Analog studies of forces in the human spine: Mechanical properties and motion segment behavior

This paper considers the construction and behavior of a mathematical model for the study of the force systems acting in the spine. The assembly of geometric and stiffness data for a model of the isolated ligamentous thoraco-lumbar vertebral column is described. Through a series of trials, the force-deformation properties of many individual elements of cadaver spines were incorporated so that the overall behavior of the model motion segments matches that of cadaver motion segments. The detailed behavior of two motion segments, T8 T9 and L3 L4 , has been studied with the model. The results indicate that (1) the ligaments and facet joints play an important role in carrying loads, especially in bending and torsion; (2) motion coupling is a function of segment orientation as well as of the intrinsic kinematic characteristics of a segment and (3) during normal motions of the column, geometric nonlinearities are significant. Tables of representative mechanical properties and load responses of the spine are given.