Knee injury thresholds are based on cadaver experiments and do not take into account active muscle contributions. Preliminary studies have indicated that muscle forces reduce injury risk in knee ligaments [Soni et al, 2006]. In this paper we study the effect of active muscle forces on knee bending angle and shear displacements for a free standing pedestrian in lateral impacts using PAMCRASH TM.
A passive FE model has been developed and validated for tests reported in Kajzer et al. (1997, 1999) and Kerrigen et al. (2003). An Active Lower Extremity Model for Safety (ALEMS) has then been developed by including forty seven lower extremity muscles. A-LEMS has then been used to simulate below knee and ankle impacts in free standing pedestrians with activated and deactivated muscles.
The FE model shows good correlation with both Kajzer’s and Kerrigan’s tests results. On incorporating active muscles, it is observed that ligament strains decrease, even though the Von Mises stresses in the bones do not show a significant difference. Knee bending angle and shear displacement curves also show lower peaks with active muscles.
We conclude that muscle activation reduces ligament strains, as well as knee bending angles and shear displacements. It suggests that knee injury thresholds can be different from those formulated on the basis of cadaver studies. Therefore muscle effects should be taken into account in deciding vehicle safety standards and injury predictions in pedestrian crashes.
In this study we have assumed a straight line of action for muscles. This can lead to errors for muscles which do not work along a straight line. Tendons should also been included for more accurate muscle modeling. Currently, the study is also limited to the standing posture only and other postures are being investigated.
The current study investigates the effect of active muscle forces on the knee injury thresholds for a standing pedestrian.