Development of Injury Criteria for Human Surrogates to Address Current Trends in Knee-to-Instrument Panel Injuries

Injuries to the lower extremities are common during car accidents because the lower extremity is typically the first point of contact between the occupant and the car interior. While injuries to the knee, ankle and hip are usually not life threatening, they can represent a large societal burden through treatment costs, lost work days and a reduced quality of life. The aim of the current study was to specifically study injuries associated with the knee and to propose a methodology which could be used to prevent future knee injuries. To understand the scope of this problem, a study was designed to identify injury trends in car crashes for the years 1979-1995. The NASS (National Accident Sampling System) showed that 10% of all injuries were to the knee, second only to head and neck injuries. Most knee injuries resulted from knee-to-instrument panel contact. Subfracture injuries were most common (contusions, abrasions, lacerations) followed by gross fracture injuries. Our recent studies on the human cadaver knee show that increasing the contact area for a given contact force over the knee significantly reduces acute injury in fracture and subfracture experiments. Unfortunately, the cadaver force-area data cannot be directly applied to the Hybrid III dummy, which currently serves as a human surrogate in car crash simulations. Thus, another aim of this study was 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 a variety of restraint scenarios. Mathematical models were developed to demonstrate a theoretical scenario in which load and area could be estimated without the need for physical sled testing. This study shows that a simple measure of the knee contact load and area could be used to predict injuries in the human cadaver knee from blunt insult via dummy test data. Such data may prove useful in the design of future instrument panels to provide increased knee injury protection for car occupants.