Mechanisms of orbital floor fractures - A clinical, experimental, and theoretical study

Purpose: The purpose of this study was to investigate the two accepted mech anisms of the orbital blowout fracture (the hydraulic and the buckling theo ries) from a clinical, experimental, and theoretical standpoint. Methods: Clinical cases in which blowout fractures resulted from both a pur e hydraulic mechanism and a pure buckling mechanism are presented. Twenty-o ne intact orbital floors were obtained from human cadavers. A metal rod was dropped, experimentally, onto each specimen until a fracture was produced, and the energy required in each instance was calculated. A biomathematical model of the human bony orbit, depicted as a thin-walled truncated conical shell, was devised. Two previously published (by the National Aeronautics and Space Administration) theoretical structural engineering formulas for t he fracture of thin-walled truncated conical shells were used to predict th e energy required to fracture the bone of the orbital floor via the hydraul ic and buckling mechanisms. Results: Experimentally, the mean energy required to fracture the bone of t he human cadaver orbital floor directly was 78 millijoules (mJ) (range, 29- 127 mJ). Using the engineering formula for the hydraulic theory, the predic ted theoretical energy is 71 mi (range, 38-120 mi), for the buckling theory , the predicted theoretical energy is 68 mi (range, 40-106 mi). Conclusion: Through this study, we have experimentally determined the amoun t of energy required to fracture the bone of the human orbital floor direct ly and have provided support for each mechanism of the orbital blowout frac ture from a clinical and theoretical basis.