As improvements in vehicle safety decrease the number of crash fatalities, research in extremity injury is becoming increasingly important (Lund and Ferguson, 1995). Lower extremity injuries, while generally not life threatening, can cause severe impairment and permanent disability. The pediatric population is especially sensitive to these injuries due to potential damage to growth plates and developmental delays during long recovery periods (Winthrop et al, 2005). Currently, little is known about the nature of pediatric lower extremity injuries. This area is lacking due to the deficiencies of pediatric Anthropomorphic Test Devices (ATDs) and the infrequency of pediatric Post Mortem Human Subject (PMHS) testing.
The following two studies provide a basis for pediatric lower extremity investigation. In the first study, a pediatric ATD was subjected to knee bolster airbag deployments. The results indicated that long bone injury was possible due to axial tibia loads over 2.5 kN and bending moments over 70 Nm in certain seating positions. In addition, the study revealed important limitations of the ATD itself, such as insufficient instrumentation and the lack of biofidelity of the ankle joint. The results also highlighted the importance of using accurate injury threshold data for pediatric extremities.
The second study addresses the need to develop injury criteria directly from pediatric tissue specimens. Pediatric tibiae will soon be available for testing, but the specimens will not be accompanied by surrounding musculature or the fibula. Adult PMHS studies have established that these structures affect the bending strength of the long bones (Kerrigan et al, 2003; Rupp et al, 2008). This study evaluates the difference in mechanical properties between adult tibiae with naturally attached musculature and fibulae vs. artificially attached musculature without fibulae. Three-point bend tests indicate that the artificial attachment of musculature and the absence of the fibula may not affect the accuracy of some injury parameters, specifically fracture force and fracture moment. However, there was a difference between groups in fracture time and time dependent parameters such as fracture energy. These results indicate that pediatric tibia testing may be possible without the natural muscular attachments of the leg or the fibula.