Modular Cage-Type Prosthetic Construction for Lumbar Intervertebral Reconstruction: A Computer-Aided Design-Based Geometric Design and Finite Element Analysis Study.

Background Lumbar interbody fusion (LIF) has become one of the most common surgical treatments for both degenerative and traumatic spinal disorders. Also, advances made in computer-aided design (CAD) and finite element (FE) modeling are creating new ways to test alternate designs and determine how they will initially behave mechanically before being tested experimentally. Objective We aim to create and complete a preliminary biomechanical evaluation of a new modular cage-like prosthetic construct for lumbar intervertebral reconstruction using computer-aided design (CAD) and finite element analysis (FEA). Methods A modular interbody prosthesis concept was created utilizing CAD with an emphasis on a stacked lamellar design and anatomically shaped contact surfaces at each endplate, and a center screw-based lock. Two different sizes of the implant were created to mimic compact and expanded constructs. FEA simulations were completed to examine stress distribution, displacement, safety factor, and load transfer characteristics of the implant under static compressive loading. Additionally, a simplified lumbar spine-cage assembly model was created to simulate implant performance in an anatomical environment. Results Both size configurations remained structurally intact under static compressive loading. Under standardized material, loading, contact, and meshing conditions, the 8 mm construct demonstrated a lower maximum von Mises stress than the 18 mm configuration (39.08 MPa versus 87.54 MPa), reduced global displacement (0.067 mm versus 0.122 mm), and a higher minimum safety factor (2.56 versus 1.14). The 8 mm configuration exhibited a maximum first principal stress of 55.46 MPa and a minimum third principal stress of -36.26 MPa. In the lumbar spine-cage assembly model, peak implant stress was lower than in the isolated expanded cage model, whereas global displacement increased, indicating redistribution of the applied load through the surrounding vertebral structures. Conclusion This proposed modular cage-like prosthetic construct demonstrated configuration-dependent mechanical properties, which enabled controlled variation in intervertebral height while maintaining the same footprint of the implant. An increase in construct height was shown to be associated with increases in localized mechanical demands. Overall, these preliminary computational results suggest the need for continued development of this modular design and additional testing via standardized biomechanical testing, experimental validation, and subsequent clinical evaluation.