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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.

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.

This work describes the development of a three-dimensional finite element model of the human arm. Mechanical properties of the arm were determined experimentally for use in the model development. The arm model is capable of predicting kinematics and potential injury when interacting with a deploying airbag. The arm model can be easily integrated with available finite element and rigid body dummy models. This model includes the primary components of a human arm. It includes all the bones of hand, ulna, radius and humerus. Anthropometry, moment of inertia, joint torque and tissue compressive properties were determined experimentally from human cadaveric subjects. To calibrate the model, both free-swinging motion and pendulum impact tests were used. The global responses of the pendulum force, pendulum velocity and the angle of rotation time histories of the arm were obtained and compared reasonably well with the experimental data.

Previous experimental and theoretical studies on isolated human knees have shown that increasing the contact area over the knee during blunt impact can prevent serious knee injury (i.e. joint fracture). Because large contact areas are typically associated with lower stiffness impact interfaces, this suggests that instrument panels could provide some protection to the knee during a car accident. Further, the knee-to-IP contact is one of the first contact events which occur during a head-on crash, thus, one optimal scenario might be to dissipate as much energy as possible at the knee without causing serious knee injury. This would help minimize the kinetic energy in the upper body, possibly reducing the need for more aggressive countermeasures (i.e. air bags) later in the impact event. Our objective in the current study was to determine how different car interior geometries and crash pulses would affect specific occupant responses during a head-on car crash.