Kinematic symmetry index: a method for quantifying the horse locomotion symmetry using kinematic data.

This study was conducted to evaluate a method for quantifying locomotion symmetry at trot in sound and lame horses. Using a 3D kinematic analysis system, the kinematics of the limb joints of sound and lame horses were recorded. The differences in motion between the left and right homologous joints were then quantified using a symmetry index based on an inter-correlation method. This method was used to calculate the symmetry indices of the vertical displacements and angle-time diagrams of the joints of each horse. In order to evaluate the sensitivity of this method of quantifying the locomotion symmetry, the symmetry indices of horses suffering from the three main types of lameness (forelimb, hind limb and bilateral lamenesses) were compared with those calculated for a reference group of clinically sound horses. The symmetry indices calculated using this method were sensitive enough to distinguish different degrees of lameness. Except for symmetrical bilateral lameness, the indices obtained also allowed us to determine which of the fore or hind limbs were lame. The results of this study make it possible to consider potential applications of this method in research and clinical fields.