The inferior boundary condition of a continuous cantilever beam model of the human spine.

The continuous cantilever beam model of the human spine usually assumes that the beam tangent at the inferior end of the structure is exactly perpendicular to the surface in which it is built into. The model used in this paper allows for realistic imperfections in the beam so that a small non-zero rotation is allowed at its inferior end. Such a model is used to investigate the lateral deformation of the muscle-relaxed spine as it supports asymmetrical loads in the frontal plane. By comparing the model deformations with previously published results, it was easily seen how such imperfections can effect the solution quantitatively. This was found to be especially true when the model was used to estimate the gross flexural rigidity of the spine in the frontal plane. It could also explain why some spines are more prone to lateral curvature and instability than others. Considering the importance of such a parameter when used in the continuous model, an investigation into the true nature of the inferior model boundary condition could be warranted.