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Prediction of Anterior Vertebral Body Tethering Outcomes with Patient-Specific FE Modeling

Friday, August 21, 2020

9:00 AM-11:00 AM

BIOMED Master's Thesis Defense
Prediction of Anterior Vertebral Body Tethering Outcomes with Patient-Specific Finite Element (FE) Modeling

Christian D’Andrea, Master’s Candidate
School of Biomedical Engineering, Science and Health Systems
Drexel University

Sriram Balasubramanian, PhD
Associate Professor
School of Biomedical Engineering, Science and Health Systems
Drexel University

Adolescent Idiopathic Scoliosis (AIS) is a 3-D spine and ribcage deformity that develops during the adolescent growth spurt. This condition affects 2-4% of the adolescent population in the United States and can cause detrimental effects in terms of cardiopulmonary function and movement range. When curvature continues to increase in severity despite conservative treatments such as bracing, surgical intervention is required. Posterior spinal fusion is the current standard for severe AIS correction, but this approach uses a rigid construct which suppresses growth after surgery. Anterior vertebral body tethering (AVBT) addresses this limitation through growth friendly correction, where a flexible instrumentation construct provides partial correction through surgery and further correction by altering growth rates within vertebrae.

The challenge faced in AVBT surgical planning is the inability to accurately predict the correction due to post-operative growth which has led to over-correction. Finite element (FE) modeling is a means to simulate behavior of a mechanical system and has been previously utilized in AVBT outcome prediction. However, the current models lack anatomical completeness which sacrifices predictive and analytical capabilities. Therefore, this study sought to bridge the existing gap through AVBT outcome prediction with an anatomically complete FE model.

FE models were created to 1) represent the normative growth patterns of the spine and the region-specific growth of the vertebrae, 2) represent the changes in normative growth behavior that occur under asymmetrical loading in the AIS spine, and 3) apply these principles in simulating AVBT clinical case studies with patient-specific FE models. Through the first goal, both the changes in spine height and in vertebral morphology in the FE model were represented within reported age- and sex- matched ranges. In the second goal, a proof-of-concept simulation of asymmetrical vertebral growth under stress was demonstrated with and without AVBT instrumentation. This illustrated the growth patterns that contribute to either curve progression or curve correction. In the third goal, AVBT surgery and post-operative growth were simulated for three patients in a clinical study.

After one year of post-operative growth, changes in clinical indices were represented to an accuracy within that of human X-Ray measurement. Furthermore, each patient’s FE model produced this post-operative correction through altering vertebral asymmetrical growth. This study illustrates the predictive utility of FE models in surgical planning and prognosis for growth-modulating AIS surgical procedures and allows for further study of optimizing AVBT outcomes.

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