The effect of striking angle on the buckling mechanism in blowout fracture

BACKGROUND: The buckling mechanism is widely accepted as a mechanism of blowout fractures, along with the hydraulic mechanism. Although many studies have been performed related to the buckling mechanism, none of them have taken the direction of the striking force into consideration. As the orbital floor is not parallel to the horizontal plane, a difference in the striking force direction might affect resultant fracture patterns. The present study aims to investigate whether fracture patterns in the orbital floor were influenced by the striking force direction in terms of the buckling mechanism. METHODS: The authors produced three-dimensional models on a workstation simulating eight dry skulls and applied striking forces on the orbital rim of each model from three different angles (0, 15, and 30 degrees in the upward direction). Using finite element analysis, the authors calculated the width of the area where the resultant stresses exceed the bone's yielding criterion. The width was termed the "theoretical fracture width" because, theoretically, fracture was expected to occur in the area. Then, the authors compared the theoretical fracture width in groups with the three different striking force angles. Finally, the validity of the theoretical width was verified with an experiment on actual skull models. RESULTS: The theoretical fracture width was the greatest when the striking force was directed at 30 degrees in the upward direction. CONCLUSIONS: For the buckling mechanism, fracture would occur in a wider area of the orbital floor when striking force was directed upward than when the force was horizontally directed. This finding would be helpful in predicting fracture width in blowout fractures.