A Madymo Model of the Foot and Leg for Local Impacts 99SC12

It has been reported that lower extremity injuries represent a measurable portion of all moderate-to-severe automobile crash- related injuries. Thus, a simple tool to assist with the design of leg and foot injury countermeasures is desirable. The objective of this study is to develop a mathematical model which can predict load propagation and kinematics of the foot and leg in frontal automotive impacts.

A multi-body model developed at the University of Virginia and validated for blunt impact to the whole foot has been used as basis for the current work. This model includes representations of the tibia, fibula, talus, hindfoot, midfoot and forefoot bones. Additionally, the model provides a means for tensioning the Achilles tendon.

In the current study, the simulations conducted correspond to tests performed by the Transport Research Laboratory and the University of Nottingham on knee-amputated cadaver specimens. These tests include non-destructive local dynamic impact to the heel and toes of the foot. For each test, the loads registered at loadcells implanted in the mid-tibia and in the Achilles tendon, the accelerations registered at the impactor accelerometer, and the kinematic response was compared to their counterparts in the model.

In order to improve the model response to the local and blunt impact test data, a more biofidelic shape of the hind and midfoot, a distal-to-proximal translation capability at the ankle joint, and modified contact properties were included in the model. Other model parameters that were found to significantly influence the load propagation are the ankle and subtalar joint location, the configuration of the midtarsal joint and the knee joint properties. In addition, the impact location, foot initial state and level of Achilles tension influenced the model response.

The conclusions are that the model now is valid in local impacts to the foot and still maintains validity in blunt impacts to the foot. Thus the model can potentially improve our understanding of the load distribution in the foot and leg and of the foot and leg injury mechanisms, which in turn can help improve injury risk assessment.