Finite element analysis of the cervical spine: a material property sensitivity study

Objective. The study determined the effect of variations in the material pr operties of the cervical spinal components on the output of the finite elem ent analysis (external and internal responses of the cervical spine) under physiologic load vectors. Design. A three-dimensional (3D) anatomically accurate finite element model comprising of the C4-C5-C6 cervical spine unit including the three vertebr ae, two interconnecting intervertebral discs, and the anterior and posterio r ligament complex is used. Background. The effect of material property variations of spinal components on the human lumbar spine biomechanics is extensively studied. However, a similar investigation of the cervical spine is lacking. Methods. Parametric studies on the variations in the material properties of all the cervical spine components including the cortical shell, cancellous core, endplates, intervertebral disc, posterior elements and ligaments wer e conducted by exercising the 3D finite element model under flexion, extens ion, lateral bending and axial torsion loading modes. Low, basic and high m aterial property cases for each of the six components under all the four ph ysiologic loading modes were considered in the finite element analysis. A t otal of 432 results were evaluated to analyze the external angular rotation , and the internal stresses in the middle vertebral body, the superior and inferior endplates and the two intervertebral discs. Results. Variations in the material properties of the different cervical sp inal components produced dissimilar changes in the external and internal re sponses. Variations in the material properties of the cancellous core, cort ical shell, endplates and posterior element structures representing the har d tissues did not affect the external angular motion, and the internal stre sses of the inferior and superior intervertebral discs under all four loadi ng modes. In contrast, variations in the material properties of the interve rtebral disc and ligament structures representing the soft tissues signific antly altered the angular motion, and the stresses in the inferior and supe rior intervertebral discs of the cervical spine. Conclusion. The material properties of the soft tissue structures have a pr eponderant effect on the external and internal responses of the cervical sp ine compared with the changes in the material properties of the hard tissue structures.