Reducing Adjacent Vertebral Stress by Modifying Mechanical Properties of Bone Cement by Addition of Bone Filler in Vertebroplasty- a Biomechanical Study in Porcine Model

Percutaneous vertebroplasty is an effective treatment for painful vertebral fractures in the presence of osteoporosis. Vertebral body fractures are among the most common fractures associated with osteoporosis. Compression fractures of the osteoporotic spine represent an important indication for vertebroplasty. The most widely used bone substitute material for vertebroplasty is polymethylmethacrylate (PMMA), which has significant higher stiffness than osteoporotic vertebral cancellous bone. The use of polymethylmethacrylate (PMMA) cement to reinforce fragile or broken vertebral bodies leads to extensive bone stiffening. While vertebroplasty greatly increases the failure strength of augmented vertebrae, a significantly increased risk of adjacent vertebral body fractures is always found in clinical follow-up. Rigid cement augmentation is considered to facilitate the subsequent collapse of the adjacent vertebrae. In our pilot study, modified bone cement with lower modulus was achieved by addition of bone filler. Our preliminary results indicated that the addition of bone filler resulted in an increase of porosity and reduction of stiffness, which made the modified bone cement with mechanical properties more closed to human cancellous bone. Although the modified bone cement with lower modulus can be achieved by addition of bone filler, previous study addressing the application of such low-modulus bone cement in vertebroplasty is lacking. We propose to perform this study within three years. Low-modulus PMMA will be prepared by adding different content of polysebacic acid. Subsequently, both in vitro experiments and finite element analysis will be conducted to evaluate whether the failure of adjacent vertebral bodies in augmented functional spine unit (FSU) can be avoided using the modified low-modulus bone cement. Previous literature indicating that demineralizing process is useful for producing a vertebra that has mechanical properties consistent with osteoporosis in humans (Akbay et al., Eur Spine J, 17:468-473, 2008). Demineralized porcine FSUs model will be used to assess the efficacy of low-modulus PMMA in vertebroplasty. The contents of this three-year study are summarized as follows: A. The first-year study: Evaluation of low-modulus PMMA in vertebroplasty (Static test) Commercially available PMMA cement mixed with a polysebacic acid solution will be prepared to achieve the modified cement with lower modulus. Vertebroplasty with commercial or low-modulus bone cement using demineralized porcine FSUs model will be conducted. With use of MTS testing machine, static mechanical tests including axial compression, axial torsion, flexion, extension and lateral bending will be performed to evaluate the efficacy of low-modulus PMMA to avoid the failure of adjacent vertebral bodies in vertebroplasty. B. The second-year study: Evaluation of low-modulus PMMA in vertebroplasty (Dynamic test) Cyclic dynamic tests for demineralized porcine FSUs model treated with commercial or low-modulus bone cement will be performed with above-mentioned loading modes. The failure mechanism and longevity of the FSUs model treated with commercial or low-modulus bone cement under various dynamic loading modes will be examined. C. The third-year study: Evaluation of low-modulus PMMA in vertebroplasty (Finite element analysis) Finite element analysis from CT scan images will be conducted to investigate the biomechanical performance of the FSUs model treated with commercial or low-modulus bone cement. Stress distributions of facet joint, disc and bone/cement interface, which can not be obtained from mechanical tests will be determined. FEM Results will be compared and validated by those adopted from mechanical tests

Project ID:PC10107-0354
External Project ID:NSC101-2314-B182A-114