As an engineer, the “bio” portion of biomechanics has presented a monumental challenge. Like no other test specimen, biological specimens are not created nor formed into convenient repeatable test samples. Herein lies the challenge of the field of spine biomechanics. In particular, biomechanical comparisons that provide physicians a valid basis to choose a specific treatment goes to the heart of one of the fundamental objectives of engineering:​ to improve the quality o f life.

In spine biomechanics, the relative motion between one vertebral body in relationship to the adjacent is critical for a number of different reasons. Clinically, issues with patient instability at a motion segment may be an indication o f degenerative disc disease. Biomechanically, what are the treatments that would reduce this instability? In the case in which fusion is desired, i.e., the restriction of vertebral movement through bone growth across the motion segment, the motion should be significantly smaller. In addition, fixation through spinal implants may also result in the same desired near zero displacement.

In each human joint, without exception, six degrees of freedom are allowed. The objective of this work was to design and implement a displacement measurement system which considers all sue degrees of freedom and thus eliminates the need for some of the simplifying assumptions concerning the joint motion in a spinal motion segment during biomechanical testing. A minimum of six displacements must be measured and used as input for a program named 3Dspine and the position of markers must be localized through a stereotactic system. This program then reconstructs the displacement and allows certain parameters to be monitored. The result is a functional 3D analysis program that can be used to analyze any motion between two bodies that are assumed to be rigid.