Naturally-occurring forelimb lameness in the horse results in significant compensatory load redistribution during trotting.

This study aimed to quantify the compensatory response to naturally-occurring forelimb lameness on load redistribution. Data from lameness investigations using an inertial sensor based system to monitor the response to forelimb diagnostic anaesthesia were reviewed. Horses with primary forelimb lameness were grouped for analysis as (1) all horses combined (n= 28), (2) forelimb-only lameness (n= 8/28), (3) forelimb-contralateral hindlimb lameness (n= 14/28), (4) forelimb-ipsilateral hindlimb lameness (n= 6/28). The effect of diagnostic anaesthesia on measures of head and pelvic movement asymmetry was determined using the Wilcoxon signed rank test. Spearman's correlation analysis was performed between forelimb and hindlimb variables. Statistical significance was set at P< 0.05. Forelimb diagnostic anaesthesia resulted in a decrease in pelvic movement asymmetry among all horses and the forelimb-only and forelimb-contralateral hindlimb lameness groups. Pelvic movement asymmetry associated with the contralateral hindlimb decreased by a median of 38% (interquartile range [IQR] 10-65%), 43% (IQR 28-60%) and 28% (IQR 12-67%) in all horses, forelimb-only and forelimb-contralateral hindlimb groups respectively (P< 0.05). Maximum pelvic height difference (PDMax) significantly decreased in all horses combined and the forelimb-contralateral hindlimb lameness group by a median of 66% (IQR 24-100%) and 78% (IQR 27-100%, P< 0.01), respectively. Change in head movement asymmetry and vector sum was significantly positively correlated with PDMax in all horses combined and the forelimb-contralateral hindlimb group (P< 0.05). Forelimb lameness had a significant effect on hindlimb and pelvic movement in horses with clinical lameness resulting in compensatory load redistribution and decreased push-off from the contralateral hindlimb.