This standard will develop a set of best practices for using finite element analysis (FEA) to determine mechanical performance of spinal fusion cages according to the methods prescribed by ASTM F2077. Spinal fusion (or interbody fusion, IBF) cage geometries will be limited to monoblock cage designs with few confounding features (threads, teeth, and re-entrant corners). Analyses will be limited to static. Device material properties will be limited to homogenous, isotropic, and linear-elastic. Loading modes will be limited to uniaxial compression. These methods are intended to be used for identifying a worst-case specimen within a design family for subsequent fatigue testing. This technique assumes that stress concentrations determined from static FEA are inversely proportional to fatigue life. The practices developed here will form a baseline, and will later be expanded to include the evaluation of more complex geometries and loading scenarios.
Numerical, computational, model
Bench tests for characterizing the mechanical performance of spinal fusion cages can produce inconsistent results. While intra-lab experiments are very repeatable, inter-lab results often display high levels of variability. Differences in test protocols, load fixtures, and interpretation of experimental data can all influence results. This makes it difficult to evaluate the relative performance of spinal fusion cages. Finite element analysis (FEA) may provide a more repeatable alternative to bench testing. However, there are currently no standards or best practices for characterizing the mechanical behavior of spinal fusion cages with FEA. As such, the quality of FEA practices used to characterize the mechanical performance of spinal fusion cages varies widely. An investigation of spinal fusion cage 510(k) submissions from 2013 to 2017 revealed that most finite element models lack the items needed to establish credibility. Moreover, a survey of industry stakeholders indicated that while most companies conduct FEA, most of the modelers do not consult any best practices documents. This lack of repeatability and guidance creates additional burden for industry modelers and government reviewers. Industry stakeholders and government regulators need a consistent method for implementing FEA in the determination of spinal fusion cage mechanical performance.
The title and scope are in draft form and are under development within this ASTM Committee.
Developed by Subcommittee: F04.25
Staff Manager: Kathleen Chalfin
Date Initiated: 06-27-2018
Technical Contact: Jonathan Peck