Towards Improving Computational Modeling of the Lumbar spine - Impact of Material properties and Laminotomy on Spinal Biomechanics

Spinal ligaments play a crucial role in maintaining the mechanical stability of the lumbar spine. These dense, collagenous tissues not only resist excessive motion but also distribute loads between spinal components to protect neural structures. Traditionally, the mechanical response of ligaments has been modeled using linear elastic assumptions, which treat the tissue as having a constant stiffness regardless of loading history. While this simplifies analysis, it fails to capture the time-dependent behaviors, such as creep, stress relaxation, and hysteresis, that are characteristic of biological tissues. Viscoelastic modeling may provide a more physiologically accurate representation by incorporating both elastic and viscous elements, enabling the ligament’s response to evolve with changes in strain rate, duration, and history. However, it is unknown how the inclusion of viscoelastic properties of impacts model validity. This study integrates experimental testing of porcine lumbar ligaments with finite element (FE) simulations to assess the influence of linear elastic and viscoelastic ligament models on spinal biomechanics. Ligament specimens were subjected to tensile testing and stress relaxation protocols, with digital image correlation used to quantify strain. The data were fitted to a transversely isotropic Mooney-Rivlin material model to obtain the viscoelastic material parameters of each ligament and incorporated into an FE model of the lumbar spine. A secondary focus of the investigation was laminotomy, a common decompression surgery involving partial removal of the vertebral lamina. The study simulated varying laminotomy widths and assessed their impact on spinal biomechanics. The results indicate that increasing the width of laminotomy results in increased stress on the remaining bony structures, particularly during axial rotation and flexion. This stress concentration may raise the risk of developing stress fractures, postoperative instability and spondylolysis. Conversely, minimizing the extent of bone removal helps reduce stress in critical areas of the spine, potentially improving patient outcomes and reducing the need for additional stabilization procedures. Findings offer valuable insight for surgeons in planning decompression procedures, counseling patients, and managing postoperative recovery.