C Punke1, A Fritsche, H Martin, K P Schmitz, H W Pau, B Kramp. 1. Klinik und Poliklinik für Hals-Nasen-Ohrenheilkunde, Kopf- und Halschirurgie, Universität Rostock, Doberanerstr. 137-139, 18057 Rostock. Christoph.punke@med.uni-rostock.de
Abstract
BACKGROUND: Isolated orbital floor fractures make up a significant proportion of all facial injuries, but the mechanism involved in these injuries to the orbital walls (blow-out fractures) has not yet been completely defined. Two theories have been described, which seem to be mutually exclusive. According to the hydraulic pressure theory, the kinetic energy of the blow is transferred via the incompressible eye tissue to the floor of the orbita, which in turn fractures. The buckling force theory, in contrast, explains these fractures as the result of bending and shear stresses arising from kinetic energy act directly on the orbital rim. MATERIALS AND METHODS: With the aim of elucidating the mechanism of injury, we constructed a simplified finite-element model of the human orbita by 3D optical scanning of a human skull obtained after an autopsy examination. We created a generic approximation model based on empiric data derived from femoral fractures and reported in the literature. Several experiments were conducted to test both the above hypotheses by direct and indirect application of kinetic energy. RESULTS: We simulated different types of shear stress with the finite-element model of the skull. The calculated points of maximum pressure were all within the orbital floor. CONCLUSION: The simulation showed that both mechanisms can lead to fractures, as also documented by recent studies. The generation of a finite-element model and simulation of stresses were initially useful in establishing a method. More detailed studies on the empiric data relating to the various structures and more extensive determination and measurement of different skull and/or orbita geometries are needed before we can achieve a model in which the mechanical attributes of the structures involved are reproduced with closer approximation to the real-life situation.
BACKGROUND: Isolated orbital floor fractures make up a significant proportion of all facial injuries, but the mechanism involved in these injuries to the orbital walls (blow-out fractures) has not yet been completely defined. Two theories have been described, which seem to be mutually exclusive. According to the hydraulic pressure theory, the kinetic energy of the blow is transferred via the incompressible eye tissue to the floor of the orbita, which in turn fractures. The buckling force theory, in contrast, explains these fractures as the result of bending and shear stresses arising from kinetic energy act directly on the orbital rim. MATERIALS AND METHODS: With the aim of elucidating the mechanism of injury, we constructed a simplified finite-element model of the human orbita by 3D optical scanning of a human skull obtained after an autopsy examination. We created a generic approximation model based on empiric data derived from femoral fractures and reported in the literature. Several experiments were conducted to test both the above hypotheses by direct and indirect application of kinetic energy. RESULTS: We simulated different types of shear stress with the finite-element model of the skull. The calculated points of maximum pressure were all within the orbital floor. CONCLUSION: The simulation showed that both mechanisms can lead to fractures, as also documented by recent studies. The generation of a finite-element model and simulation of stresses were initially useful in establishing a method. More detailed studies on the empiric data relating to the various structures and more extensive determination and measurement of different skull and/or orbita geometries are needed before we can achieve a model in which the mechanical attributes of the structures involved are reproduced with closer approximation to the real-life situation.