Buckling of osteoporotic lumbar: finite element analysis

Abstract

Contribution of osteoporotic degradation to instability of lumbar spine is investigated by the finite element method. The aim of this work is to assess the biomechanical response of the osteoporotic L3 vertebrae under axial compression loading. The human lumbar spine segment comprising L2-L4 is considered. The anatomic shape of the patient-specific image-based geometry of lumbar vertebra is used for the three-dimensional finite element model. The cortical skin of vertebra id modelled by the shell, while cancellous tissue by the volume elements. The weak intervertebral discs are modelled as 3D composite. Three models including healthy and two trabecular bone osteoporotic degeneration cases are analyzed. The first case is restricted to osteoporotic degradation cancellous bone tissue as it is used in common praxis while the second case reflects limit situation when trabecular rarefaction occurs near the outer cortical shell. Numerical results of the non-linear finite element analysis showed that osteoporotic degradation is potentially suspicious for instability. The rarefication of cancellous bones yields to local buckling of vertebral wall essentially reducing load-bearing capacity, which has to be considered in such extreme situations. Consequently, the vertebra loses load-bearing capacity even when the strength limit is not reached. 3D finite element models were used. The aim of this work is to assess the biomechanical response, or load transfer response, between osteoporotic L3 vertebrae under compression loading. For this purpose, image-based, heterogeneous, three-dimensional, patient-specific finite element models of the lumbar vertebrae L3 for osteoporotic subjects were created. The finite element analysis has shown that local vertebral damage, such as empty spaces in vertebral bone, give rise to vertebral wall point’s horizontal displacement increase. Consequently, the vertebra loses load-bearing capacity even when the strength limit is not reached.