Page 174 - Adams and Stashak's Lameness in Horses, 7th Edition

140 Chapter 2

words, the horse pushes off with less vertical force but parts of the stride will become asymmetric. Kinematics,
with more horizontal ground reaction force in the sec­ like kinetics, can be used to quantify absolute movement
VetBooks.ir instrument. Variability between trials in controlled con­ most applications quantify lameness by measuring the
measures that may correlate well with lameness. However,
ond half of stance.
The stationary force plate is a precise and accurate
asymmetry of movement between left and right sides of
ditions is low (coefficients of variation below 10%), and the body. Many different motion parameters have been
sensitivity is high enough to detect subclinical lame­ studied and used to detect and evaluate forelimb and
ness. However, acquiring data requires controlled con­ hindlimb lameness in horses, including vertical move­
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ditions. The hoof must strike completely within a ment of the torso (head bob, pelvic fall and rise), stride
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relatively small area, often requiring multiple attempts. and step length and timing, pelvic rotation (hip hike
Speed of movement is controlled, both to increase the and dip), 44,56 limb and hoof flight pattern, and joint
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chance of successful hoof strike and to decrease variabil­ angle extremes and range of motion. Asymmetric verti­
ity between hoof strikes. The stationary force plate is cal movement of the torso, because it is more directly
considered by some to be a gold standard for objective associated with vertical ground reaction force, is the
lameness evaluation in horses, but the controlled condi­ most sensitive kinematic indicator of lameness. 14,16,31
tions required for acquiring consistent results make it The body motion changes of lameness are more vari­
unlikely to be adopted for routine use in clinical prac­ able stride by stride than changes in ground reaction
tice. Although it varies with breed, the forelimb of horses force. High stride‐by‐stride variability of lameness low­
that are not lame trotting across the force plate at mod­ ers the signal (lameness) to noise ratio, rendering it more
erate speed will strike the force plate with vertical force difficult to detect small amplitudes of lameness or small
approximately equal in magnitude to 100% of its body changes in amplitude of lameness. Variability can be
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weight. The hindlimb of normal horses trotting across decreased by strictly controlling conditions of evalua­
the force plate at slow to moderate speed will strike with tion. Alternatively, or in addition, the adverse effect of
vertical force equivalent to about 90% of body weight. stride‐by‐stride variation can be minimized by collecting
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Induction of “subtle,” mild, and moderate lameness data from a high number of contiguous (one after the
decreased vertical ground reaction force in horses trot­ other) strides. Despite the higher variability compared
ting on a treadmill by 4%, 9%, and 24%, respectively. to the force plate, results of kinematic evaluation of
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Horses with AAEP grade 4 lameness will strike the fore­ lameness are generally more intuitive and easy to under­
limb with a force as low as 50% of body weight. stand for the veterinary practitioner. The practicing vet­
erinarian can more easily apply significant findings in
MEASUREMENT OF MOVEMENT (KINEMATICS) kinematic studies of lameness in their standard lameness
evaluation techniques.
Kinematics is the measurement and study of move­ The original kinematic technique was camera based.
ment. Limb and torso pain alters the normal movement The horse is filmed while moving and body motion is
of the horse. If pain predominates in one side of the body, quantified by analyzing trajectories of markers attached
the normal symmetric movement between right and left to the body of the horse (Figure 2.129). Computer

Figure 2.129. Marking of the horse with reflective spheres (head, right hoof walls, pelvis) for camera‐based kinematic evaluation
of lameness.