Page 168 - Adams and Stashak's Lameness in Horses, 7th Edition

134 Chapter 2

If attempts to lateralize the lameness do not success­
fully produce observable asymmetric movement, the
VetBooks.ir differentiating these from his/her memory bank of how a
evaluator must rely on absolute movement parameters,
normal horse moves. For bilateral forelimb lameness, a
diagonal advanced placement of the forelimb, with the
forelimb hoof hitting the ground before the contralateral
hindlimb (but this is normal in some breeds), and an over­
all suppression of vertical head movement (compared
with vertical movement of the torso) are sometimes appre­
ciated. For both bilateral forelimb and hindlimb lameness,
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a stiff, shuffling, and short appearing stride may be seen.
However, unless the norm of the horse before the onset of
lameness is known, this can be difficult to differentiate
from individual, idiosyncratic locomotion patterns.

OBSERVING MOVEMENT OF THE LIMBS
Many motion parameters have been measured and
studied as lameness indicators in horses, and there are
many limb movement parameters that have been associ­
ated with lameness. It is not unusual to find in the litera­
ture reports of kinematic studies in which many different Figure 2.125. (A) Fetlock extension and (B) coffin flexion angles
limb motion parameters were measured but few were during full weight‐bearing. With lameness (A) decreases and
found to be significantly associated with lameness. (B) decreases.
Although there is considerable overlap, there is also con­
siderable contradiction between studies as to which increased in either the lame or more lame hindlimb or in
motion parameters are sensitive indicators of lameness in the non‐lame or less lame contralateral hindlimb, 53,55
horses. Some difference can be explained by differences whereas relative stance duration as a percentage of total
in the models of lameness being studied. Despite these stride time and total stride time consistently decreases in
qualifications, there are some limb movement parame­ the lame or more lame limb. Diagonal advanced place­
ters that can be used as indicators of lameness in horses. ment, or initiating stance sooner in the limb diagonal to
However, high variability and low consistency, with some the lame limb (or ipsilateral limb for the rack and pace),
exceptions, make observing limb movement changes less may also be shortened. Step duration, or the time
critical for detecting and evaluating for lameness. between pushoff of one limb and impact on the con­
tralateral limb, on the other hand, is shorter between
JOINT ANGLE MEASUREMENTS ASSOCIATED pushoff of the lame and impact of the sound limb than
between pushoff of the sound limb and impact of the
WITH LAMENESS lame limb. However, stride timing variables are
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Decreased weight‐bearing due to lameness in the fore­ strongly dependent on speed of forward movement and
limbs or hindlimbs will decrease maximum fetlock training, which makes them less useful for detecting
extension and maximum coffin joint flexion during the lameness before and after blocking or treatment. 20
stance phase of the lame limb compared with the stance Stride length is shortened significantly only in moder­
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phase of the contralateral sound limb (Figure 2.125). 12,19 ate to severe lameness. Step length, or the distance
Maximum fetlock extension and coffin joint flexion dur­ between placements of opposite limbs, is less between
ing stance are sensitive indicators of both forelimb and placements of the lame and then sound limbs than
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hindlimb lameness in the horse. Fetlock extension during between placement of the sound and then lame limb.
lame limb stance was 8° less than sound limb stance in a Height of foot flight arc may be increased or decreased in
sole pressure‐induced lameness model of a grade 2 (out the lame forelimb compared to the sound forelimb, and
of 5) lameness. If fetlock joint angle could be detected the shape may be different, depending on the cause of
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sensitively and accurately, it would be an excellent visual lameness. Dragging the hindlimb toe is commonly
clue for the detection and evaluation of forelimb and thought to be a sign of subtle hindlimb lameness, but this
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hindlimb lameness. Carpal extension during stance is may not always be true. In the hindlimb, the height of
reduced but only with moderate to severe lameness. 28 hoof flight arc is determined by two competing factors
with the strongest determining the overall effect. Decreased
propulsion during pushoff of the lame hindlimb causes
STRIDE TIMING AND LENGTH VARIABLES the rear torso to rise less. In order to bring the affected
ASSOCIATED WITH LAMENESS limb forward during the swing phase of the stride without
dragging it on the ground, the proximal limb joints will
Stride timing variables (stance duration, swing dura­ flex more. The comparative extents of the decreased torso
tion, etc.) are relatively insensitive and inconsistent indi­ rise and increased limb flexion determine the height of the
cators of lameness. Unless the lameness is severe, when hoof flight arc. Amplitude of limb retraction is variable
stance time is shortened, stance time can be relatively depending on type of lameness and conditions of evaluation.
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