Topological optimization design and biomechanical analysis of a novel titanium-PEEK multilayer cage in ACDF surgery: a finite element study

Anterior cervical discectomy and fusion is the gold standard for the treatment of cervical spondylosis, with the cage playing a crucial role in maintaining intervertebral height and promoting bone fusion. However, cages made from single materials, such as polyetheretherketone (PEEK) or titanium alloys, often suffer from limitations like low fusion rates and high risks of subsidence. This study aims to design a multilayer cervical cage optimized through topological optimization, featuring a titanium alloy outer layer and a PEEK inner layer, combining the advantages of both materials to improve fusion rates and reduce the risk of subsidence. A finite element model of the C3-C7 cervical spine was developed, with a simplified ROI-C cage implanted at the C5-C6 segment for topological optimization. The multilayer cage was then redesigned based on the topological optimization result, and its biomechanical performance was compared with that of PEEK and titanium alloy cages. The results showed that there were no significant differences in postoperative cervical range of motion among the three types of cages. The facet joint force of the surgical segment significantly decreased in all models, with the titanium alloy cage model showing the greatest decrease and the PEEK cage model showing the least. The stress distribution at the contact interface between the titanium alloy cage and the vertebral body was the most concentrated, while it was the most uniform in the PEEK cage. In conclusion, the multilayer cage combines the advantages of both titanium alloy and PEEK, ensuring postoperative vertebral stability while reducing stress concentration at the contact interface with the vertebral body. This novel multilayer cage offers a new perspective on the selection of cages in clinical practice.