Caudal paw displacement during movement initiation and its implications for possible injury mechanisms.

Objectives: The purpose of this study was to quantify and determine the degree to which dogs experience negative displacement of the paw during movement initiation on natural surfaces, the frequency of that displacement, and whether or not the negative displacement could yield injuries. Methods: Seven retired racing Greyhound dogs were selected to participate in sprint starts on two natural (non-vegetated and vegetated) surfaces. Kinematic analysis was conducted to quantify the displacements. Results: All dogs in all trials experienced a negative paw displacement in at least one or more limbs. Significant effects were found for negative displacement across surfaces, limb, and for the surface x limb interactions. Rear paw negative displacement was -6.68 ± 2.55% body length (BL) for the non-vegetated surface and -5.29 ± 1.92% BL for the vegetated surface. Front paw negative displacement was -21.42 ± 2.62% BL for the non-vegetated surface and -17.25 ± 3.82% BL for the vegetated surface. There was no significant difference between average torso velocity on the two track surfaces. This study verified that the paw does negatively displace (moves backwards) during movement initiation. The magnitude of the displacements suggests that multiple injury mechanisms could be present. Clinical relevance: These findings demonstrate the extreme kinematics placed on the canine body during movement initiation, which might further the understanding of the mechanism of injury and contribute to enhanced surgical and rehabilitation techniques.