Finite Element Study of Two Generations of Lumbar Disc Prostheses

Total disc replacement (TDR) is an emerging technique for addressing degenerated intervertebral discs. However, the first generation of TDR has been associated with the generation of wear debris, which may adversely affect surrounding biological tissues, and they fail to fully replicate the range of motion (ROM) of a healthy intervertebral disc. This study aims to compare two generations of TDRs to determine which more effectively mimics the biomechanical behavior of a biological disc while minimizing associated complications. Four finite element models (healthy L4-L5, Prodisc-L, SB-Charité, and a second-generation TDR) were studied using Ansys under specific loads and moments: 7.5 Nm and 1175 N in flexion, 7.5 Nm and 500 N in extension, 7.8 Nm and 700 N in lateral bending, and 5.5 Nm and 720 N in axial rotation. First-generation TDRs reduce ROM in flexion (-61% for Prodisc-L, -65% for SB-Charité) and in extension (-59.37% and -79%). However, they increase ROM in lateral inclination (+121% and +100%) and in axial rotation (+129.41% and +111.76%). The second-generation TDR shows minimal deviations from the intact model, except in extension. First-generation of disc prostheses do not maintain 100% ROM of an intact intervertebral disc and generate wear debris during operation, potentially compromising surrounding biological tissues. In contrast, second-generation of disc prostheses closely mimic the ROM of an intact disc due to the hyperelastic properties of their core and eliminate wear debris production through to its monobloc design.