Purpose <p>Lumbar spinal stenosis (LSS), prevalent among the elderly, involves the narrowing of the spinal canal or neural foramen, often causing nerve compression. Understanding the biomechanical effects of postural changes on the ligamentum flavum (LF) and other lumbar structures is crucial for LSS management. This study aimed to investigate the impact of different postures on LF thickness, disc height, and foraminal height to enhance our understanding of LSS pathogenesis.</p> Methods <p>Nine cadaveric lumbar specimens were analyzed for biomechanical changes in LF thickness, intervertebral discs, and foraminal height across flexion, extension, lateral bending, and axial rotation postures. Postural changes were induced by applying joint moments, and specimens were imaged using computed tomography. Three-dimensional models were created to measure the spinal structures during different postures.</p> Results <p>LF thickness increased progressively from the upper to the lower lumbar segments, peaking at L4/L5. Flexion significantly reduced LF thickness at L3/L4 and L4/L5 levels, while lateral bending thickened LF at L1/L2 and thinned it at L4/L5, with no significant difference at the concave and convex sides. Right axial rotation increased LF thickness at L1/L2 and L2/L3. Disc height increased anteriorly during extension and decreased during flexion. Foraminal height decreased during extension at L1/L2, L2/L3, and L3/L4 and increased during flexion at L2/L3, L3/L4, and L4/L5. Lateral bending caused foraminal height changes, with decreases on the concave side and increases on the convex side.</p> Conclusion <p>This study revealed that postural variations affect LF thickness, disc height, and foraminal height, providing insights into LSS biomechanics. These findings may aid in developing improved management strategies for individuals with LSS.</p>