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

Guanghui Chen,Guangjian Bai,Jing Wang,Ting Wang,Baoquan Xin,Tianqi Fan,Tielong Liu,Mengchen Yin,Jianru Xiao

doi:10.1186/s13018-019-1432-2

Abstract

BackgroundTo 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.MethodsA 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.ResultsAVB 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).ConclusionsHAVB 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.

Highlights

To compare the biomechanical properties of a novel height-adjustable nano-hydroxyapatite/polyamide66 vertebral body (HAVB) with the titanium mesh cage (TMC) and artificial vertebral body (AVB), and evaluate its biomechanical efficacy in spinal stability reconstruction
The FEM consists of the cortical bone, cancellous bone, endplates, intervertebral discs, articular cartilage, and seven ligamentous systems including the anterior longitudinal ligament (ALL), posterior longitudinal ligament (PLL), ligamentous flavum (LF), capsular ligaments (CL), intertransverse ligaments (ITL), interspinous ligaments (ISL), and supraspinous ligaments (SSL) (Fig. 1a, b)
Validation of the intact FEM The range of motion (ROM) data of L2–3, L3–4, and L4–5 were obtained and compared with the results of Shim et al from a cadaveric biomechanical study (Table 2). This intact FEM was confirmed to be valid, and the calculated ROM at each intervertebral segment was within ± 1° of the ROM values presented in Shim et al.’s [32] study in all motions (Additional file 1: Figure S1)

Summary

Introduction

To compare the biomechanical properties of a novel height-adjustable nano-hydroxyapatite/polyamide vertebral body (HAVB) with the titanium mesh cage (TMC) and artificial vertebral body (AVB), and evaluate its biomechanical efficacy in spinal stability reconstruction. Titanium mesh cages (TMC) and artificial vertebral body (AVB) such as the VLIFT cage made of metal alloy material have been used widely for their good mechanical properties [10,11,12,13]. Some in vivo and in vitro studies have compared the biomechanical properties of the TMC and AVB systems and found no significant difference between them [16, 17], few studies have addressed the mechanisms underlying these implant-associated complications, and there is little knowledge about the stress acting inside these prostheses. To the best of our knowledge, no study has reported the use of FEM analysis to investigate the biomechanical properties of these two prostheses

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