Development of a finite element model to study the effects of muscle forces on knee-thigh-hip injuries in frontal crashes.

A finite element (FE) model with knee-thigh-hip (KTH) and lower-extremity muscles has been developed to study the potential effects of muscle tension on KTH injuries due to knee bolster loadings in frontal crashes. This model was created by remeshing the MADYMO human lower-extremity FE model to account for regional differences in cortical bone thickness, trabecular bone, cortical bone with directionally dependent mechanical properties and Tsai-Wu failure criteria, and articular cartilage. The model includes 35 Hill-type muscles in each lower extremity with masses based on muscle volume. The skeletal response of the model was validated by simulating biomechanical tests without muscle tension, including cadaver skeletal segment impact tests documented in the literature as well as recent tests of seated whole cadavers that were impacted using knee-loading conditions similar to those produced in FMVSS 208 testing. Simulations of knee-to-knee-bolster impacts conducted with and without different levels of lower-extremity muscle activation reported in the literature for braking/bracing suggest that muscle tension has the potential to decrease the externally applied force required to cause KTH fracture, and the potential to increase the likelihood of femoral shaft fracture relative to hip fracture by increasing bending moments in the femoral shaft. However, more reliable and complete data on activation levels of muscles in the lower extremities during vehicle braking and bracing are needed before this effect of muscle tension can be confirmed and before the overall effects of muscle tension on KTH injury can be determined.