Biomechanical analysis of retroperitoneal 360° anterior lumbar interbody hybrid stabilization constructs for degenerative conditions: A finite element investigation.

Background: Segmental fusion utilizing interbody cages and pedicle screw fixation (PSF) remains the predominant surgical intervention for managing chronic low back pain. However, the biomechanical efficacy of combining anterior interbody cages with hybrid stabilization techniques, particularly in the context of retroperitoneal 360° anterior lumbar interbody fusion (ALIF) is still debated. Hybrid constructs using flexible pedicle-based systems aim to preserve motion and reduce adjacent segment degeneration (ASD), but their biomechanical performance remains insufficiently explored. This study investigates the biomechanical behavior of retroperitoneal ALIF combined with various hybrid stabilization systems for treating disc degeneration, degenerative spondylolisthesis, degenerative scoliosis, or instability. Methods: A validated, non-linear finite element (FE) model of the lumbosacral spine (L2-S1) was developed to simulate and compare the biomechanics of four hybrid stabilization systems combined with interbody cages. The motion of the whole spine was analyzed and the biomechanical environment of the adjacent segments to the operated one was studied. Moreover, the risk of subsidence of the cages was qualitatively evaluated across different configurations. Results: Supplementary fixation at the "topping off" level reduced overall spinal range of motion but led to increased stress at adjacent segments, potentially contributing to adjacent segment disease (ASD) due to the overload. In contrast, interbody cages allowed controlled relative movement, attenuating the impact on adjacent disc health. However, all hybrid systems produced similar contact pressures at the endplates, approaching subsidence risk thresholds. Conclusions: Minimally invasive posterior intervertebral cage insertion, whether combined with hybrid constructs or traditional fusion fixators, significantly influences lumbar biomechanics. Retroperitoneal 360° ALIF combined with hybrid stabilization significantly alters spinal biomechanics. While hybrid systems may offer advantages in preserving motion and reducing adjacent segment stress, they also present a potential compromise in terms of fusion stability and increased risk of cage subsidence. Optimal surgical outcomes will require careful consideration of trade-offs between mobility preservation, long-term stability, and ASD prevention.