Are Ceramic Cages an Option for Lumbar Interbody Fusion? A Comparative Biomechanical Numerical Study

Background: The treatment of severe disc pathologies through lumbar interbody fusion (LIF) involves the insertion of an interbody cage into the degenerated disc space, together with a supporting fixation system. Conventional cage materials, such as Ti6Al4V and PEEK, present several limitations, most notably their non-biodegradability, increasing the risk of cage migration and long-term subsidence (up to 40% incidence). Bioceramics may represent an option while addressing the issue of biodegradability. This study preliminarily investigates the applicability of a commercial bioceramic as an interbody cage material for LIF. Methods: First, an intact L4-L5 functional spine unit (FSU) was validated under both pure moments and combined loading conditions. Subsequently, all surgical steps of the LIF procedure were simulated, followed by postoperative physiological loading to compare the mechanical performance of the ceramic device with standard titanium cages. Two surgical techniques, posterior-LIF (PLIF) and eXtreme-LIF (XLIF), were analyzed. Each simulation assessed the mechanical strength of the interbody cage, the posterior fixation, and the vertebral bone, together with the FSU kinematic. Results: The intact model accurately predicted literature-reported kinematics and intradiscal pressure, and the LIF model reproduced forces on titanium cages consistent with in vitro measurements on human specimens. Both XLIF and PLIF procedures resulted in significant kinematic stabilization of the FSU, with > 70% reduction in range of motion. For PLIF, ceramic cages sustained applied loads with no predicted failure, while XLIF showed minimal interface failure (< 0.6%). Compared with titanium, ceramic cages significantly reduced adjacent vertebral strain, lowering the subsidence risk, without overloading the posterior fixation system. Conclusion: The present study supports the potential of bioceramics as viable materials for interbody cage applications in LIF procedures. Experimental tests and clinical validation should be accompanied to further cage design optimization to enhance the safety margins of this novel bioceramic device and ensure proper clinical effectiveness.