Biomechanical evaluation of PMMA to compliant hydrogels as vertebral augmentation materials within the lumbar vertebrae: an in-silico study

Abstract Purpose Osteoporosis is the most common metabolic bone disorder worldwide and causes a fracture approximately every three seconds. Osteoporotic vertebral fractures (OVFs) are its most frequent complication, often triggering additional fragility fractures that impair mobility and shorten life expectancy. Standard treatments, including vertebroplasty and balloon kyphoplasty, stabilize OVFs using polymethylmethacrylate (PMMA) bone cement. However, PMMA creates a stiffness mismatch with native bone, potentially disrupting normal spinal biomechanics. Recently developed hydrogels with tuneable mechanical and biological properties have emerged as promising alternatives, offering stabilization while supporting natural bone regeneration. Currently, no in-silico studies evaluate how these hydrogel materials influence vertebral biomechanics. This study examines stress distribution in lumbar vertebrae using PMMA versus adjustable-stiffness hydrogels under physiological loading. Methods Finite element (FE) models of the L2-L4 vertebrae were created from T2 weighted MRI images with 6 different motions simulated (Flexion, Lateral Flexion, Compression, Lateral Bending, Extension and Rotation) when considered healthy, osteoporotic, osteoporotic treated with PMMA at two volumes and a tuneable hydrogel of variable stiffness at two volumes. Percentage volume plots were then extracted to assess the volume of elements exhibiting stresses at biologically relevant levels. Results Our FEA results show that higher stresses are observed in the cortical shell for osteoporotic cases when compared to healthy cases. Furthermore, when PMMA is used as the stabilizing agent for osteoporotic cases, this increases again. When compared to tuneable stiffness hydrogels simulations, the hydrogel of stiffness in the MPa range showed load transfer into the gel and reduced stresses in adjacent vertebrae. These observations agree with what is observed through our percent volume of stresses plots. Conclusion FEA simulations of the lumbar spine can provide critical insights into the mechanical implications of different diseased pathologies, treatment options and aid in the development of new medical treatments for OVFs.