Application of a Knee Injury Criteria for the Hybrid III Dummy to Address a Variety of Car Crash and Restraint Scenarios

Numerous studies have documented that lower extremity injury is second only to the head and face in automotive accidents. Such injuries are common because the lower extremity is typically the first point of contact between the occupant and the car interior. Of all lower extremity injuries, the knee is the most common site of trauma. This typically results from high speed contact with the instrument panel which can produce fracture and subfracture (contusions, lacerations, abrasions) level injuries. Current Federal safety guidelines use a bone fracture criterion which is based solely on a peak load. The criterion states that loads exceeding 10 kN will likely result in gross bone fracture. However, cadaver experiments have shown that increased contact area (via padding) over the knee can significantly increase the amount of load that can be tolerated before fracture or subfracture injury. Thus, injury prediction protocols which account for both load and contact area over the knee would produce a more sensitive injury criterion. Currently, knee injury is assessed in car crash simulations using Hybrid III dummies. Unfortunately, the cadaveric load-area data is not directly applicable to the dummy due to differences in geometry and material properties. A recent study developed a transformation protocol which provides a simple means of predicting the load-area response of the cadaver via load-area data recorded from a dummy experiment. In the current study 10 car crash simulations were conducted using a generic sled and two different, idealized knee bolster materials. Tests were conducted over a range of Delta-V's and a variety of restraint scenarios (unbelted, belted, full power airbag, depowered airbag). After transformation of the dummy load-area data, it was concluded that the injury risk in a corresponding cadaver test was heavily dependent on the composition of the knee bolster and the kinematics of the dummy. More specifically, stiffer knee bolsters, insufficient restraint, and large delta-V's contributed to an increased risk of knee fracture. Such data are useful in the design of future instrument panels and car interiors to provide increased knee injury protection for car occupants.