Biomechanic Factors Associated With Orbital Floor Fractures

Abstract

lowout fractures of the orbit, a term first put forth by Smith and Regan, 1 describes a specific set of fractures of the orbital bone often resulting from blunt trauma. Most commonly this refers to fractures of the orbital floor but can also include the medial orbital wall or the roof of the orbit. To further explain the mechanism underlying this type of fracture, the "buckling" theory and the "hydraulic" theory have been previously proposed. 2,3 The buckling theory contends that injury-but not fracture-to the infraorbital rim then leads to a fracture of the more delicate orbital floor. The hydraulic theory purports that insult to the globe itself transmits pressure to the orbital floor, thereby inducing a fracture. 4 However, in attempting to evaluate these theories, many previous studies have had inconsistences in their study design. For example, several studies 5,6 used fixed cadaveric skulls and failed to properly quantify the forces applied. Recent work by Ahmad et al 7 analyzed direct trauma to both the globe and rim in the orbits of fresh, intact, human postmortem cadavers using strain gauges in an attempt to test both the hydraulic and buckling mechanisms. Their experimental setup allowed for both qualitative and quantitative assessment of orbital floor fracture and demonstrated that the buckling mechanism tends to produce fractures in the anterior and anteromedial aspects of the orbital floor, whereas the hydraulic mechanism tends to produce fractures in the posterior aspects of the orbital floor. Our hypothesis is that both the hydraulic and buckling theories will manifest similar force thresholds required for fracture; however, anatomical fracture patterns will differ and can provide clinical data on the necessity of ophthalmologic evaluation. Methods The study was exempt from institutional review board approval because there were no HIPAA issues or human studies and only cadavers were used. A total of 10 orbits from 5 heads (3 male and 2 female) were used for this study. These came from IMPORTANCE Orbital floor fractures are commonly seen in clinical practice, yet the etiology underlying the mechanism of fracture is not well understood. Current research focuses on the buckling theory and hydraulic theory, which implicate trauma to the orbital rim and the globe, respectively. OBJECTIVE To elucidate and define the biomechanical factors involved in an orbital floor fracture. DESIGN, SETTING, AND PARTICIPANTS A total of 10 orbits from 5 heads (3 male and 2 female) were used for this study. These came from fresh, unfixed human postmortem cadavers that were each selected so that the cause of death did not interfere with the integrity of orbital walls. Using a drop tower with an accelerometer, we measured impact force on the globe and rim of cadaver heads affixed with strain gauges. RESULTS The mean impacts for rim and globe trauma were 3.9 J (95% CI, 3.4-4.3 J) and 3.9 J (95% CI, 3.5-4.3 J), respectively. Despite similar impact forces to the globe and rim, strain-gauge data displayed greater mean strain for...

Validation of Hydraulic Mechanism during Blowout Trauma of Human Orbit Depending on the Method of Load Application

“…Interestingly, the energies of the impact during the hydraulic mechanism causing the orbital wall damage reported by almost all other authors are unquestionably lower than those observed in the current work. Exempli gratia, according to simulations of Nagasao et al, the impact energy of 0.933 J is believed to initiate the fracture within the orbit for hydraulic mechanism [ 11 ], while the computations of Patel et al showed that the impact energies causing both lower and medial wall fractures were from the range of 3.0–5.0 J [ 6 ]. On the contrary to the above values, the calculated total strain energy corresponding to the very first moment of exceeding the applied H-M-H limit in the current model (MOBOSE) was 16.4 J.…”

“…Worth noting, the novel element of the current investigation is the successful attempt to model the blowout type of trauma as the orbit was loaded indirectly via the contact interactions of the intraorbital soft tissues subjected to the set of forces directly, unlike what other authors did such as Al-Sukhun et al [ 7 , 13 , 30 ], Schaller et al [ 12 ], Patel et al [ 6 ], and Foletti et al [ 8 , 9 ]. Those models concern the blunt type of impact when a rigid/deformable body collided with a deformable model of a human skull.…”

“…As long as any controversy has not aroused around the essence of the buckling mechanism during previous studies [3][4][5][6], still, some descriptions of a sufficiently precise model of the hydraulic mechanism involving the set of intraorbital entities into cooperation (MOBOSE) are available in the literature. Until the works of Al-Sukhun et al [7], as well as Patel et al [6], and Foletti et al [8,9], other attempts were taken to model the hydraulic mechanism, but the role of the intraorbital tissues was omitted there. Nagasao et al built their models basing on the hydraulic pressure applied to the internal faces of the orbital walls [10,11].…”

“…Al-Sukhun et al were the first who presented the model of a blowout injury involving the intraorbital tissues into consideration during the hydraulic mechanism simulation; nevertheless, their FEM model was not built basing on the real skull geometry (CT scans) [ 13 ]. On the contrary to them, in the latest work of Patel et al [ 6 ], the human head model with the detailed ocular anatomy was used to determine the energy thresholds of the impact required to procure the orbital wall fracture both for the buckling and hydraulic mechanisms. However, the model was described rather superficially, without details necessary to repeat those calculations.…”

The better surgical timing and approach for orbital fracture: a systematic review and meta-analysis

“…There are many factors affecting the results of surgery, including the timing of surgery, repair materials, and surgical approach (6)(7)(8)(9). Most orbital fractures do not require immediate repair, depending on the severity and type of fracture.…”