The development of replacement intervertebral discs has recently received significant attention in the new product arena. Presently, ASTM International is considering a standard for the evaluation of artificial discs. The purpose of this study was to evaluate human functional spinal units (FSUs) and intervertebral discs using the methods and equipment in the proposed standard and then to compare the results with existing literature.

FSUs and intervertebral discs were tested in axial rotation, anterior and posterior compressive shear, and axial compression. The stiffness values of the intervertebral discs were 1.8 ± 1.1 N. m/° in axial rotation, 368.2 ± 98.6 N/mm in anterior compressive shear, 483.5 ± 62.9 N/mm in posterior compressive shear, and 1287.5 ± 271.3 N/mm in axial compression. These results are reasonable in comparison with the existing literature but there are notable differences. We conclude that the mechanical properties of the intervertebral disc are not sufficiently defined and further testing is warranted.