# A novel nanohydroxyapatite/polyamide 66 strut for reducing subsidence after one-level anterior cervical corpectomy and fusion: a finite-element study

## TL;DR

This study introduces a new nanohydroxyapatite/polyamide 66 strut to improve spinal fusion outcomes and reduce subsidence after cervical spine surgery.

## Contribution

A novel n-HA/PA66 strut is proposed and evaluated for its biomechanical performance in cervical spine fusion.

## Key findings

- The new strut showed lower stress concentration at the screw–vertebra interface compared to the old strut.
- The novel strut demonstrated better biomechanical performance under axial pressure and rotational forces.
- Stress distribution at the strut body–endplate interface was more favorable in the new strut design.

## Abstract

The aim of this study is to introduce a novel nanohydroxyapatite/polyamide 66(n-HA/PA66)n strut to improve biomechanical performance and reduce subsidence.

One validated intact and 2 ACCF-simulated C3–C7 cervical spine models were developed (old strut: Group A, new strut: Group B). In the ACCF models, C5 underwent corpectomy and was fixed by an anterior cervical plate. Screw angles were categorized as 1 (0 ) and 2 (45 ) and divided into 4 groups, A1, A2, B1 and B2, for each model. An axial force of 74 N and a moment couple of 1.0 Nm were imposed on the C3 vertebra. The range of motion (ROM) of each segment and the stress distribution on the screw–vertebra interface, strut, and strut–endplate interface were recorded and analysed.

There was no significant difference in ROM between Group A and Group B during bending, extension and rotation under 74 N axial pressure. The stress concentration on the strut body in Group A was higher than that in Group B. The peak stress values at the screw–vertebral interface in Groups A1 and A2 were higher than those in Groups B1 and B2, except for during extension and lateral bending. Under axial pressure, the peak stress values at the strut body–endplate interface during bending, extension and rotation were lower in the A1 and A2 groups than in the B1 and B2 groups. The Group B model showed much higher graft stress than the Group A model.

Based on finite-element analysis, compared with the old strut, the novel strut showed better biomechanical performance at the screw–vertebra interface.