Biomechanic Factors Associated With Orbital Floor Fractures

Abstract

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 globe impact (6563 μS) compared with rim impact (3530 μS); however, these data were not statistically significant (95% CI, 3598-8953 μS; P = .94).

Conclusions and relevance: Our results suggest that trauma directly to the globe predisposes a patient to a more posterior fracture while trauma to the rim demonstrates an anterior predilection. Both the hydraulic and buckling mechanisms of fracture exist and demonstrate similar fracture thresholds.

Level of evidence: NA.

Figure 1.. Fracture Thickness Map

Fracture map showing regions from where bone thickness measurements were taken (A-G) and approximate position of strain gauge (dashed boxes). The central solid double line demonstrates the approximate location of infraorbital nerve as it courses through the orbital floor.

Figure 2.. Fracture Map

A, Rim; 3.86 J; maximum strain 5419 microstrains (μS); minimum strain, −6906 μS; maximum shear, 5395 Pa. B, Globe, 3.88 J; maximum strain, 6275 μS; minimum strain, −6043 μS; maximum shear, 6085 Pa.

Figure 3.. Orbital Floor Thickness Map

Values of defined regions listed in millimeters. The approximate position of strain gauge (dashed box) is displayed. The central solid double line demonstrates the approximate location of infraorbital nerve as it courses through the orbital floor.

Figure 4.. Correlation of Strain and Injury Severity

Each data point represents an orbital floor fracture. μS indicates microstrains.

Figure 5.. Correlation of Floor Thickness and Injury Severity

Each data point represents an orbital floor fracture.