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

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. Deployable Euler spiral connectors (DESCs), 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. Several tests, including finite element analysis (FEA), compression testing, shear testing, and deployment in a cadaver, were performed as initial verification and validation that the concept device performs well under typical testing paradigms used for interbody cages. While further device testing and refinements are necessary prior to clinical use, the present work demonstrates the promise of this approach and highlights the potential of compliant mechanism devices for advancing minimally invasive (MIS) lumbar fusion.