Objective When fractured, zygomas rotate and dislocate. The present study quantitatively elucidates the pattern of the rotation. Methods 50 patients with tri-pod-type zygoma fractures were involved in this study. After defining a 3-dimensional coordinate system - consisting of the M-L axis (the axis directed from the medial to lateral side of the skull), I-S axis (directed from the inferior to superior side), and P-A axis (directed from the posterior to anterior side), the degree with which the fractured zygomas rotated around each of these axes was measured using 3-dimensional graphic software. Thereafter, the tendency of the rotation was compared between the three rotational axes. Results Rotation around the I-S axis was the most frequent with a 96% incidence, followed by a substantial margin by rotation around the M-L axis with a 26% incidence; rotation around the P-A axis was rare, with an incidence of 10%. Furthermore, the degree of P-A axis rotation was minor compared to I-S and M-L axis rotations. Conclusion The main factor of zygoma dislocation in zygoma fracture is rotation around the I-S axis. This finding is helpful for effective performance to reposition fractured zygomas.
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