Mathematical models of the human spine structure are useful in predicting biomechanical behaviour of the spine where actual experiments may never be performed. These models, to be valid, should be based upon experimentally determined mechanical properties of the spine.

Three dimensional flexibility and stiffness properties, including the coupling effects, were determined for all levels of the human thoracic spine. Fresh cadaver spines were used in a 100% humid atmosphere at 22°C to preserve physiological environment. Bottom vertebra of a two vertebrae construct was fixed. Twelve forces and moments, one at a time, were applied to the top vertebra. Vertebral displacement was accurately measured in three dimensional space. Load displacement curves for the main as well as the coupled motions were plotted. Flexibility and stiffness matrices were calculated for the center of the vertebral body. Values for the matrix coefficients, the load-displacement diagrams and the variation of the mechanical properties with the spine level are presented.