Buckling and Hydraulic Mechanisms in Orbital Blowout Fractures

Abstract

Since the first description of orbital blowout fractures, there has been much confusion as to their etiology. Two principal mechanisms have been proposed to explain their production, the buckling and the hydraulic mechanisms caused, respectively, by trauma to the orbital rim and the globe of the eye. The aim of this study was to evaluate both mechanisms qualitatively and quantitatively. Our protocol used intact cadavers, quantifiable intraocular pressure, variable and quantifiable force, and quantifiable bone strain distribution with strain gauge analysis. One orbit of each cadaver was used to simulate each of the two mechanisms, allowing direct comparison. Fractures produced by the buckling mechanism were limited to the anterior part of the orbital floor, with strain readings reaching up to 3756 microepsilon. Posteriorly, strain did not exceed 221 microepsilon. In contrast, hydraulic-type fractures were much larger, involving anterior and posterior parts of the floor as well as the medial wall of the orbit. Here, strain exceeded 3756 microepsilon in both parts of the floor. Furthermore, we have demonstrated that the average energy required to fracture the orbital floor by the buckling mechanism is 1.54 J, whereas an average energy of 1.22 J is needed to produce this fracture by the hydraulic mechanism. Our results suggest that efforts to establish one or another mechanism as the primary etiology are misplaced. Both mechanisms produce orbital blowout fractures, with different and specific characteristics. We believe this provides the basis for our reclassification of such fractures.

Role of Inferior Orbital Wall Morphologic Properties in Isolated Orbital Blow-Out Fracture

“…Increased intraorbital hydraulic pressure does not play a role in blow-in fractures. Recent cadaver studies demonstrated that the buckling mechanism causes small fractures without medial wall involvement, and the hydraulic mechanism causes larger fractures involving both the anterior and posterior parts of the inferior wall [5,14] . It seems that higher coefficient of curvature of the inferior wall in patients with inferior wall fracture is associated with the hydraulic theory of increased hydraulic pressure.…”

Orbital blowout fracture due to true hydraulic pressure

“…Fujino and Makino [2] described that in order to produce a blowout fracture by hydraulic pressure, a force greater than the forces applied would be necessary to cause the observed buckling of the orbital floor. In contrast, several recent experimental results have shown that the average energy necessary for fracture production by a hydraulic mechanism is close to that of a buckling mechanism [3,4]. In addition to these experiments, Lee [5] reported one case of a blowout fracture caused by a headlock, which supports the pure hydraulic theory.…”

“…They also described that if the primary causative factor was an increased hydraulic pressure, a high incidence of ocular injuries would be encountered. On the contrary, some detailed recent experimental results have shown that the average energy necessary for fracture production by a hydraulic mechanism is nearer to that required for the buckling mechanism [3,4,16]. Warwar et al [3] described that both mechanisms contribute to most clinically observed orbital floor fractures and the experimentally measured value required to fracture the orbital floor directly is significantly less than the previously reported energy value required to rupture a human eyeball.…”

Biomechanical analysis of likelihood of optic canal damage in peri-orbital fracture

“…As a study method for facial bone fracture, actual application of impacts on cadavers' orbits might be more convincing than dynamic calculation because reality is superior to simulation. Indeed, the mechanisms of orbital fracture used to be studied on cadavers in the past [13,14]. However, destruction of cadavers is ethically unacceptable nowadays.…”