Abstract
Differences in movement asymmetry between surfaces and with increasing speed increase the complexity of incorporating gait analysis measurements from lunging into clinical decision making. This observational study sets out to quantify by means of quantitative gait analysis the influence of surface and speed on individual-rein movement asymmetry measurements and their averages across reins (average-rein measurements). Head, withers, and pelvic movement asymmetry was quantified in 27 horses, identified previously as presenting with considerable movement asymmetries on the straight, during trot in hand and on the lunge on two surfaces at two speeds. Mixed linear models (p < 0.05) with horse as the random factor and surface and speed category (and direction) as fixed factors analyzed the effects on 11 individual-rein and average-rein asymmetry measures. Limits of agreement quantified differences between individual-rein and average-rein measurements. A higher number of individual-rein asymmetry variables—particularly when the limb that contributed to movement asymmetry on the straight was on the inside of the circle—were affected by speed (nine variables, all p ≤ 0.047) and surface (three variables, all p ≤ 0.037) compared with average-rein asymmetry variables (two for speed, all p ≤ 0.003; two for surface, all p ≤ 0.046). Six variables were significantly different between straight-line and average-rein assessments (all p ≤ 0.031), and asymmetry values were smaller for average-rein assessments. Limits of agreement bias varied between +0.4 and +4.0 mm with standard deviations between 3.2 and 12.9 mm. Fewer average-rein variables were affected by speed highlighting the benefit of comparing left and right rein measurements. Only one asymmetry variable showed a surface difference for individual-rein and average-rein data, emphasizing the benefit of assessing surface differences on each rein individually. Variability in straight-line vs. average-rein measurements across horses and exercise conditions highlight the potential for average-rein measurements during the diagnostic process; further studies after diagnostic analgesia are needed.
Highlights
In addition to presenting a horse in hand, on the straight, in the symmetrical gait of trot [1] horse movement is commonly assessed on the lunge during the equine lameness or poor performance examination [2, 3]
It was hoped that differences in asymmetry measures between surfaces [21] would be preserved by this operation, and presenting average-rein data could be useful in reducing the complexity of interpreting gait analysis data in clinically lame horses: being faced with too much information may lead to suboptimal decisions [22]
The baseline mean absolute values of pelvic movement asymmetry in the present study (Table 1) are higher than the values in 37 clinically hind limb lame horses that showed a significant reduction in movement asymmetry after diagnostic analgesia [25], further supporting the assumption that these asymmetries might not be a result of daily variation
Summary
In addition to presenting a horse in hand, on the straight, in the symmetrical gait of trot [1] horse movement is commonly assessed on the lunge during the equine lameness or poor performance examination [2, 3]. The more the amount of body lean angle increases, the higher the speed and smaller the circle [5]. This behavior can be predicted from the increasing centripetal force (Fcentri = mv2/r; m = mass, v = forward velocity, r = circle radius) and the assumption that the horse aims at minimizing extrasagittal joint torques. In non-lame or mildly lame horses, visual assessment appears to be affected little by the measurable increase in movement asymmetry on the circle [6]. Referred or compensatory movements [7] may contribute to confusions during visual observation of horses on the lunge [8]
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