Numerous studies have documented that lower extremity injury is second only to the head and face in automotive accidents. Knee trauma typically results from high-speed contact with the instrument panel, which can produce fracture and subfracture level injuries. Current federal safety guidelines use a bone fracture criterion that is based solely on a peak load and 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 that 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; however, the cadaveric load-area data is not directly applicable to the dummy because of differences in geometry and material properties. A recent study developed a transformation protocol that provides a simple means of predicting the load-area response of the cadaver via load-area data recorded from a dummy experiment. In this study, 10 car crash simulations were conducted over a range of Delta-V's and a variety of restraint scenarios (unbelted, belted, full power airbag, and 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.

Lower extremity injuries during car accidents are common; the lower extremities are typically the first point of contact between the occupant and the car interior. Lower extremity injuries are not normally life threatening, but can represent a large societal burden through treatment costs, lost work days, and reduced quality of life. The purpose of this research was to study injuries of the knee and propose a methodology to prevent future knee injuries. Data from the National Accident Sampling System (NASS) showed that 10% of all injuries were to the knee, second only to head and neck injuries. Most knee injuries are a result of knee-to-instrument panel and subfracture injuries were most common, followed by gross fracture injuries. Cadaver data show that increasing the contact area for a given contact force over the knee greatly reduces acute injury in fracture and subfracture experiments. However, cadaver force-area data cannot be applied to the Hybrid III dummy, which is the most used human surrogate in car crash simulations. This study also sought to develop a transformation of the cadaver contact force-area relationship to the dummy. Numerous experiments were conducted on the dummy to establish a comparison with companion experiments conducted on cadavers. Data points representing a 50% risk of gross fracture were calculated for the cadaver and transformed into the dummy response to yield data directly relevant to sled testing with dummies. Several sled tests were run using an idealized instrument panel to show the utility of the data in predicting joint injury for depowered air bags and various restraint scenarios. Mathematical models were used to show a theoretical scenario in which load and area could be estimated without the need for sled testing. This study shows that a simple measure of knee contact load and area could be used to predict injuries in the cadaver knee from blunt insult via dummy test data and hopefully provide increased knee injury protection for car occupants.