Lungeing is part of the standard lameness examination, however it systematically affects movement symmetry even in sound horses. We evaluated a method for objective lameness detection on the circle accounting for this asymmetry bias.
Twenty-six horses undergoing lameness examination were equipped with inertial sensors (Xsens) on head, sacrum and tubera coxae. Asymmetry in vertical displacement was quantified for trot on straight line and circle using multiple measures. Horses were classified lame when falling outside the directional reference range of sound horses (directional = ‘normal’ margins and lame limb depending on rein and sign of measure). Objective classification on the circle was compared to subjective evaluation, final diagnoses and objective classification on the straight calculating the proportion of matches. Regression analysis evaluated the association of change in asymmetry between straight line and circle and baseline asymmetry on the straight.
The match between objective classification on the circle and the exact fore-/hindlimb(s) scored lame subjectively was 81% / 79%. The match with the diagnosed limb(s) was 71% / 85%. There was a high frequency of false positives compared to subjective evaluation. Objective evaluation on the circle added new information compared to assessment on the straight line in 70% (forelimb) / 58% (hindlimb) of instances (contralateral limb lame, bilateral lameness, lame on circle but sound on straight). Change in asymmetry was not associated with baseline lameness (P≥0.062).
Objective lameness evaluation on the circle makes a valuable contribution to patient assessment: e.g. subtle lameness falling within the margins of ‘normal’ on the straight or bilateral lameness could be identified. In future, the predictive value of the proposed technique should be determined.