ASYMMETRY IN PLACEMENT OF BILATERAL SKIN MARKERS ON HORSES AND EFFECTS OF ASYMMETRIC SKIN MARKER PLACEMENT ON KINEMATIC VARIABLES

Objective-To evaluate asymmetry in placement of bilateral skin markers on horses and to determine effect of asymmetric skin marker placement on kinematic variables for trotting horses. Animals-10 horses for eva luation of asymmetry in marker placement; 1 horse for evaluation of ef fects on kinematic variables. Procedure-Asymmetry in marker placement was assessed by attaching markers to horses and comparing radiographs of left and right limbs. An experimental model was developed to determ ine effects on kinematic variables; accuracy of the model was validate d experimentally. Using kinematic data from a clinically normal trotti ng horse as reference data, effects of asymmetric marker placement on vertical displacement-time and joint angle-time diagrams were determin ed by use of the model. Results-Asymmetry of placement was < 1 cm for markers on the distal portions of the limbs and < 2 cm for markers on the proximal portions. Asymmetric marker placement did not alter gener al shapes of the vertical displacement-time and joint angle-time curve s. In most instances, largest differences in vertical displacement att ributable to asymmetric marker placement were equal to or less than ma gnitude of the asymmetry of placement. Alterations in joint angle-time curves were mainly a result of shifting of the curves on the Y axis. Joint range of motion was only slightly changed by asymmetric marker p lacement, but maximum flexion and extension angles were greatly altere d. Conclusions and Clinical Relevance-Some kinematic variables can be greatly altered by small differences in skin marker placement. Such ef fects should be taken into account when evaluating kinematic data for sound and lame horses.