B. Johan Ivarsson

Injury tolerance and moment response of the knee joint to combined valgus bending and shear loading.

Valgus bending and shearing of the knee have been identified as primary mechanisms of injuries in a lateral loading environment applicable to pedestrian-car collisions. Previous studies have reported on the structural response of the knee joint to pure valgus bending and lateral shearing, as well as the estimated injury thresholds for the knee bending angle and shear displacement based on experimental tests. However, epidemiological studies indicate that most knee injuries are due to the combined effects of bending and shear loading. Therefore, characterization of knee stiffness for combined loading and the associated injury tolerances is necessary for developing vehicle countermeasures to mitigate pedestrian injuries. Isolated knee joint specimens (n=40) from postmortem human subjects were tested in valgus bending at a loading rate representative of a pedestrian-car impact. The effect of lateral shear force combined with the bending moment on the stiffness response and the injury tolerances of the knee was concurrently evaluated. In addition to the knee moment-angle response, the bending angle and shear displacement corresponding to the first instance of primary ligament failure were determined in each test. The failure displacements were subsequently used to estimate an injury threshold function based on a simplified analytical model of the knee. The validity of the determined injury threshold function was subsequently verified using a finite element model. Post-test necropsy of the knees indicated medial collateral ligament injury consistent with the clinical injuries observed in pedestrian victims. The moment-angle response in valgus bending was determined at quasistatic and dynamic loading rates and compared to previously published test data. The peak bending moment values scaled to an average adult male showed no significant change with variation in the superimposed shear load. An injury threshold function for the knee in terms of bending angle and shear displacement was determined by performing regression analysis on the experimental data. The threshold values of the bending angle (16.2 deg) and shear displacement (25.2 mm) estimated from the injury threshold function were in agreement with previously published knee injury threshold data. The continuous knee injury function expressed in terms of bending angle and shear displacement enabled injury prediction for combined loading conditions such as those observed in pedestrian-car collisions.

Dynamic Response Corridors of the Human Thigh and Leg in Non-Midpoint Three-Point Bending

Current standards and test devices for pedestrian safety are developed using results from impact tests where inertial considerations have dominated and the vehicle pedestrian loading environment has not been properly replicated. When controlled tests have been conducted to evaluate the biofidelity of anthropometric test devices, current designs have faired poorly. The objective of the current study was to develop dynamic force-deflection and moment-deflection response corridors for the 50 th percentile adult male thigh and leg subjected to non-midpoint 3-point bending at rates characteristic of the vehicle-pedestrian loading environment. Six thigh and eight leg specimens were harvested from eight adult male human cadavers and ramped to failure in dynamic 3-point bending in the latero-medial direction. All thigh specimens and four of the leg specimens were loaded at a point located one third of the femoral/tibial length from the distal end, whereas the point of load application for the remaining four leg specimens was at one third of the tibial length from the proximal end. Following geometrical scaling of the structural responses to the size of the 50 th percentile adult male, force-deflection and moment-deflection response corridors were determined using a procedure specifically designed for developing corridors from sets of individual responses for which the independent variable is displacement. The corridors provide necessary information for development and validation of mechanical and computational tools for evaluation of countermeasures for pedestrian lower extremity protection.

Influence of Age-Related Stature on the Frequency of Body Region Injury and Overall Injury Severity in Child Pedestrian Casualties

Objective. The current study aims to evaluate the influence of age-related stature on the frequency of body region injury and overall injury severity in children involved in pedestrian versus motor vehicle collisions (PMVCs). Methods. A trauma registry including the coded injuries sustained by 1,590 1- to 15-year-old pedestrian casualties treated at a level-one trauma center was categorized by stature-related age (1–3, 4–6, 7–9, 10–12, and 13–15 years) and body region (head and face, neck, thorax, abdomen and pelvic content, thoracic and lumbar spine, upper extremities, pelvis, and lower extremities). The lower extremity category was further divided into three sub-structures (thigh, leg, and knee). For each age group and body region/sub-structure the proportion of casualties with at least one injury was then determined at given Abbreviated Injury Scale (AIS) severity levels. In addition, the average and distribution of the Maximum Abbreviated Injury Score (MAIS) and the average Injury Severity Score (ISS) were determined for each age group. The calculated proportions, averages, and distributions were then compared between age groups using appropriate significance tests. Results. The overall outcome showed relatively minor variation between age groups, with the average ± SD MAIS and ISS ranging from 2.3 ± 0.9 to 2.5 ± 1.0 and 8.2 ± 7.2 to 9.4 ± 8.9, respectively. The subjects in the 1- to 3-year-old age group were more likely to sustain injury to the head, face, and torso regions than the older subjects. The frequency of AIS 2+ lower extremity injury was approximately 20% in the 1- to 3-year-old group, but was twice as high in the 4- to 12-years age range and 2.5 times as high in the oldest age group. The frequency of femur fracture increased from 10% in the youngest group to 26% in the 4- to 6-year-old group and then declined to 14% in the 10- to 15-years age range. The frequency of tibia/fibula fracture increased monotonically with group age from 8% in the 1- to 3-year-old group to 31% in the 13- to 15-year-old group. Conclusions. While the overall outcome of child pedestrian casualties appears to be relatively constant across the pediatric stature range considered (∼74–170 cm), subject height seems to affect the frequency of injury to individual body regions, including the thorax and lower extremities. This suggests that vehicle safety designers need not only account for the difference in injury patterns between adult and pediatric pedestrian casualties, but also for the variation within the pediatric group.

Biofidelity Improvements to the Polar-II Pedestrian Dummy Lower Extremity

This paper is from the SAE World Congress & Exhibition, held in April 2007 in Detroit, Michigan, USA. Part of the Pedestrian Safety session, this paper reports on a study of pedestrian kinematics with the Polar-II Finite Element Model, used to evaluate the biofidelity of the lower extremity components of the pedestrian dummy. The authors evaluated this biofidelity in lateral impact loading corresponding to a 40 km/h pedestrian-car collision. The authors focused on the bending moment-angle response from a newly developed knee joint, dynamically loaded in four-point valgus bending; this joint was compared against previously published postmortem human subject (PMHS) response values. In addition to the stiffness characteristics of the knee joint, individual ligament forces were also recorded during the bending tests. In another component of the study, lower extremity long bones developed for improved anthropometrical accuracy and deformability were dynamically loaded in latero-medial three-point bending. The final part of the study used a biofidelity rating system to evaluate the modified Polar-II lower extremity components. The authors conclude that the Polar-II Finite Element model accurately replicates the PMHS response under loading conditions similar to a pedestrian-car collision.