Heterogeneous porosity design triggered stress reorganization to avoid intervertebral cage subsidence and promote spinal fusion

Abstract

The common phenomenon of cage subsidence after intervertebral fusion may lead to intervertebral foramen stenosis and implantation failure. In this study, a heterogeneous porous cage was designed to trigger the stress reorganization so as to avoid intervertebral cage subsidence and promote spinal fusion. Firstly, finite element analysis (FEA) was used to predict the heterogenous stress distribution on intervertebral discs. Then, a heterogeneous porous structure cage was inspired by the stress reorganization method. Parametrical modeling was employed to customize the porous structure of the cage. Heterogenous Ti6Al4V cage was successfully fabricated via selective laser melting 3D printing. The results from FEA simulation indicated that heterogenous cage with a dense periphery and a porous center may drive the load outward which mimicking the natural stress distribution of spine system. Finally, an animal model between the C3-C4 vertebras of goats was studied to prove the effectiveness of the cage fusion. The histologicaland micro-CT results indicated that the heterogeneous structure may accelerate bone tissue ingrowth so as to promote osteointegration and fusion. Compared with conventional cage, the heterogenous cage may avoid subsidence and this heterogenous structure provide a promising strategy for customized bio-fusion intervertebral cage.