From single ligament to multi-ligament injury: a finite element study on the contribution of the posterior ligamentous complex to segmental stability and intervertebral disc stress distribution.

Objective: The posterior ligamentous complex (PLC) plays a crucial role in maintaining lumbar spine stability. PLC injuries have become a key factor in lumbar instability, with the increase in degenerative spinal conditions and surgical interventions. This study aimed to systematically quantify the impact of single and multi-ligament injuries on spinal stability and analyze their effects on lumbar biomechanical indices and intervertebral disc stress distribution.

Methods: Finite element analysis (FEA) and experimental measurements were employed to examine the effects of 12 ligament resection combinations on lumbar range of motion (RoM) and intervertebral disc stress distribution. Detailed statistical analysis, including the Kruskal-Wallis Test, was used to evaluate the significance of observed differences. Functional contributions of individual ligaments and their combinations were analyzed to assess their roles in restricting spinal motion.

Results: The results indicated that ligament resection combinations significantly impacted lumbar biomechanical indices (P = 0.016), with an effect size (η²) of 0.058, reflecting a moderate impact on segmental stability. The interspinous ligament (ISL) demonstrated the most significant role in restricting excessive spinal motion, followed by the ligamentum flavum (LF), while the supraspinous ligament (SSL) and facet joint capsules (FJC) had limited effects. Combined multi-ligament injuries, particularly ISL and LF resection, markedly increased spinal instability and altered intervertebral disc stress distribution. Despite significant stability loss from multi-ligament injuries, intact ligaments provided functional compensation, mitigating instability.

Conclusion: This study revealed the nonlinear cumulative effects of PLC damage on spinal stability, emphasizing the dominant roles of ISL and LF in maintaining biomechanical integrity. The findings provide critical quantitative insights for clinical decision-making, surgical planning, and postoperative rehabilitation strategies, highlighting the importance of preserving intact ligaments to leverage their compensatory capacity in mitigating instability.