Rodney W. Rudd

THE EFFECT OF TIBIAL CURVATURE AND FIBULAR LOADING ON THE TIBIA INDEX

The tibia index (TI) is commonly used to predict leg injury based on measurements taken by an anthropomorphic test device (ATD). The TI consists of an interaction formula that combines axial loading and bending plus a supplemental compressive force criterion. Current ATD lower limbs lack geometric biofidelity with regard to tibial curvature and fibular load-sharing. Due to differences in tibial curvature, the midshaft moments induced by axial loading are different in humans and ATDs. Midshaft tibial loading in the human is also reduced by load-sharing through the fibula, which is not replicated in current ATDs. In this study, tibial curvature and fibular load-sharing are quantified through CT imaging and biomechanical testing, and equations are presented to correct ATD measurements to reflect the loading that would be experienced by a human tibia.

SMALL FEMALE HEAD AND NECK INTERACTION WITH A DEPLOYING SIDE AIRBAG

OBJECTIVE This paper presents dummy and cadaver experiments designed to investigate the injury potential of an out-of-position small female head and neck from a deploying side airbag. METHODS Seat-mounted, thoracic-type, side airbags were selected for this study to represent those currently available on selected luxury automobiles. A computer simulation program was used to identify the worst case loading position for the small female head and neck. Once the initial position was identified, experiments were performed with the Hybrid III 5th percentile dummy and three small female cadavers, using three different inflators. RESULTS Peak head center of gravity (CG) accelerations for the dummy ranged from 71x g to 154 x g, and were greater than cadaver values, which ranged from 68 x g to 103 x g. Peak neck tension as measured at the upper load cell of the dummy increased with inflator aggressivity from 992 to 1670N. A conservative modification of the US National Highway Traffic Safety Administrations (NHTSAs) N(ij) proposed neck injury criteria, which combines neck tension and bending, was used. All values were well below the 1.0 injury threshold for the dummy and suggested a very low possibility of neck injury. In agreement with this prediction, no injuries were observed. CONCLUSIONS Even in a worst case position, small females are at low risk of head or neck injuries under loading from these thoracic-type airbags; however, injury risk increases with increasing inflator aggressivity.

Development of injury criteria for pelvic fracture in frontal crashes

Objective. This article assesses the position-dependent injury tolerance of the hip in the frontal direction based on testing of eight postmortem human subjects. Methods. For each subject, the left and right hemipelvis complex was axially loaded using a previously developed test configuration. Six positions were defined from a seated femur neutral condition, combining flexed, neutral, and extended femur positions with abducted, neutral, and adducted positions. Results. Axial injury tolerances based on peak force were found to be 6,850 ± 840 N in the extended, neutral position and 4,080 ± 830 N in the flexed, neutral position. From the flexed neutral orientation, the peak axial force increased 18% for 20° abduction and decreased 6% for 20° adduction. From the extended, neutral orientation, the peak axial force decreased 4% for 20° abduction and decreased 3% for 20° adduction. However, as there is evidence that increases in loading may occur after the initiation of fracture, the magnitude of the peak force is likely related to the extent of injury, not to the initial tolerance. Using the axial femur force at the initiation of fracture (assessed with acoustic crack sensors) as a potentially more relevant indicator of injury may lower the existing injury criteria. This fracture initiation force varied by position from 3,010 ± 560 N in the flexed, neutral position to 5,470 N in the extended, abducted position. Further, there was a large position-dependent variation in the ratio of fracture initiation force to the peak axial force. The initiation of fracture was 83% of the peak axial force in the extended, abducted position, but the ratio was 34% in the extended, adducted position. Conclusions. This may have significant implications for the development of pelvic injury criteria by automobile designers attempting to mitigate pelvis injuries.

BIOFIDELITY EVALUATION OF DYNAMIC AND STATIC RESPONSE CHARACTERISTICS OF THE THOR LX DUMMY LOWER EXTREMITY

Abstract This study evaluates the biofidelity and response characteristics of the Thor Lx dummy lower extremity prototype. Static and dynamic tests were performed to evaluate its response relative to that of cadavers and the Hybrid III (45° dorsitlexion ankle and soft joint stop). Static tests determined the ankle joint moment properties, ankle/tibia axial stiffness, and the mass and moments of inertia. The three different limbs were subjected to two different types of dynamic tests: pure dorsiflexion and a combination of dorsiflexion and axial load. The results show that the response characteristics of the Thor Lx better reflect those of the cadaver limbs, which indicates that the Thor Lx design is an improvement over the Hybrid III. The continuous ankle joint stiffness eliminates joint property discontinuities at the extreme ranges of motion, and the non-concentric joint locations of the Thor Lx mimic the ankle and sub-talar joints in the human. The Achilles tendon of the Thor Lx serves as passive musculature and increases ankle stiffness in dorsitlexion. A compliant element in the tibia shaft gives more biotidelic tibia axial load characteristics, and the straight shaf eliminates artificial moments created by axial loading. With its design modifications and comprehensive instrumentation package, the Thor Lx is capable of providing a more complete and biofidelic assessment of lower limb response and injury risk.

The Tibia Index: A Step in the Right Direction

Leg injuries are frequent occurrences for occupants involved in automobile crashes. This paper investigates the efficacy of a proposed injury criterion, the tibia index, to predict fractures of the leg. Using an interaction formula, the tibia index combines the applied compressive force and moment to predict mid-shaft fractures of the tibia and fibula. Quasistatic and dynamic test data of the leg are reviewed in an effort to establish critical threshold values of force and moment. The data indicate that there is minimal dependence of the fracture threshold on the direction of applied moment and suggest that a resultant moment is appropriate for the index. Meanwhile, axial loading of the leg results in bending of the tibia due to the curvature of the limb and eccentricity of the load through the ankle and knee. Since the distal and proximal ends of the fibula and tibia are weaker than the shaft, a supplemental compressive criterion is required for these regions. Validation of proposed indices relative to published experimental testing shows good correlation for dynamic results and verifies the dependence of the fracture threshold on an interaction between the applied moment and compressive force. Until additional testing can be conducted to generate injury risk functions, individual investigators must decide whether the static or dynamic criteria are most applicable for their test environment. Furthermore, implementation of the indices into dummy designs requires biofidelic response in order to provide accurate estimates of the injury risk.

A Protocol System for Testing Biohazardous Materials in an Impact Biomechanics Research Facility

This article presents a protocol system, comprised of a review process and a series of checklists, that was developed for testing cadaveric tissue in an impact biomechanics research facility. The use of cadaveric tissue may expose personnel to bloodborne pathogens including HIV and hepatitis B, which have been shown to remain virulent in a cadaver for several weeks after death. To minimize exposure risks, the protocol system presented emphasizes initial blood screening to keep infectious tissue from entering the laboratory, and adopts universal precautions to prevent exposure by treating all tissue as though it were infected. All lab employees must read, sign, and demonstrate proficiency in the protocol. Well-developed test procedures for the handling of biohazardous materials along with an annual individual protocol review have proven effective for the past 6 years in minimizing exposure risks.

Evaluation of energy-absorbing materials as a means to reduce foot/ankle axial load injury risk

Current restraint systems, such as seatbelts and airbags, have been developed mostly to protect the head and thorax during frontal crashes. They do not necessarily have equivalent effciency for lower extremities because of other loading factors such as the interaction between the foot and toepan or pedals. A relatively high frequency of foot and ankle injuries in combination with high morbidity warrants research into injury countermeasures. An energy-absorbing aluminium honeycomb was investigated as a means of load reduction during a simulated frontal impact with toepan intrusion. Test surrogates included human cadavers, a 50th percentile male Hybrid III leg with 45° dorsiflexion ankle and soft joint stop and a 50th percentile male Thor-Lx/HIIIr. Inclusion of an energy absorber between the cadaver heel and intruding footplate reduced tibia axial loads by as much as 39 per cent compared to cases without an energy absorber. Dummy results were compared to the human response and the Thor-Lx appeared to be more biofidelic than the Hybrid III.

A PNEUMATIC AIRBAG DEPLOYMENT SYSTEM FOR EXPERIMENTAL TESTING

This paper examines an originally designed airbag deployment system for use in static experimental testing. It consists of a pressure vessel and valve arrangement with pneumatic and electric controls. A piston functions like a valve when operated and is activated pneumatically to release the air in the tank. Once released, the air fills the attached airbag. The leading edge velocity can be controlled by the initial pressure in the tank, which can range up to 960 kPa. Three different test configurations were studied, which resulted in leading edge deployment speeds of approximately 20 m/s, 40 m/s, and 60 m/s. In experiments using this system, seven types of airbags were tested that differed in their material, coating, and presence of a tether. Data for each series of tests is provided. In addition to cost savings, the primary advantage of this system is its ability to quickly change the internal pressure. For the covering abstract see IRRD 893297.

Response of the Thor-Lx and Hybrid III Lower Extremities in Frontal Sled Tests

The objectives of this study were to evaluate and compare the responses, repeatability, and durability of the Thor-Lx/HIIIr and Hybrid III/Detention lower impacts in frontal sled tests. The effectiveness of the two limb types was studied in this study by evaluating responses in different test configurations using existing and proposed Injury Assessment Reference Values (IARVs) for both leg designs. Hybrid III or Thor-Lx legs were attached to the distal femurs of a 50 degree percentile male Hybrid III dummy, which was subjected to three series of 56 km/h frontal sled tests with and without toepan intrusion. Because of the design differences, many of the absolute response values were different between the Hybrid III and Thor-Lx legs. The expanded measurement capabilities, modified geometry and refined responses of the Thor-Lx limbs provide a more thorough and conservative judgment of injury risk. The Thor-Lx legs produced repeatable results throughout the series of tests and demonstrated sufficient durability under the severe loading conditions.