Topology optimisation of spinal interbody cage for reducing stress shielding effect

Abstract

The stress shielding effect is an event in which the replacement implant limits the load transferred to bone and the ineffective stress in the vertebrae causes bony growth to cease. In the present study, a 3D finite element L4–L5 model was developed and subjected to a 1200 N compression preload. Five groups of muscle forces were applied on L4 under flexion–extension, lateral bending and axial rotation. Topology optimisation was employed for reducing the stress shielding effect by removing the ineffective material from the design domain. The optimised design was designed with polyaryletheretherketone (PEEK) titanium and cortical materials to encounter the shielding response. The stress responses show that the new design increased the stress magnitude by at least 17.10, 18.11 and 18.43% in 4 Nm of flexion–extension, lateral bending and axial rotation, respectively. In conclusion, the material factor did not significantly alter the stress magnitude, but volume was the key factor in reducing the stress shielding effect.

Keywords:

• topology optimisation
• stress shielding
• finite element analysis
• lumbar segment
• interbody cage

Acknowledgements

The authors are deeply indebted to Professor Hideyuki Azegami and his research group for providing the geometry data of the spinal segment. Acknowledgement is also extended to Associate Professor Mohd Hamdi bin Shukor who allowed the authors to utilise the Pro-e software in the University of Malaya.