Page 173 - Adams and Stashak's Lameness in Horses, 7th Edition

Examination for Lameness 139

OBJECTIVE ASSESSMENT OF LAMENESS

VetBooks.ir kevin G. keeGan

The standard of practice to detect and assess severity
of lameness in horses is observing the horse in motion
with the naked eye and then scoring using a discrete
scale, for example, the AAEP or UK lameness scales/
grades. This is sufficient for some cases. However, clini­
cal studies strongly suggest that detection and evalua­
tion of lameness in horses using the naked eye is
insufficient in many cases, especially when the severity
of lameness is mild. 22,25,30,33,45 Multiple limb involvement
and compensatory movement in the opposite half of the
body, and observation of different movement parame­
ters, contribute to variability in assessment. Agreement,
even between experts, for the detection of mild lameness
between AAEP grades 1 and 2 or for picking the most
affected limb is only slightly above chance. The most
30
likely explanation for this is limited temporal resolu­
tion of the human eye to detect fast events and small Figure 2.127. Stationary force plate set for evaluation of
51
amounts of asymmetry in the movement of the horse. lameness in horses. White line outlines approximate area of top of
Furthermore, unblinded subjective assessment is predis­ force plate, which is embedded into the ground and covered with a
posed to bias. Objective assessments of lameness by rubber mat to prevent shying. Source: Courtesy of Dr. Michael
1
precise and accurate measurement of ground reaction Schoonover at Oklahoma State University.
force or asymmetry of movement at high sampling rates
can be used to mitigate these limitations. 100 V 10
MEASUREMENT OF GROUND REACTION FORCES max H max
(KINETICS) 80

Most diseases that cause lameness do so because of H zcI 5
pain during weight‐bearing. A horse will bear less weight 60 H minI
on an affected limb to decrease pain, resulting in Percentage of body weight (vertical GRF) H auc+ 0 Percentage of body weight (horizontal GRF)
decreased ground reaction force, which can be objec­ 40 H auc– H maxI
tively measured. The stationary force plate, force‐meas­ V maxI
uring treadmill, force‐measuring devices attached to the –5
bottom of the hoof, and pressure‐sensitive mats have 20 H min
been used to measure ground reaction forces in moving V auc1 V auc2
horses. 4,5,8,9,17,18,20,23,26–29,35,46,47,49,50,53,68,71,73–75 The stationary
force plate is the most commonly used and cited method. 0 –10
During an evaluation for lameness with the stationary Time (s)
force plate, the horse is moved over the force plate so Figure 2.128. Stationary force plate data (from a single hoof strike)
that at least one, and preferably just one, hoof strikes the of relevance for determination of lameness. V = peak vertical ground
max
force plate completely within the confines of the surface reaction force. V = vertical impulse (force × time) in first half of stance.
auc1
of the force plate (Figure 2.127). Ground reaction forces V auc2 = vertical impulse (force × time) in second half of stance.
can be measured in all three directions—vertical, hori­ H = peak negative (deceleratory) horizontal ground reaction force in
min
zontal, and transverse (Figure 2.128). Decreased vertical first half of stance. H max = peak positive (acceleratory) horizontal ground
ground reaction force and, to some extent, altered hori­ reaction force in second half of stance. H auc− = deceleratory horizontal
zontal ground reaction forces are most often associated impulse. H auc+ = acceleratory horizontal impulse. V maxI = time index of
with lameness in the horse. Lower peak forces and V max . H minI = time index of H . H maxI = time index of H max . H = time index
min
zcl
impulse (area under the force vs. time curve) are associ­ of horizontal ground reaction force cross over from deceleratory to
ated with increasing severity of lameness. It is also likely acceleratory force. No transverse forces are shown.
that the shape of the vertical and horizontal ground reac­
tion force curves contains information relevant to deter­ decreased deceleratory horizontal ground reaction force,
mining timing of lameness and differentiating whether and decreased vertical ground reaction impulse in the
pain is maximum during limb impact, in the first half of first half of stance. Horses with reduced hindlimb pro­
8
stance or during pushoff, in the second half of stance. 5,20,75 pulsion, or decreased pelvic rise after hindlimb pushoff,
It has been shown that horses with an impact hindlimb have decreased vertical ground reaction impulse in the
lameness, or less movement of the pelvis downward, second half of stance and a conversion of vertical force
have decreased peak vertical ground reaction force, to acceleratory horizontal ground reaction force. In other