Verification, Validation, and Uncertainty Quantification of Spinal Rod Computational Models Under Three-Point Bending

Abstract

Verification, validation, and uncertainty quantification (VVUQ) can increase confidence in computational models by providing evidence that a model accurately represents the intended reality of interest. However, there are currently few examples demonstrating the application of VVUQ best practices for medical devices. Therefore, the objectives of this study were to understand the reproducibility and repeatability of experimental testing and finite element analysis (FEA), perform VVUQ activities that guide the development and refinement of a finite element model, and document best practices for future research. This study focused on experiments and simulations of three-point bend testing, which is a fundamental element of a hierarchical validation study of medical devices (e.g., spinal rod-screw systems). Experimental three-point bend testing was performed at two laboratories using medical-grade titanium (Ti-6Al-4V) spinal rods. FEA replicating the experimental test was performed by four independent institutions. Validation activities included comparing differences in mechanical properties between FEA and experimental results, where less than 10% difference was observed for all quantities of interest. Computational model uncertainties due to modeling assumptions and model input parameters were estimated using the sensitivity coefficient method. An importance factor analysis showed that rod diameter was the parameter driving uncertainty in the initial elastic region, while the material model is the primary contributor beyond this point. These results provide a proof of concept in the use of VVUQ for the use of FEA for medical device applications.