The effect of tibial torsion on the dynamic function of the soleus during gait.

An induced acceleration analysis (IAA) model was used to investigate the effect of tibial torsion on the ability of the soleus to support and propel the body during gait. The IAA approach is well suited for this study because it allows soleus action to be quantified in the presence of varying amounts of tibial torsion, while other factors such as body configuration and muscle activation are held constant. The results of the analysis showed that excess tibial torsion shifts the induced knee joint accelerations toward flexion, valgus and external rotation, and diminishes body center-of-mass support and propulsion. This analysis supports the concept that bony mal-alignment can lead to 'lever arm dysfunction'. The objective data correlate with previous clinical observations related to valgus stress, crouch and the role of the soleus in level walking. The IAA model provides a tool for examining various aspects of abnormal gait independently and quantitatively.