The Journal of Bone and Joint Surgery, Vol 58, Issue 5 642-652, Copyright © 1976 by Journal of Bone and Joint Surgery, Inc
Mechanical properties of the human thoracic spine as shown by three-dimensional load-displacement curves
MM Panjabi, RA Brand and AA White
The mechanical properties of the human spine are best described by
load-displacement curves which include coupling effects. Three-dimensional
load-displacement curves were obtained for all levels of the human thoracic
spine using fresh cadaver spines in an atmosphere containing 100 per cent
humidity at 22 degrees centigrade to stimulate a physiological environment.
Six forces and six moments were applied, one at a time, to the center of
the upper vertebra while its subadjacent fellow was fixed. Assuming
sagittal plane symmetry, vertebral displacement was measured in
three-dimensional space and load-displacement curves were plotted for the
main as well as the coupled motions. The thirty-six curves necessary to
define the mechanical characteristics of each motion segment completely
were determined for all eleven thoracic levels. The curves showed that all
the thoracic spine is a complex three-dimensional structure with coupled
motion characteristics. Axial forces (compression/tension) resulted in
significant horizontal displacements. Spine motion segments were more
flexible in flexion than in extension. The spine was found to be least
flexible during axial compression.