Unilateral-Dominant Lameness Induces Changes in Breakover Duration Symmetry in Equine Walk

Lameness is widely regarded as the most prevalent problem affecting equines globally. Much is understood about the adjustment of upper body posture to reduce loading in an affected limb. However, the relationship between lameness and breakover duration, when the distal limb experiences high tensile stresses, remains an underinvestigated area. Thus, this study aimed to investigate breakover duration at walk in a cohort of horses, quantifying the effect of fore- and hindlimb lameness. It was hypothesized that lameness would induce an asymmetry between breakover durations of affected contralateral limb pairs. Breakover durations of sixteen horses (five sound and eleven lame, as presented by owners) were measured using data collected by hoof-mounted gyroscopes. Breakover durations of the limbs of contralateral pairs were compared, and paired Student's t-tests were used to determine whether differences were significant (p < 0.01). A high degree of symmetry was seen in breakover durations of sound horses, with a mean (SD) duration of 168(19)ms and a negligible mean absolute difference (6ms, p = 0.07). In lame horses, breakover durations of lame limbs (167(22)ms) were longer than those of contralateral limbs (146(23)ms, p < 0.001); and breakover durations of the ipsilateral (160(26)ms) and diagonal (162(24)ms) limbs were equivalent and comparable to those of sound limb pairs. These results indicate that where there is lameness present in a contralateral limb pair, there will be a breakdown in the symmetry of breakover duration, with the most severely affected limb having a significantly longer breakover duration than the contralateral. This pattern should be investigated in the future as a marker to indicate lameness.