Biomechanical analysis of a novel height-adjustable nano-hydroxyapatite/polyamide-66 vertebral body: a finite element study

BACKGROUND: To compare the biomechanical properties of a novel height-adjustable nano-hydroxyapatite/polyamide-66 vertebral body (HAVB) with the titanium mesh cage (TMC) and artificial vertebral body (AVB), and evaluate its biomechanical efficacy in spinal stability reconstruction. METHODS: A 3D nonliner FE model of the intact L1-sacrum was established and validated. Three FE models which instrumented HAVB, TMC, and AVB were constructed for surgical simulation. A pure moment of 7.5 Nm and a 400-N preload were applied to the three FE models in 3D motion. The peak von Mises stress upon each prosthesis and the interfaced endplate was recorded for analysis. In addition, the overall and intersegmental range of motion (ROM) of each model was investigated to assess the efficacy of each model in spinal stability reconstruction. RESULTS: AVB had the greatest stress concentration compared with TMC and HAVB in all motions (25.6–101.8 times of HAVB, 0.8–8.1 times of TMC). The peak stress on HAVB was 3.1–10.3% of TMC and 1.6–3.9% of AVB. The maximum stress values on L2 caudal and L4 cranial endplates are different between the three FE models: 0.9–1.9, 1.3–12.1, and 31.3–117.9 times of the intact model on L2 caudal endplates and 0.9–3.5, 7.2–31.5, and 10.3–56.4 times of the intact model on L4 cranial endplates in HAVB, TMC, and AVB, respectively, while the overall and segmental ROM reduction was similar between the three models, with AVB providing a relatively higher ROM reduction in all loading conditions (88.1–84.7% of intact model for overall ROM and 69.5–82.1% for L1/2, 87.0–91.7% for L2/4, and 71.1–87.2% for L4/5, respectively). CONCLUSIONS: HAVB had similar biomechanical efficacy in spinal stability reconstruction as compared with TMC and AVB. The material used and the anatomic design of HAVB can help avoid stress concentration and the stress shielding effect, thus greatly reducing the implant-associated complications. HAVB exhibited some advantageous biomechanical properties over TMC and AVB and may prove to be a potentially viable option for spinal stability reconstruction. Further in vivo and vitro studies are still required to validate our findings and conclusions.