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Lower extremity injuries are a frequent outcome of automotive accidents. While the lower extremity injury criterion is based on fracture of bone, most injuries are of less severity. Recent studies suggest microscopic, occult fractures that have been shown to be precursors of gross bone fractures, may occur in the kneecap (patella) for impacts with rigid and deformable interfaces due to excessive levels of patello-femoral contact pressure. One method of reducing this contact pressure for a 90° flexed knee is to provide a parallel pathway for knee impact loads into the tibial tuberosity. Yet, blunt loads onto the tibial tuberosity can cause posterior drawer motion of the tibia, leading to injury or rupture of the posterior cruciate ligament (PCL). Recently studies have shown that axial loads in the tibia, which are measured during blunt loading on the knee in typical automobile crashes, can induce anterior drawer motion of the tibia and possibly help unload the PCL.

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.

According to the National Accident Sampling System (NASS), 10% of all automobile accident injuries involve the knee. These injuries involve bone fracture and/or “soft tissue” injury. Previous investigators have determined the tibial-femoral (TF) joint failure load for an experimentally constrained human knee at 90° flexion. In these experiments bone fractures have been documented. During TF joint compression, however, anterior motion of the tibia has been noted by others. It was therefore the objectives of this study to document effects of flexion angle and anterior-posterior joint constraint on the nature and severity of knee injury during TF compression loading via axial loads in the tibia. The effect of flexion angle was examined using 10 unconstrained human knees from 5 cadavers aged 73.2±9.4 years.

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.

Lower extremity (knee) injury prediction resulting from impact trauma is currently based on a bone fracture criterion derived from experiments on predominantly aged cadavers. Subsequent experimental and theoretical studies indicate that more aged, pathological specimens require higher, not lower, loads to initiate bone fracture. This suggests that a bone fracture criterion based solely on aged specimens may not be representative of the current driving population. In the current study, we sought to determine if cadaver age, physical size, sex, baseline joint pathology, or patellar geometry correlated with fracture load. An analysis was made of data from previous impact experiments conducted on fifteen isolated cadaver knees using a consistent impact protocol. The protocol consisted of sequentially increasing the impact energy with a rigid interface until gross fracture. Gross bone fractures occurred at loads of 6.9±2.0 kN (range 3.2 to 10.6 kN) using this protocol.

Injury to the lower extremity during an automotive crash is a significant problem. While the introduction of safety features (i.e. seat belts, air bags) has significantly reduced fatalities, lower extremity injury now occurs more frequently, probably for a variety of reasons. Lower extremity trauma is currently based on a bone fracture criterion derived from human cadaver impact experiments. These impact experiments, conducted in the 1960's and 70's, typically used a rigid impact interface to deliver a blunt insult to the 90° flexed knee. The resulting criterion states that 10 kN is the maximum load allowed at the knee during an automotive crash when certifying new automobiles using anthropomorphic dummies. However, clinical studies suggest that subfracture loading can cause osteochondral microdamage which can progress to a chronic and debilitating joint disease.

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.

Head-to-knee interaction of the right front passenger dummy can occur in some 30-35 MPH crash barrier tests. The biofidelity and significance of these interactions as related to predicting human response was addressed in this study. In a series of laboratory experiments an instrumented headform was dropped on the dummy knee to simulate the barrier interactions. These test results were then related to the human by dropping the same headform on the cadaver leg. The instrumented headform was dropped from three heights to impact the Part 572 dummy knee at three velocities. Two impact sites and two impact angles were used. These test parameters bracketed the barrier conditions. Measurements from headform accelerometers permitted calculation of HIC value for comparison to barrier values. Comparable experiments were subsequently performed with three unembalmed cadaver subjects using the same headform and test procedures.

Knee bolsters on the lower instrument panel have been designed to control occupant kinematics during sudden deceleration. However, a wide variability in car occupant anthropometry and choice of seating posture indicates that lower-extremity contacts with the impingement bolster could predominantly load the flexed leg through the knee (acting through the femur) or through the tibia (acting through the knee joint). Potential injuries associated with these types of primary loading may vary significantly and an understanding of potential trauma mechanisms is important for proper occupant restraint.

This study explores the application of viscoelastic modeling for characterization of the response of the brain to impulsive loading with the objective of learning whether such models could exhibit the same time dependency of strain or likelihood of injury, as exhibited by the Severity Index, HIC Index, Wayne Tolerance Curve, and other similar representations of tolerance. The mathematical relationships between viscoelastic properties and the corresponding time dependency of tolerance are shown for Newtonian, Bingham plastic, and Pseudo-Bingham, as well as more general behavior. Preliminary static and dynamic tests upon small mammalian material are described with particular attention given to strain in the vicinity of the brainstem as a function of loading profile. Both the theoretical and experimental results show that the falling time dependency of the above indexes can be interpreted in terms of nonlinear viscoelastic response.