Biomechanical Comparison of Odontoid Plate Fixation Versus Odontoid Screw Fixation

Abstract

Randomized controlled trial with statistically significant difference or statistically no significant difference (Level I). The purpose of this study was to measure the mechanical stability of odontoid plate fixation, using a specially designed plate construct and to compare the results with those after odontoid single-screw and double-screw fixation. Plate fixation of the odontoid process without C1-C2 is a possible option for the management of odontoid fractures that are not suitable for conventional screw fixation. Although earlier biomechanical works have evaluated the effectiveness of different odontoid screw fixation techniques, no study has quantified the mechanical stability of odontoid fixation by a plate device. The second cervical vertebra was removed from 15 fresh human spinal columns. The specimens were fixed to the experimental apparatus with the load cell at the articular surface of the odontoid process. In the first test series, stiffness and failure load of the intact odontoid were measured. Type II odontoid fractures were created by a 45 degree oblique extension loading at the articular surface of the odontoid process. Afterward, the specimens were randomly assigned to 1 of the following 3 groups: in group I (n=5), the fractures were stabilized, using a specially designed plate construct, in group II, the fractures were fixed, using two 3.5 mm cortical screws, and in group III, we used 1 regular 4.5 mm cortical screw. In the second test series, stiffness and failure load of the stabilized odontoid fractures were assessed for comparison and statistical analysis. Group I (plate device) showed a significantly higher mean failure load than group II and group III. The mean failure load of group I, after fixation of the odontoid fracture, was 84% of the mean failure load that was necessary to create a type II odontoid fracture initially. Comparing group II (double screw technique) and group III (single screw technique), there was no significant difference regarding the mean failure load. In both groups, the mean failure load after odontoid fixation was approximately 50% of the mean failure load of the intact odontoid. Statistical analysis also revealed a significantly higher stiffness of the stabilized odontoid after plate fixation than after single- or double-screw fixation. Plate fixation of the odontoid process for certain type II odontoid fracture patterns provided a significantly higher biomechanical stability than the technique of odontoid screw fixation. Using a specially designed plate construct fixed with 2 cancellous screws into the body of C2 and an additional cortical screw inserted in the odontoid process, 84% of the original stability of the intact odontoid was restored. Single- or double-screw fixation of the odontoid only restored approximately 50% of the original strength.