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While the number of deaths from vehicle accidents is declining, probably because of mandatory seat belt laws and air bags, a high frequency of lower extremity injuries from frontal crashes still occurs. For the years 1979-1995 the National Accident Sampling System (NASS) indicates that knee injuries (AIS 1-4) occur in approximately 10% of cases. Patella and femur fractures are the most frequent knee injuries. Current literature suggests that knee fractures occur in seated cadavers for knee impact forces of 7.3 to 21.0 kN. Experimental data shown in a study by Melvin et al. (1975) further suggests that fracture tolerance of the knee may be reduced for an impact directed obliquely to the axis of the femur. The current study hypothesized that the patella is more vulnerable to fracture from an oblique versus an axial impact (directed along the femoral axis), and that the fracture pattern would vary with impact direction.

A comparative investigation of airbag and HANS driver safety systems was carried out (HANS, is a Registered Trademark in the U.S.A.). With both systems, head and neck loads were reduced from potentially fatal values to values well below the injury threshold. Both systems performed similarly in reducing the potential for driver injury. For this reason and given the high costs of development and testing, there is no justification for further development of airbags for racing.

Lower extremity injuries due to automobile accidents are often overlooked, but can have a profound societal cost. Knee injuries, for example, account for approximately 10% of the total injuries. Fracture of the knee is not only an acute issue but may also have chronic, or long term, consequences. The criterion currently used for evaluation of knee injuries in new automobiles, however, is based on experimental impact data from the 70''s using seated human cadavers. These studies involved various padded and rigid impact interfaces that slightly alter the duration of contact. Based on these data and a simple mathematical model of the femur, it appears fracture tolerance increases as contact duration shortens. In contrast, more recent studies have shown mitigation of gross fractures of the knee itself using padded interfaces. The use of padded interfaces, however, result in coincidental changes in contact duration and knee contact area.

The location of the pelvis in the seated automobile operator is critical for proper packaging and seat comfort design. The pelvis is the skeletal structure which contains the hip joint (H-point) and ischial tuberosity (D-point). The orientation of the pelvis largely determines the curvature in the low back which is supported by lumbar supports in the seat back. A methodology has been developed that uses onboard video and pressure measurement systems to locate the pelvis. This system has been used in a mid-sized vehicle on seated operators driving the vehicle on the highway. This paper describes the methodology and the location of the pelvis in seated automobile operators.

Lower extremity (knee) trauma is currently based on a bone fracture criterion derived from impacts of aged specimens. Recent clinical studies, however, indicate that a chronic disease (post-traumatic osteoarthritis), may be precipitated after mechanical insult without obvious bone fracture(1). It is hypothesized this is due to microcracking of subchondral bone under cartilage. This hard tissue layer is known to change with age and pathology. Ten ‘aged’ (71 years) and ten ‘young’ (47 years) cadaver knee joints were impacted to study the influence of age and pathology on the fracture load, and incidents of occult injury. Our results indicate that fracture load, per se, was independent of specimen age. On the other hand, severely pathological specimens required significantly higher loads to fracture bone. Occult microcraking was also observed in subfracture experiments, however, fewer incidents were recorded for the ‘aged’ specimens.