Biomechanical behavior of a hydrogel-based TDR device

Degenerative disc disease is one of the most common diseases resulting from inflammation and instability around the affected spinal disc. Total disc replacement (TDR) is one non-fusion technique emerging as potential solutions to this condition, which can be used to restore normal motion in the spine. Although the first generation TDR devices have reasonable clinical results, similar to fusion, but several concerns in the current technologies are the inability to provide adequate shock absorption capability and time-dependent biomechanical behaviors. In order to improve this problem, second generation TDR devices incorporate more properties of a natural disc. Therefore, the objective of this study is to develop a novel biomimetic TDR device, and to demonstrate scientifically whether its biomechanical behavior is similar to that of a natural disc. Three-dimensional finite element (FE) models of a lumbar spinal motion segment (L4-5) with implants including Charité, Maverick, and the hydrogel-based TDR devices were created. With these models, the three different TDR design concepts were compared with respect to their ability to mimic the behavior of a natural disc. The analysis results indicate that the hydrogel-based TDR device could maintain the ROM well compared to that of a natural disc. However, the model with the novel TDR device predicted a marked increase of facet joint forces due to the relatively low rotational stiffness, especially in lateral bending. Although many steps are still necessary before the hydrogel-based TDR device can be used in clinical surgery to relieve back and leg pain associated with DDD. The results provide further insight into the biomechanical behavior of this novel TDR device under comparable physiologic loading conditions, and indicate that it is a feasible and promising approach.