Studies were conducted on twenty-two fresh human cadavers to determine the probability of facial bone fracture following dynamic contact with steering wheel assemblies of both standard (a commercially available) and energy absorbing (EA) types. Using a specially designed and validated vertical-drop impact test system, either zygoma was impacted once onto the junction of the lower left spoke and rim with velocities ranging from 2.0 to 6.9 m/s. Generalized force histories were recorded with a six-axis load cell placed below the hub. The wheel was inclined 30 degrees to the horizontal. Steering wheel deformations were recorded with a system of potentiometers placed below the impact site on the wheel. Dynamic forces at the zygoma (impact site) were computed using transformation principles. A triaxial accelerometer was placed at the posterior parietal region of the specimen opposite to the impact site to record acceleration histories. High speed photography documented the kinematics. Tissues were evaluated using palpation, gross dissection, plain radiography, 2-D and 3-D CTs, and defleshing techniques. Fracture severity was graded on a scale of 1-4. Quasistatic responses of the cadaver zygoma and the steering wheels were also studied.
At impact velocities of 6.93 to 3.58 m/s for the EA wheel and 3.13 to 2.24 m/s for the standard wheel, severe fractures of the zygoma, zygomatic arch, maxilla and orbit were observed. These clinically significant fractures often require surgical intervention. A velocity of approximately 2.68 m/s for the EA wheel and 2.01 m/s for the standard wheel produced no clinically significant injury to the facial structure.