Nicole A. DeVries

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.

Biomechanical Analysis of Cervical Disc Replacement and Fusion Using Single Level, Two Level, and Hybrid Constructs

Study Design. A biomechanical study comparing arthroplasty with fusion using human cadaveric C2–T1 spines. Objective. To compare the kinematics of the cervical spine after arthroplasty and fusion using single level, 2 level and hybrid constructs. Summary of Background Data. Previous studies have shown that spinal levels adjacent to a fusion experience increased motion and higher stress which may lead to adjacent segment disc degeneration. Cervical arthroplasty achieves similar decompression but preserves the motion at the operated level, potentially decreasing the occurrence of adjacent segment disc degeneration. Methods. 11 specimens (C2–T1) were divided into 2 groups (BRYAN and PRESTIGE LP). The specimens were tested in the following order; intact, single level total disc replacement (TDR) at C5–C6, 2-level TDR at C5–C6–C7, fusion at C5–C6 and TDR at C6–C7 (Hybrid construct), and lastly a 2-level fusion. The intact specimens were tested up to a moment of 2.0 Nm. After each surgical intervention, the specimens were loaded until the primary motion (C2–T1) matched the motion of the respective intact state (hybrid control). Results. An arthroplasty preserved motion at the implanted level and maintained normal motion at the nonoperative levels. Arthrodesis resulted in a significant decrease in motion at the fused level and an increase in motion at the unfused levels. In the hybrid construct, the TDR adjacent to fusion preserved motion at the arthroplasty level, thereby reducing the demand on the other levels. Conclusion. Cervical disc arthroplasty with both the BRYAN and PRESTIGE LP discs not only preserved the motion at the operated level, but also maintained the normal motion at the adjacent levels. Under simulated physiologic loading, the motion patterns of the spine with the BRYAN or PRESTIGE LP disc were very similar and were closer than fusion to the intact motion pattern. An adjacent segment disc replacement is biomechanically favorable to a fusion in the presence of a pre-existing fusion. Level of Evidence: N/A

Biomechanical analysis of the intact and destabilized sheep cervical spine.

Study Design. An in vitro investigation of the biomechanics of the intact and destabilized sheep cervical spine. Objective. To establish the primary and coupled behaviors of the sheep cervical spine, levels C2–C7. Summary of Background Data. Sheep spine models are often used as a precursor to human cadaveric and clinical trials. Several studies have focused on the sheep anatomy and functional spinal unit biomechanics. However, there has not been a comprehensive study of the multilevel sheep cervical spine. Methods. Adult sheep cervical spines (C2–C7) were tested in flexion-extension, lateral bending, and axial rotation, using a 6-df testing apparatus. Moment-rotation curves were generated to understand the entire loading curve. Functional spinal units were tested at various levels of destabilization by sequentially removing the stabilizing structures (i.e., ligaments, facets). Results. The range of motion increased with caudal progression. The average total range of motion was approximately 77°, 130°, and 64° for flexion-extension, lateral bending, and axial rotation, respectively. The neutral zone accounted for a large range of motion during flexion-extension (∼63%) and lateral bending (∼72%). The flexion, extension, and axial rotation motion greatly increased after the removal of the capsular ligaments and facets. The C2–C3 has the largest change in motion during the various stages of destabilization. Conclusion. The sheep cervical spine is extremely flexible, as seen by the large range of motion and neutral zone. The large neutral zone may account for the coupled motion between axial rotation and lateral bending. The facets and capsular ligaments provide significant stability, especially in axial rotation, flexion, and extension.

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.

In Vitro Study of the C2-C7 Sheep Cervical Spine

Due to the limited availability of human cadaveric specimens, animal models are often utilized for in vitro studies of various spinal disorders and surgical techniques. Sheep spines have similar geometry, disc space, and lordosis as compared to humans [1,2]. Several studies have identified the geometrical similarities between the sheep and human spine; however these studies have been limited to quantifying the anatomic dimensions as opposed to the biomechanical responses [2–3]. Although anatomical similarities are important, biomechanical correspondence is imperative to understand the effects of disorders, surgical techniques, and implant designs. Some studies [3–5] have focused on experimental biomechanics of the sheep cervical functional spinal units (FSUs). Szotek and colleagues [1] studied the biomechanics of compression and impure flexion-extension for the C2-C7 intact sheep spine. However, to date, there is no comparison of the sheep spine using pure flexion-extension, lateral bending, or axial rotation moments for multilevel specimen. Therefore, the purpose of this study was to conduct in vitro testing of the intact C2-C7 sheep cervical spine.Copyright

Affect of Attachment Site on Medial Patellofemoral Ligament Reconstruction: A Finite Element Analysis

Bony anatomy, soft tissue restraints, and the dynamic action of the quadriceps all play a role in maintaining patellar stability throughout knee motion. The medial patellofemoral ligament (MPFL) is the main soft tissue restraint to lateral translation of the patella, and helps guide the patella into the trochlear groove during the first 30° of knee flexion [1]. Studies have shown that the MPFL is the most consistently injured anatomical structure after acute lateral patellar dislocation [2]. Due to the high rate of recurrent episodes of instability following conservative management of acute lateral patellar dislocation, a number of bony and soft tissue procedures have been described to restore patellar stability, including MPFL reconstruction [2].Copyright

A Finite Element Analysis of the C2-C7 Sheep Spine

Due to the limited availability of human cadaveric specimens, sheep are often utilized for in vitro studies of various spinal disorders and surgical techniques. Understanding the similarities and differences between the human and sheep spine is crucial for constructing a valuable study and interpreting the results. Several studies have identified the anatomical similarities between the sheep and human spine; however these studies have been limited to quantifying the anatomic dimensions as opposed to the biomechanical responses [1–2]. Although anatomical similarities are important, biomechanical correspondence is imperative for studying the effects of disorders, surgical techniques, and implant designs. Studies by Wilke and colleagues [3] and Clarke et al. [4] have focused on experimental biomechanics of the sheep cervical functional spinal units (FSUs).Copyright