Biomechanical properties of a novel automatic anti-rotation posterior atlantoaxial internal fixation system: a finite element analysis / 中国组织工程研究

ABSTRACT

BACKGROUND: Atlantoaxial posterior approach is currently the main surgical treatment for atlantoaxial instability and/or dislocation, but the shape of rod in normal screw-rod device system is cylindrical. To obtain satisfactory reduction of atlantoaxis, the rod will be pre-bent obviously before fixation; however, the cylindrical rod will be rotated when tighten the nuts. Extra devices will be required to adjust and maintain the direction of the rod, thereafter, the surgical field will be blocked by the device, and spinal injury will occur once the devices are not held tightly. While the novel automatic anti-rotation rod has the function of anti-rotation during nut-tightening process, and also holds all the advantages of normal rod. Further research should be performed for the differences in biomechanical characteristics between two methods.OBJECTIVE: To investigate the biomechanical properties of the novel automatic anti-rotation rod for internal fixation system of atlantoaxial posterior approach based on three-dimensional finite-analysis model of upper cervical spine.METHODS: The three-dimensional finite element model of upper cervical spine with internal rod fixation system was developed. The biomechanical characteristics of the internal fixation system were analyzed. RESULTS AND CONCLUSION: The traditional and novel three-dimensional finite element model with realistic and geometric similarity contained 198330 elements, 964747 nodes and 246788 elements, 996069 nodes,correspondingly. There was no obvious stress concentration in both two systems, stress was concentrated mainly in the screw-bone and screw-rod interfaces. The stress values of the novel system were higher than those of the traditional system, but the maximum Von Misses Stress of two systems was lower than the yield (795-827 MPa ) and ultimate (860-896 MPa) strength of titanium alloys. These results show that the design of the novel automatic anti-rotation rod-screw fixation system has matched the biomechanical requirements for new internal fixation instruments, and is one safe, effective and practical device for atlantoaxial posterior procedure showing promising application prospect.