Effects of lower limb torsion on ankle kinematic data during gait analysis.

VICON Clinical Manager software is widely used for gait analysis and has four methods for computing ankle plantarflexion-dorsiflexion motion and transverse plane ankle rotation profiles. The authors evaluated 14 subjects with a diagnosis of spastic cerebral palsy and tibial torsion ranging from 39 degrees internal torsion to 90 degrees external torsion, using the four different processing methods. It was found that clinically measured tibial torsion >20 degrees external or >15 degrees internal led to significant differences in the calculated ankle plantarflexion-dorsiflexion and transverse plane ankle rotation measurements between the four methods. Pearson correlations indicated that these differences increased with increasing external or internal tibial torsion. The variability was enough to affect conclusions of published articles and clinical decision making.