Kinematics of the equine back: a method to study the thoracolumbar flexion-extension movements at the trot.

This study was conducted to evaluate a method for quantifying the flexion-extension movements of the back of horses trotting on a track in the conditions of the clinical lameness examination. Using a 3-D kinematic analysis system, the successive positions of four markers placed at regular intervals between the withers and the tuber sacrale were recorded. To isolate the flexion-extension movements of the back, the positions of these four markers were recomputed in a trunk-related co-ordinate system of the horse. Then, for each frame, the equation of the third-order polynomial that best fitted the position of the four markers was determined. Using these equations, it was then possible to interpolate the vertical displacement of any point situated between the withers and the tuber sacrale. The accuracy of this method was evaluated using three additional markers placed between the four previous ones. The vertical displacements of these three markers were recorded and compared to the interpolated displacements provided by this method. The results showed that the experimental and interpolated values did not present any statistical difference except in the lumbar region. In this region, the general shape of the vertical displacement curve was conserved but magnified by 17%. This study showed that despite the weakness of the range of the flexion-extension movements of the equine back at trot, these movements can be quantified with reliability. This method was then used on a lame horse. The results obtained demonstrated the usefulness of this method to study the flexion-extension movements of horses suffering from various locomotor disorders.