The Design And Biomechanical Evaluation Of A New Type Of Anterior Cervical Plate Fixation System

Objiective: In order to enhance the fixation strength of anterior cervical plate and reduce the occurrence of screw pullout or breakage, a new type of anterior cervical plate system was designed based on the anatomic character of Chinese people to evaluate the biomechanical capability in cervical spine and provide scientific evidence for its preliminary clinical application.Methods: This study was divided into two parts. Part one: The design of the new type of anterior cervical plate fixation system. In order to obtain the anatomic parameters of anterior cervical spine of Chinese people to design the plate fixation system, the related literatures were reviewed, and the height, width and depth of human healthful cervical vertebral body were measured on X-ray pictures of clinical patients and during the operations. Part two is for biomechanical study of the new type anterior cervical fixation system. To evaluate the biomechanical capability of cervical spine, 12 fresh cervical spine specimens (C₂～T₁) from young male cadavers were used which had been made into flexion injury models and were randomly divided into 4 groups. Group A: the home-made plate was fixed by 6 screws, both of the upper and lower fixed vertebrae was fixed by 3 screws. Group B: the home-made plate was fixed by 4 screws, both of the upper and lower fixed vertebrae was fixed by 2 screws. Group C: each of the specimens was fixed by anterior Kanchui plate and posterior Cervifix rod-screws. Group D: each of the specimens was fixed by anterior Kanchui plate. The displacement, strength, stiffness of the spinal models were tested under flexion, extension, left and right bending, torsion respectively. The results were statistically analyzed. And furthermore, two sets of the plates were subjected to pull-out test and fatigue test, pull-out strength and fatigue strength were recorded and observed.Results: The biomechanical study shows the difference of displacement, strength and stiffness measurements between group A and B under various models such as flexion, extension, lateral bending and torsion was significant (P<0.05); the difference between group A and group D was significant, too (P<0.05); and the measurements of group C were more than that of group A, the difference was significant (P<0.05). The maximum pull-out strength of 6 screws fixed group was more than 4 screws fixed group, and its fatigue strength was 473.27Mpa. The systems could bear 5.5×10⁵ times of loading on average before they appeared fissures external to screw holes, which was sufficient for the safety of long-term fixation.Conclusion: The new type anterior cervical plate fixation system can provide more biomechanical stability, anti-pullout strength and anti-fatigue strength to cervical spine, and it is suitable to Chinese cervical vertebrae in anatomical size.