Experimental determination of spinal motion segment behavior.

The mechanical behavior of the human spine is complex. Most of the studies in the past have predominantly dealt with axial compression. Some attempts have been made to study spinal behavior resulting from the application of other types of loads. However, coupled motions have not been documented. In the present discussion we have attempted to develop a system that makes it possible to determine the complete elastic behavior of the spine and to present some results of three dimensional studies, including the coupling effects. Some of the conclusions are as follows: 1. The mechanical behavior of the spinal motion segments can be documented by application of 12 physiologic loads to the upper vertebra and measuring the resulting six components of the three dimensional motion. 2. Each physiologic load (a force or a moment) produces one main motion and five coupled motions. 3. Seventy-two load displacement curves are required for a complete description of the elastic behavior of a single motion segment.