Comparison of Mechanical Stress on Implants in Anterior Single and Double Screw Fixation of Odontoid Fractures in a Finite Element Model.

Abstract

Aim: To evaluate the effect of single and double anterior odontoid screw fixation on the ROM of the craniocervical area and the stress distribution on the implants in a Finite Element Analysis which may give us ideas about the possible results for IF and malunion.

Material and methods: A FE model of the craniocervical area was constructed and a type II fracture model was created. In model A, a single screw and in model B two screws were used to fixate the model. The ROM and von Misses stress distribution on implants was evaluated.

Results: The ROM values of the models with fixation closely resembled those of the intact model, showing less than a 10% difference in ROM. Under loading conditions in flexion, extension, rotation and lateral bending directions for each model, both structures exhibited similar stress distributions. In both models, the stress was distributed throughout the whole shaft, whereas during lateral bending and rotation, the stress was localized more on the distal part. But the maximum stress on implants were higher in the single screw model.

Conclusion: We believe that double odontoid screws decrease the stress on implants, thus decreasing the risk of IF without significantly affecting ROM.