FLEXION-DISTRACTION INJURY OF THE LUMBAR SPINE - INFLUENCE OF LOAD, LOADING RATE, AND VERTEBRAL MINERAL-CONTENT

The biomechanical response of the lumbar spine to combined flexion-she ar loading was determined experimentally The injury model simulated fl exion-distraction trauma to the lumbar spine. Forty-eight lumbar funct ional spinal units (FSUs) were subjected to dynamic loading to injury with six different load types. The reactive forces and moments and res ulting deformity were determined. Static physiologic loading was perfo rmed before and after the injurious loading to assess residual injury. The biomechanical response of FSUs was dependent on the amount of loa d and loading rate. The vertebral bone mineral content explained most of the biologic variation of the results. An osteoporotic or severely degenerated spine will be more easily rendered unstable after trauma w ith lower deformity. Injury at high loading rates will create instabil ity with lower deformity. In vitro experiments should be performed on entire spinal units and with combined loads.