How to select the elastic modulus for cancellous bone in patient-specific continuum models of the spine.

Patient-specific finite element (FE) modelling is a promising technology that is expected to support clinical assessment of the spine in the near future. To allow rapid, robust and economic patient-specific modelling of the whole spine or of large spine segments, it is practicable to consider vertebral cancellous bone in the spine as a continuum material, but the elastic modulus of that continuum material must reflect the quality of the individual vertebral bone. A numerical parametric model of lattice trabecular architecture has been developed for determining the apparent elastic modulus of cancellous bone Ecb in vertebrae. The model inputs were apparent morphological parameters (trabecular thickness TbTh and trabecular separation TbSp) and the bone mineral density (BMD), which can all be measured in vivo, using the spatial resolution of current clinical quantitative computed tomography (QCT) commercial whole-body scanners. The model predicted that Ecb values between 30 and 110 MPa represent normal morphology and BMD of human spinal cancellous bone. The present Ecb to TbTh, TbSp and BMD relationships pave the way for automatic generation of patient-specific continuum FE spine models that consider the individual's osteoporotic or other degenerative condition of cancellous bone.