approach involving decompression and fusion or a posterior approach involving laminectomy and fusion or laminoplasty. Laminoplasty, considered an alternative to laminectomy, is a procedure intended to relieve pressure on the spinal cord while maintaining the stabilizing effects of the posterior elements of the vertebrae.Copyright

Cervical Laminoplasty Construct Stability: A Finite Element Study

Cervical laminoplasty is one of many modern techniques utilized in the management of cervical myelopathy. In the United States cervical spondylotic myelopathy (CSM) has been classically treated with multilevel decompression and fusion. Furthermore, multi-level anterior cervical decompression and fusion (ACDF), via disectomies or corpectomies, and multi-level cervical laminectomy and fusion have been well described [1]. In the last decade cervical laminoplasty has grown in popularity as a non-fusion alternative that allows multi-level cervical decompression.Copyright