Biomechanical Investigation of Lumbar Interbody Fusion Supplemented with Topping-off Instrumentation Using Different Dynamic Stabilization Devices. Issue 24 (15th December 2021) - Fan, Wei
Abstract : A normal finite element model of human lumbosacral spine was modified to simulate interbody fusion with topping-off instrumentation using pedicle-based dynamic stabilization system (PBDSS) or interspinous process spacer (ISP). Biomechanical effects of the PBDSS-based and ISP-based topping-off devices on the transition segment and its supra-adjacent segment were compared. Abstract : Study Design: A biomechanical comparison study using finite element method. Objective: The aim of this study was to investigate effects of different dynamic stabilization devices, including pedicle-based dynamic stabilization system (PBDSS) and interspinous process spacer (ISP), used for topping-off implants on biomechanical responses of human spine after lumbar interbody fusion. Summary of Background Data: Topping-off stabilization technique has been proposed to prevent adjacent segment degeneration following lumbar spine fusion. PBDSS and ISP are the most used dynamic stabilizers for topping-off instrumentation. However, biomechanical differences between them still remain unclear. Methods: A validated, normal FE model of human lumbosacral spine was employed. Based on this model, rigid fusion at L4–L5 and moderately disc degeneration at L3–L4 were simulated and used as a comparison baseline. Subsequently, Bioflex and DIAM systems were instrumented at L3–L4 segment to construct PBDSS-based and ISP-based topping-off models. Biomechanical responses of the models to bending moments and vertical vibrational excitation were computed using FE static and random response analyses, respectively. Results: Results from static analysis showed that at L3–L4, the response parameters including annulus stress and range of motion were decreased by 41.6% to 85.2% for PBDSS-based model and by 6.3% to 67% for ISP-based model compared with rigid fusion model. At L2–L3, these parameters were lower in ISP-based model than in PBDSS-based model. Results from random response analysis showed that topping-off instrumentation increased resonant frequency of spine system but decreased dynamic response of annulus stress at L3–L4. PBDSS-based model generated lower dynamic stress than ISP-based model at L3–L4, but the dynamic stress was higher at L2–L3 for PBDSSbased model. Conclusion: Under static and vibration loadings, the PBDSSbased topping-off device (Bioflex) provided a better protection for transition segment, and likelihood of degeneration of supraadjacent segment might be relatively lower when using the ISPbased topping-off device (DIAM). Level of Evidence: 5