Page 185 - Adams and Stashak's Lameness in Horses, 7th Edition

Examination for Lameness 151

method is a very conservative assessment where 100% limb, but has yet to have localized the origin of lameness
improvement is rare but small changes in amplitude of within the limb. In many studies blocking of the defini­
VetBooks.ir method is a more liberal assessment with 100% improve­ but did not eliminate the lameness, and the locomotion
tive primary source of lameness significantly decreased
lameness are unlikely to be misinterpreted. The second
of the horse after diagnostic analgesia is not always
ment more common, but where small changes of ampli­
tude of mild lameness may be seem exaggerated. identical to that of a non‐lame horse. This suggests that
The first method is calculated as follows: it is more appropriate than to compare the after block
evaluation to the evaluation done immediately before
IS before block IS after block the block evaluated, instead of comparing to the trial
IS before any blocks were applied.
before block When using inertial sensors to evaluate lameness, one
where IS is inertial sensor measure. will soon realize that the level of lameness, especially in
The second method is calculated as follows: the beginning of the evaluation, may not be stable.
Lameness can increase, decrease, switch limbs, or change
in timing at the beginning of a lameness evaluation.
IS before block IS after block Beginning a series of blocking procedures before the
IS before block IS threshold lameness is stabilized risks misinterpretation and misdi­
agnosis. When using inertial sensors to evaluate response
where threshold is an experimentally determined value to blocking, it is recommended to first stabilize the lame­
of the confidence interval of the inertial sensor measure ness by some movement (walking) or exercise (light
in a group of horses thought not to be lame by experts lunging on soft surface) and to avoid strong joint flex­
during full lameness evaluations. ions or deep palpations of limb structures before assess­
For example, a horse with a Diff Max Pelvis before ing for lameness. Lameness can be considered stabilized
block of +12 mm and a Diff Max Pelvis of +6 mm after when the amplitude (±8.5 mm for head and ±3 mm for
block would have a 33.3% improvement in lameness pelvic movement asymmetry), limb(s) involved, and tim­
((12 – 8)/12 = 0.33…) using the first method and a 66.7% ing of lameness are consistent in back‐to‐back trials
improvement in lameness ((12 – 8)/(12 – 6) = 0.66…) conducted within a few minutes of one another.
using the second method. Preference for method will
depend on characteristics of the individual case, including
beginning amplitude of lameness, stride‐by‐stride and (if Evaluation of Lameness During the Lunge
known) trial‐by‐trial variation of lameness, and whether Lameness Locator® can be used to objectively quan­
the lameness is a single or multiple limb lameness. It tify lameness while the horse is trotting in a circle. Some
should be noted that any percent improvement above lameness conditions in horses are more apparent when
100%, or that switches to the other limb, is interpreted as the horse is moving in a circle. Reference ranges and
an elimination of lameness, when in reality some pain on confidence intervals established for trotting in a straight
weight‐bearing may still be present. Also, at the time of line and collecting at least 25 contiguous strides, how­
this writing, this software considers any improvement ever, are not applicable. When the horse is trotting in a
below 25% improvement as no improvement. circle, the torso and limbs are tilted toward the center of
There is some evidence that regional nerve blocks in the circle. Depending on the horse, its speed of move­
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non‐lame horses do not appreciably change gait, do not ment, the radius of the circle it is moving in, and the
make the horse appear subjectively to be lame, and do characteristic of the surface, this tilt can be significant.
not significantly alter vertical ground reaction forces. Also, on soft surfaces, the circular movement, centripe­
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However, regional limb blocks in the front limb have tal forces, angle, and inclination of the limbs relative
been shown to prolong stance and the transition from to the ground cause less efficient outside limb pushoff,
braking to propulsion, supportive evidence that some and this creates normal asymmetric movement. However,
proprioceptive deficit or loss is induced. 19,37 When using the effects of tilt and surface characteristics can be indi­
inertial sensors to evaluate blocking, users may measure vidually predicted and accounted for. 59
subtle changes in lameness that are less or not apparent On soft surfaces, because the outside forelimb is less
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when relying on subjective evaluation. For example, it efficient during pushoff (the surface gives way to the
is not uncommon, in fact it is usual, for lameness to get forelimb pushing off), the horse will throw its head
worse (increase in amplitude) when a limb is blocked in upward and inward to assist in turning. Likewise the
an area that is below or does not include the anatomic outside hindlimb is less efficient at pushoff with the out­
structure or area with pain. In other words, blocking a side hindfoot digging into the surface. Subsequent pelvic
normal part of a painful limb will increase lameness. rise from this less efficient pushoff is less than after push­
This effect is increased with successive blocks that do off of the inside limb. Also, the torso tilting toward the
not include the focus of pain. Although blocking a nor­ inside of the circle results in less downward fall of the
mal limb in a horse without lameness has not been head during inside forelimb stance and of the pelvis dur­
shown to significantly affect force plate results, kine­ ing inside hindlimb stance (decreased downward move­
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matic evidence suggests lower limb loading. If lameness ment of the inside head and pelvis is independent of type
increases with the blocking of normal limbs or with the of surface). So, on soft surfaces, there is an appearance of
blocking of normal parts of limbs displaying lameness, an outside forelimb pushoff‐type lameness (right going
then one cannot expect a total removal of lameness to left and left going to right), an outside hindlimb push­
when the causative focus is finally found. Having lame­ off‐type lameness, and an inside hindlimb impact‐type
ness increase after a block is a good sign that the evalu­ lameness. These patterns of asymmetry should be
ator has picked the correct limb as the primarily lame expected when lunging on soft surfaces (Figure 2.144).