Evaluation of biomechanical changes on upper endplate with C4 transcorporeal tunnel using a C2~T1 finite element model

Abstract:

Objective：To evaluate the biomechanical changes on C4 superior endplate with different types and diameters of transcorpo－real tunnels. Methods：A C2~T1 finite element model was built with CT data of neck from a healthy male volunteer. After validation of the FE model，two groups（A and B） of C2~T1 models was built with C4 tunneled with or without endplate excision and diameters of 6 mm，8 mm and 10 mm（1/2，2/3 and 6/5 of anterior C4 vertebral body height）. 1 N/m of flexible moment was loaded to FE models and the biomechanical changes on C4 superior endplate was evaluated. Results：There were stress concentration on the margin of ex－cision on C4 superior endplates in group A；in group B only B10 showed stress concentration on C4 superior endplate. All the areas and values of stress concentration increased with diameter in two groups. Maximum stress on C4 superior endplates in two groups was A6：11.51 MPa，A8：17.33 MPa，A10：18.49 MPa and B6：2.57 MPa，B8：2.89 MPa，B10：3.65 MPa. One-way analysis of variance of the stress distribution of C4 on superior endplate between tunneled model and intact model showed that B6 and anterior of B8 end－plates had no significant difference with the intact model（P>0.05），while in other models the differences were significant（P=0.000）. Evaluation of the risk of fracture on endplates showed that there were different amounts of high risk elements（A6：0.8%；A8：2.3%；A10：7.2%） in group A while few risk elements in group B. Conclusion：Those tunnels on vertebrae with endplate excision would cause stress concentration and risks of end－plate fracture. Maintaining the integrity of superior endplate can avoid those risks. In order to avoid risks of endplate fracture，diameter of tunnels on vertebrae without endplate excision should be limited within 2/3 of anterior vertebral body height，diameter of tunnels on vertebrae with endplate excision should be limited within 1/2 of anterior vertebral body height.