Leveraging Compliance to Design a Minimally Invasive, Expandable Interbody Cage Capable of Customized Anatomical Fit for Spinal Fusion Surgery

Abstract

As spinal fusion surgery continues to transition to less invasive techniques, there remains an unmet need for ever smaller and more complex interbody cages to meet the unique needs of this difficult surgery. This work focuses on the hypothesis that this need can be met using the inherent advantages of compliant mechanisms in a way no previous device has. Deployable Euler Spiral Connectors optimized using a gradient based optimization algorithm were used as the foundation for a device that can stow to a very small size for device insertion then bilaterally deploy to a substantially larger device footprint. Additionally, a continuously adjustable lordotic angle was achieved using the same device so as to result in a customized anatomical fit while potentially reducing hospital inventory requirements. Several tests including finite element analysis, compression testing, shear testing, and deployment in a cadaver were performed as initial verification and validation that the concept device performs reasonably well under typical testing paradigms used for interbody cages.