Biomechanical and anatomic study of the fragment in spinal canal for the thoracolumbar burst fracture .

Objective: To study the anatomic factors of the reduction of fragment in the spinal canal for thoracolumbar burst fracture and the related biomechanic relationship. Methods: Using burst fracture model of L 1 made by fresh thoracolumbar spine (T 11～L 3), the change of the narrowest place in the spinal canal under axial distraction was drew. At the same speed for group one with the posterior longitudinal ligament (p11)being intact and the fibrous annulus being cut off, group two with the fibrous annulus being intact and the pll being cut off, group three with both being intact, the curve of the relationship between the reduction percentage of fragment and the axial distraction was drawn. Results: Curves of the relationship between the reduction percentages of fragment and the axial distraction were "s" shaped . Curves ascended slowly and the axial distractions rised progressively on the sequence of Group Ⅰ,Ⅱ, Ⅲ in pre-reduction period .Curves ascended acutely in reduction period. The axial distraction and the reduction percentages rised on the sequence of Group Ⅰ, Ⅲ and Ⅱ.There was still a significant reduction curve during the post-reduction period. Conclusion: The axial distraction takes an important role on the reduction of fragment in the spinal canal for the thoracolumbar burst fracture, and intact pll and fibrous annulus take a key role in the course of the reduction of fragment.