[Three-dimensional finite element analysis of blowout fractures].

There are a number of theories as to how orbital fractures come about, but there are still a lot of unanswered questions regarding the dynamic characteristics of the orbit at the time of the fracture. To answer these questions, we analyzed the degree and concentration of stress within the orbit depending on the loads placed upon it. We used a computer to create a three-dimensional finite element model which could simulate the orbital fracture process. We found that direct force applied against the inferior orbital rim by forces outside the eye results in increased stress within the lower wall of the orbit, and that stress tends to concentrate in the thin nasal side of the orbital groove as pressure within the orbit mounts. When we compared these findings with clinical cases of orbital fracture, it became clear that the best way to explain the clinical data is by reference to the combined effect of direct force applied against the inferior orbital rim by elements outside the eye and the buildup of internal pressure within the orbit.