Gait Graph Asymmetry Index
Gait Graph Asymmetry has been defined as the difference observed between the left and the right side gait analysis graph curves of the subject measured.
Although asymmetry is evident in many subject's gait analysis graphs, no quantification tools existed to enable the objective evaluation. The degree of Asymmetric behavior between the two limbs is a significant factor related to pathology and should be regularly evaluated. Thus, there is a need to evaluate the asymmetry observed in the gait analysis graphs that corresponds to normal and pathological characterizations.
Figure 1. Instant gait asymmetry is defined as the distance between the Left (red) and the Right (blue) curves.
In the above figure a significant distance between the Right (blue) and the Left (red) gait curves can be observed indicating an asymmetric involvement with the left knee more flexed than the right knee through out the gait cycle.
Gait Graph Asymmetry Index was developed with the same calculation concept of the Gait Graph Deviation Index. For measuring Asymmetry the differences between the Right and Left side gait curves are used in the calculation.
The concept behind using the green area (Normal Standard Deviation) that is used for the calculation of the Deviation indexes also for calculation of the Asymmetry Indexes is based on the following facts:
Normal curves have been created by including both sides (left &* right) so the inherent asymmetry of the normal subjects is incorporated in the Normal Subject's Standard Deviation
In clinical practice, if one of the limb curves follows exactly the Normal mean values ad the other curve would follow the borders of the Normal SD range, this would not be considered a pathological behavior.
Note: The convention used in the calculations, is to subtract Left Side values from the Right Side values.
Gait Graph Asymmetry Index is a measure that summarizes the observed instant asymmetry in the gait analysis graphs in a single number, using as unit of measurement the Normal Standard Deviation.
For the implementation of the index, a series of calculation steps are required. The calculation steps that are needed to create the Gait Graph Asymmetry Index are described here.