Objective   To introduce a new fracture experimental model to evaluate the effects of different kinds of internal fixation devices on spinal stability.  Methods   Twelve fresh calf spines from L1 to L5 were collected

and then wedge osteotomy was performed on the 1/3 anterior body of L3 vertebrae. Then drop weight technique and incremental trauma approach was used to produce burst fracture. Ranges of 3 dimensional movements and stiffness of segment L1 to L5 were measured with a spinal three motion test device (Eagle-4

Motion Analysis) before and after trauma.  Results  In the course of testing

the fractural model was restored to normal position after unloading. The range of movement and stiffness of the segments are 9.50±0.81° and 0.42±0.04 Nm/°on flexion

8.84±0.88° and 0.46±0.05 Nm/°on extension

15.18±1.28° and 0.27±0.02 Nm/°on left bending

15.22±0.94° and 0.26±0.02 Nm/°on right bending

9.25±0.82° and 0.44±0.04 Nm/°on left rotation

and 9.21±0.73° and 0.44±0.04 Nm/°on right rotation. These  Results  revealed that the range of movement of the segments on flexion/extension

left/right bending and left/right rotation were significant increased in final trauma specimens compared to those of normal specimens (P0.01). There were also significant differences of stiffness in all movements between 2 groups (P0.01). There was no significant difference in bending and rotation between right and left (P0.05).  Conclusion  The fractural model established using vertebral pre-injury and incremental trauma approach in this study provides an ideal tool for biomechanical evaluation of the internal fixation devices of spine.