In seatbelt wearing population, the steering wheel assembly is often implicated as a causal agent responsible for facial trauma. This study was conducted to determine the probability of facial fracture secondary to steering wheel impacts. The biomechanical and pathological injury characteristics were evaluated.
Fifteen fresh isolated human cadaver heads were impacted once in the region of either zygoma onto the junction of the left lower spoke and rim of a standard (SD) or an energy absorbing (EA) steering wheel. A custom designed and validated vertical-drop impact test system was used to conduct the controlled impact studies. Generalized force and deformation histories were recorded using a six-axis load cell placed at the hub and a system of potentiometers placed below the impact site on the steering wheel, respectively. A tri-axial accelerometer placed on the specimen measured the accelerations. The specimens were x-rayed in AP, lateral and Waters views, and abutting 1.5 mm two-dimensional (2-D) computerized tomography (CT) sections were taken before the test. Following impact, the tissues were studied underpalpation, gross dissection, radiography, and 2-D CT. Finally, the specimens were defleshed. Using a state-of-the art workstation available in our institution, three-dimensional reconstructions of the pre-test and post-test 2-D CT images were obtained. Fractures correlated well with peak forces, but poorly with HIC, accelerations, deformations contact areas, and mineral content of the bone. Zygomatic arch, tripod, orbit, maxilla, and other typical facial fractures of the middle and lower face were identified in the 3-D CT images. A good correlation was obtained between the defleshed preparations and 3-D CT images. While it was difficult to detect hairline and some mild non-displaced fractures with this method, clinically significant fractures were routinely identified. This technique, therefore, holds substantial promise for clinical evaluation of facial fractures which require surgical reconstruction.
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