Introduction Osteoporotic vertebral wedge fractures can lead to pain, disability and deformity. Strengthening ('augmenting') fractured vertebrae by injecting cement into them can provide analgesia and enable early mobilisation, but it remains unclear which of two procedures (vertebroplasty or kyphoplasty) is mechanically superior. This cadaveric study compared their ability to restore vertebral shape and function following severe wedge fractures. Methods Pairs of thoracolumbar "motion segments", aged 72•98 years, were overloaded to induce fracture, and then cyclically loaded to create severe wedge deformity. One of each pair underwent vertebroplasty and the other kyphoplasty. The following were measured before and after wedge fracture, after augmentation, and after cyclic loading: compressive stiffness, creep deformation, stress distributions within adjacent intervertebral discs, and vertebral height and shape. The stress distributions quantified intra-discal pressure (lOP) and neural arch load-bearing (FN). Treated vertebrae underwent micro-CT to assess regional cement fill and its relationship to mechanical and morphological outcomes. Results On average, following wedge fracture, FN increased by 58%,!DP fell by 96% and compressive stiffness fell by 44%. Anterior vertebral body height was reduced by 34%, and wedge angle increased from 5.0° to 11.4°. Both procedures were equally effective at restoring IDP, FN and compressive stiffness. Creep deformation was greatest anteriorly, and least posteriorly, but depended little on treatment type or experimental stage. Kyphoplasty restored anterior height loss by 97% (immediately) and by 79% (after creep loading). Values for vertebroplasty (59% and 47% respectively) were significantly less (p