Linear Discriminant Analysis for Investigating Differences in Upper Body Movement Symmetry in Horses before/after Diagnostic Analgesia in Relation to Expert Judgement

Abstract

Diagnostic analgesia and lunging are parts of the equine lameness examination, aiding veterinarians in localizing the anatomical region(s) causing pain-related movement deficits. Expectation bias of visual assessment and complex movement asymmetry changes in lame horses on the lunge highlight the need to investigate data-driven approaches for optimally integrating quantitative gait data into veterinary decision-making to remove bias. A retrospective analysis was conducted with inertial sensor movement symmetry data before/after diagnostic analgesia relative to subjective judgement of efficacy of diagnostic analgesia in 53 horses. Horses were trotted on the straight and on the lunge. Linear discriminant analysis (LDA) applied to ten movement asymmetry features quantified the accuracy of classifying negative, partial and complete responses to diagnostic analgesia and investigated the influence of movement direction and surface type on the quality of the data-driven separation between diagnostic analgesia categories. The contribution of movement asymmetry features to decision-making was also studied. Leave-one-out classification accuracy varied considerably (38.3–57.4% for forelimb and 36.1–56.1% for hindlimb diagnostic analgesia). The highest inter-category distances (best separation) were found with the blocked limb on the inside of the circle, on hard ground for forelimb diagnostic analgesia and on soft ground for hindlimb diagnostic analgesia. These exercises deserve special attention when consulting quantitative gait data in lame horses. Head and pelvic upward movement and withers minimum differences were the features with the highest weighting within the first canonical LDA function across exercises and forelimb and hindlimb diagnostic analgesia. This highlights that movement changes after diagnostic analgesia affect the whole upper body. Classification accuracies based on quantitative movement asymmetry changes indicate considerable overlap between subjective diagnostic analgesia categories.

Changes in Head and Pelvic Movement Symmetry after Diagnostic Anaesthesia: Interactions between Subjective Judgement Categories and Commonly Applied Blocks

“…In the present study, we have quantified changes in head and pelvic movement symmetry with inertial measurement units before and after diagnostic anaesthesia in 179 horses undergoing clinical lameness examinations at a single referral hospital. Previous studies into compensatory patterns during straight-line and circular trotting [4,[6][7][8][9][10] have evaluated patterns across a number of block "types" or in relation to the overall movement symmetry changes. The present data-driven, retrospective study aimed at investigating whether different commonly utilized "types" of forelimb and hind limb diagnostic anaesthesia elicit different asymmetry change patterns associated with alterations in weight-bearing and push-off, and as a function of three subjectively expert-assigned "efficacy" categories (negative, partially positive, positive [5]).…”

“…While potentially different for forelimb lameness, differences in how individual horses adapt their body lean angle have been shown after hind limb diagnostic anaesthesia [16], which may mask any DPDmax effect when studied across straight-line and circular trotting. When using linear discriminant analysis for studying the effects on movement symmetry of the same three "efficacy" categories used here [9], it is interesting to note that DPDmax gets assigned the highest weight in the first discriminant function for straight-line trot. However, DPDmax is relegated to 7th place (out of 10) overall and to as low as 8th or 9th place for the inside and outside rein on hard ground when measured on the lunge.…”

“…The sign convention used for the seven movement symmetry measures utilizes negative values for horses with left lameness and positive values for horses with right lameness. For combining data from diagnostic anaesthesia administered to the left and right limbs without the effects of opposite sides canceling out, the following procedure was implemented in accordance with previously published work [8,9]. First, the differences ("Delta" values) between the corresponding symmetry values before and after diagnostic anaesthesia were calculated (Delta = value after − value before ), rendering negative values for horses with improved symmetry after diagnostic anaesthesia of the right limb, i.e., smaller positive values after administration of the block compared to before.…”

“…For example, does the desensitization of different anatomical areas or structures result in different movement patterns of the horse, and how is this reflected in the judgement of veterinary experts? Furthermore, analysis of clinical lameness cases indicates that the "law of sides" also applies during circular movement (on the lunge) across hard and soft surfaces [8,9]. Linear discriminant analysis suggests that a differentiation between the three "efficacy" categories is supported by circling on a hard surface for forelimb lameness and on a soft surface for hind limb lameness [9].…”

“…Furthermore, analysis of clinical lameness cases indicates that the "law of sides" also applies during circular movement (on the lunge) across hard and soft surfaces [8,9]. Linear discriminant analysis suggests that a differentiation between the three "efficacy" categories is supported by circling on a hard surface for forelimb lameness and on a soft surface for hind limb lameness [9]. Interestingly, across different types of anaesthesia, this datadriven approach also shows that data clusters for the three "efficacy" categories show the least amount of separation for straight-line, in-hand trotting.…”