The viability of a three-dimensional forward dynamic model of walking as a research tool to enhance clinical understanding of gait abnormalities

Forward dynamic models are powerful tools which, alongside clinical gait analysis, can be used to evaluate abnormal walking conditions in a controlled environment to gain insight into movement adaptation strategies. This study explored the feasibility of using forward dynamic simulation models of walking to enhance clinical understanding of the link between pathological conditions and human walking patterns.

A 3D, forward dynamic single leg model of walking was developed using kinematic pelvis drivers to allow the reproduction of the entire stance phase of normal walking. The model simulated normal walking for the last 60% of the stance phase of gait successfully, but was unable to reproduce normal walking immediately after heel strike. Increases in model complexity including a 3D knee and complex ground contact model have improved upon existing models in literature. The use of pelvis kinematic drivers was rejected, and the incorporation of a second leg was recommended to increase the clinical relevance of this model.

Rotational malunion of the tibia (RMT) is a condition in which the distal end of the tibia is rotated with respect to the proximal end, about the long axis of the bone, due to improper healing following severe tibial fracture. RMT has been associated with gait adaptations and linked to non-physiological joint loading and osteoarthritis (Eckhoff, 1994). To augment a clinical study of RMT, the single leg walking model was evaluated for use in modelling RMT during the last 60% of stance phase. The single leg model was sensitive to geometric changes similar to RMT values. In addition, the model indicated similar trends to those seen in clinical data.

A new method for the quantification of model sensitivity to input parameters was developed. Using this method, the simulations of running and walking were more sensitive to muscle model and joint stiffness and damping parameters than the range of values in literature. In addition, the sensitivity of many model parameters was greater than the clinical changes due to RMT. These results stress the importance of the measurement of subject specific model parameters, particularly in clinical populations.

The research presented here provides tools to enhance the potential of forward dynamic walking models to contribute to the clinical evaluation of gait pathology.