Augmentation of mechanical properties in osteoporotic vertebral bones - a biomechanical investigation of vertebroplasty efficacy with different bone cements

Recent clinical trials have reported favorable early results for transpedic ular vertebral cement reinforcement of osteoporotic vertebral insufficienci es. There is, however, a lack of basic data on the application, safety and biomechanical efficacy: of materials such as polymethylmethacrylate (PMMA) and calciumphospate: (CaP) cements. The present study analyzed 33 vertebral pairs from five human cadaver spines. Thirty-nine vertebrae were osteoporo tic (bone mineral density <0.75 g/cm(2)), 27 showed nearly normal values, T he cranial vertebra of each Fair was augmented with either PMMA (Palacos E- Flow) or experimental brushite cement (EBC), with the caudal vertebra as a control, PMMA and EBC were easy to inject, and vertebral fillings of 20-50% were achieved. The maximal possible filling was inversely correlated to th e bone mineral density (BMD) values. Cement extrusion into the spinal canal was observed in 12% of cases. All specimens were subjected to axial compre ssion tests in a displacement-controlled made. From load-displacement curve s, the stiffness, S, and the maximal force before failure? F-max. were dete rmined. Compared with the native control vertebrae, a statistically signifi cant increase in vertebral stiffness and F-max was observed by the augmenta tion. With PMMA the stiffness increased by 174% (P=0.001) and F-max by 195% (P=0.001); the col responding augmentation with EBC was 120% (P=0.03) and 113% (P=0.002). The lower the initial BMD, the more pronounced was the augm entation effect, Both PMMA and EBC augmentation reliably and significantly raised the stiffness and maximal tolerable force until failure in osteoporo tic vertebral bodies. In nonporotic specimens. no significant increase was achieved.