Mechanisms of Orbital Floor Fractures

Abstract

The purpose of this study was to investigate the two accepted mechanisms of the orbital blowout fracture (the hydraulic and the buckling theories) from a clinical, experimental, and theoretical standpoint. Clinical cases in which blowout fractures resulted from both a pure hydraulic mechanism and a pure buckling mechanism are presented. Twenty-one 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 the fracture of thin-walled truncated conical shells were used to predict the energy required to fracture the bone of the orbital floor via the hydraulic and buckling mechanisms. Experimentally, the mean energy required to fracture the bone of the human cadaver orbital floor directly was 78 millijoules (mJ) (range, 29-127 mJ). Using the engineering formula for the hydraulic theory, the predicted theoretical energy is 71 mJ (range, 38-120 mJ); for the buckling theory, the predicted theoretical energy is 68 mJ (range, 40-106 mJ). Through this study, we have experimentally determined the amount of energy required to fracture the bone of the human orbital floor directly and have provided support for each mechanism of the orbital blowout fracture from a clinical and theoretical basis.