Effect of a unilateral hind limb orthotic lift on upper body movement symmetry in the trotting horse

Abstract

In trotting horses, movement asymmetry is associated with ground reaction force asymmetry. In humans, limb length differences influence contralateral force production. Here we investigate whether horses, in immediate reaction to limb length changes, show movement asymmetry adaptations consistent with reported force differences. Aim of this study was to quantify pelvic and compensatory head and withers movement asymmetry as a function of limb length changes after application of orthotic lifts. In this experimental study movement asymmetry of eleven trotting horses was calculated from vertical displacement of poll, withers, sacrum and left and right tuber coxae with inertial sensors. Horses were assessed in-hand under 5 conditions (all with hind limb boots): without orthotic lifts, and with a 15mm or 30mm orthotic lift applied to the left hind or right hind. A linear mixed model investigated the influence of orthotic lift condition (P<0.05, pairwise posthoc Bonferroni correction). Pelvic movement asymmetry showed increased pelvic downward movement during stance of the shorter limb and increased pelvic upward movement during and after stance of the longer limb (P<0.001) with asymmetry changes of 3-7mm (4-10mm) for 15mm (30mm) lifts. Hip hike (tuber coxae movement asymmetry) was unaffected (P = 0.348). Head and withers movement asymmetry were affected less consistently (2 of 3 respectively 1 of 3 head or withers parameters). The small sample size of the study reduced generalizability, no direct force measurements were conducted and only immediate effects of orthotic lifts were assessed with no re-assessments days or weeks after. Conclusions about mechanical consequences (weight bearing, pushoff) are based on published movement-force associations. Pelvic movement asymmetry with an artificial change in limb length through application of an orthotic lift indicates increased weight support with the shorter limb and increased pushoff with the longer limb. This may be of relevance for the management of horses with different hoof shapes between contralateral limbs, for example some chronically lame horse.

Asymmetries of horses walking and trotting on treadmill with and without rider

“…However, some level of kinematic and kinetic asymmetries is often found in sound, well‐performing horses in both walk6,7 and trot8‐11 with considerable overlap being reported between low‐grade lameness and normal horses 12. Laterality, defined as a systematic preference to use one side of the body as a consequence of cerebral lateralisation,13 is discussed as one possible cause for locomotor asymmetries in healthy horses, but other possible factors are conformation,14 trimming and shoeing,15 training16 and pathological or age‐related changes. Vertical movement asymmetry increased only marginally in sound trotting horses after the addition of lead weights to the saddle and the rider,17 whereas horses became more asymmetrical with a professional rider vs a novice rider of similar bodyweight 18.…”

The Effect of Tungsten Road Nails on Upper Body Movement Asymmetry in Horses Trotting on Tarmac

“…The prominence of the road nail on the underside of the shoe effectively creates a very small lengthening of the limb with the nail compared to the contralateral limb. The effect of artificially lengthening one hindlimb -termed 'orthotic lift' -has been investigated previously using the same approach as used here: upper body movement symmetry based on IMU measurements [28]. Interestingly, midline pelvic (sacrum) movement asymmetry was shown to be affected by lengthening, while tuber coxae movement asymmetry (HHD) was not [28].…”

“…The effect of artificially lengthening one hindlimb -termed 'orthotic lift' -has been investigated previously using the same approach as used here: upper body movement symmetry based on IMU measurements [28]. Interestingly, midline pelvic (sacrum) movement asymmetry was shown to be affected by lengthening, while tuber coxae movement asymmetry (HHD) was not [28]. This is opposite to the findings of the present study, where HHD was affected by the presence of a road nail but midline pelvic movement asymmetry parameters (PDmin, PDmax, PDup) were not.…”

Effect of induced hindlimb length difference on body-mounted inertial sensor measures used to evaluate hindlimb lameness in horses

“…It is possible that hindlimb length asymmetry does not create the same artefactual effect (a measured lameness caused only by limb length asymmetry) on measures of hindlimb lameness associated with pelvic rotation (hip hike, hip dip). Hip hike was not affected when elevation was placed on one hindlimb and horses were evaluated trotting in a straight line (8).…”

“…The effect of hindlimb length difference induced by hoof height elevation on equine hindlimb lameness has been initially studied by Vertz, et al in 2018, where it was found that minimum and maximum pelvic height differences, as measures of hindlimb lameness, were significantly influenced in horses trotting in a straight line. However, in this study the effect of hindlimb length difference was only evaluated in horses trotting in a straight line on hard surfaces, limited conditions compared to common clinical evaluation [8].…”