Computer modelling and stress analysis of the lumbar spine

Two three-dimensional models of the fourth and fifth vertebrae were developed to clarify the mechanical causes of low back pain. The lumbar structures produced allowed the simulation, by the performance of finite element analysis, of different situations not normally achievable by experimentation. The simulations yielded data on the stress distribution inside the vertebrae and the amount of deformation that takes place.

Models of the vertebrae were reconstructed by transferring data points to the software package I-DEAS Master Series™. The results show large stress concentrations were found in the superior and inferior facet region and on the central surfaces of the vertebral body. Higher stress concentrations were also found in the cortical shell of the vertebrae. Whilst it was observed that the cancellous core was absorbing some of the compressive loading. The study indicated that the vertebrae act similar to man-made sandwich materials, where the outer hard cortical bone has the ability to resist indentation and abrasion, while the cancellous core is tough and has the ability to absorb energy. With mechanical loading playing a central role in many low back disorders, even when there is no history of trauma, and when degeneration is evident. This present study provides a strong rationale for use of this modelling method as a research tool to assist the clinician in many ways: by indicating how to avoid overloading spinal structures, by assisting diagnosis and the development of surgical techniques.