Angular orientations derived from a portable media device to assess postural stability during quiet standing in the horse

Background: Body-mounted sensors have been increasingly popular to measure horse movement with the majority of investigations examining linear movement. Many of these devices can also determine angular orientations, and measuring angular movements may increase the ability to differentiate treatment conditions. Objective: To determine if angular orientations utilising the sensors within a portable media device (PMD) could be used to differentiate stance conditions in standing horses. Study design: Cross-over. Methods: A PMD was mounted over the withers (thoracic vertebra 8-10) using a surcingle. Seven healthy horses were examined during quiet standing, and five trials were collected in a square stance, base-narrow stance, and at 5 and 10 min following sedation with xylazine hydrochloride (IV). Angular orientations around the mediolateral (ML), craniocaudal (CC), and vertical axes, and range of motion and standard deviations (SD) were extracted. Mixed-model ANOVAs, with stance condition as a fixed effect and horse as a random effect, were performed with significance at P<0.05. Results: There was no significant difference in any angular orientation variable when comparing the base-narrow to square stance condition. At 5 minutes following sedation with xylazine hydrochloride, there were significant differences in the range of motion and SDs for all three angular orientations (pitch, roll and yaw) compared to square stance (P < 0.005). At 10 minutes following sedation with xylazine hydrochloride, there were significant differences in the range of motion and SDs, respectively, for rotation around the ML (pitch) (0.91 degrees, 0.21 degrees) and CC (roll) (1.07 degrees, 0.25 degrees) axes compared to square stance (pitch: 0.71 degrees, 0.16 degrees; roll: 0.73 degrees, 0.18 degrees) (P < 0.036). Main limitations: No gold standard was utilised to determine the accuracy of the angular orientations. Conclusions: Use of angular orientations derived from sensors within the PMD may be another avenue for evaluating horses' postural sway during stance.