Optimization of nucleus pulposus removal rate in the intervertebral disc during artificial nucleus replacement using lumbar finite element model simulation

A herniated intervertebral disc (HIVD) is a disease caused by the prolapse of the nucleus pulposus of the intervertebral disc due to aging and repeated damage. To treat this, artificial nucleus replacement (ANR) is used to restore the height and flexibility of the reduced intervertebral disc by replacing a portion of the aged nucleus pulposus with an artificial one. However, few studies provide quantitative criteria for partial nucleus pulposus removal. Therefore, through finite element model (FEM) simulation of the lumbar spine (L4-L5), we obtained the optimal location and rate of nucleus pulposus removal and analyzed the movement of the model after ANR in this study. We modeled the FEM in which 60%, 80%, 87%, and 93% of the total nucleus pulposus were replaced by the artificial nucleus pulposus in each of the four directions (left, right, anterior, posterior). Then, a z-axis load of 400N was applied to the model to obtain an axial compression displacement, and a y-axis moment of -6 Nm~+6 Nm was applied to the model to analyze a flexion-extension range of motion (ROM). As a result, regardless of the location of the remaining nucleus pulposus, the compression displacement of the 80% and 87% nucleus pulposus removed model was restored to about 98% of that of the intact model. In addition, the ROM of the 87% nucleus pulposus removed model was restored in 96% of that of the intact model. It is expected that the data obtained through this study can be utilized in digital twin research to predict the prognosis of ANR and to improve surgical techniques.