Design And Related Study For Expanded Lumbar Interbody Fusion Cage

Objective To design a new type cage with enough initial stability, without pedicle screw fixation and evaluate the biomechanics stability. Methods The parameters related to new type cage design were obtained from anatomic measurements of lumbar specimen and human MRI scans. At the basis of the parameters, the new expended cage was designed. The biomechanics in vitro and finite element model were used to investigate the difference of biomechanical stability and self-stability three cages including: expended cage, threaded cage (Interfix) and impacted cage (Telamon). The goat latero-posterior lumbar intervertebral fusion model was established and compared with the results of groups interbody fusion with different excision rang of zygapophysial joints. Result The new type cage was designed nearly cuboid before expand during implantation procedure, then expanded , by impulsing the bolt in the posterior part of the cage, to increase the cage (intervertebral height and the contact area); teeth(height 1.5mm) on the contact surface. The expended angle was 8°, and the pattern had four kinds( 7,8,9,10mm) . Expended cage significantly decreased the ROM in flexion , extention ,lateral bending and rotation compared with Interfix and Telamon. The median pullout force of expended cage was 98.1% and 32.4% more than those of Telamon and Interfix respectively. The most dislodgement of cages were in rotation and the least were in flexion and extention. The median dislodgement of expended was least(0.085mm, 0.05mm in left rotation～0.11mm in flexion), compared to the other two type cages. The animal test showed zygapophysial joint play an important role in interbody fusion. Conclusion Theoretically the new type expended cage could be used alone without posterior pedicle screw fixation because of itself good biomechanical stability and self-stability.