Biomechanical Effects of a Tethering Device in Interbody Fusion During Four Movements: A Finite Element Study

Adjacent Segment Disease (ASD) is the complication occurring after Posterior Lumbar Interbody Fusion (PLIF) surgery due to increased mechanical stress at adjacent unfused segments. Tethering techniques have been studied to mitigate the risk of ASD by adjusting the spinal load distribution. This study investigates the biomechanical effects of tethering with Finite Element Analysis (FEA), using a validated L1-L5 spine finite element model focusing on Intervertebral Disc (IVD) pressure and Range of Motion (ROM). The model was applied in four movement directions (Flexion, Extension, Lateral bending, Axial rotation) with tethering applied at the spinous process under two pretension forces (25 N and 50 N). The results showed that tethering reduces IVD stress in flexion, with 25 N pretension gives 13.1% reduction compared to the PLIF-only model. However, tethering also increases stress in extension and lateral bending due to adjusted posterior load distribution. In axial rotation, tethering reduced IVD stress to levels comparable to the intact spine, suggesting potential biomechanical benefits with optimal tension. These findings highlight the effects of tethering as a technique for ASD prevention, though further optimization of tensioning strategies is necessary for clinical applications.