Page 170 - Adams and Stashak's Lameness in Horses, 7th Edition

136 Chapter 2

considered, with “lowest on sound” for both head and torso with decreased downward movement of the head
pelvic movement for fore‐ and hindlimb lameness, as an and pelvis and decreased upward movement of the pelvis
VetBooks.ir total vertical movement with these ipsilateral gaits tends “hip hike” and “hip dip” on the inside hindlimb). This
during and after inside forelimb and hindlimb stance (or
accurate indicator of side of lameness. However, the
might appear as inside forelimb and hindlimb lameness
to be less than the trot, with more rolling from side to
side than vertical movement up and down. So, although, to an observer evaluating vertical movement of the head
in principle, vertical movement of the head and pelvis for forelimb lameness and vertical movement of the pel­
should be good indicators of lameness, they may be vis or rotation of the pelvis for hindlimb lameness. 41,46,47
more difficult to observe. Certainly, also, the compensa­ These characteristics of asymmetry should be consid­
tory lameness patterns for ipsilateral gaits will be differ­ ered when evaluating horses for lameness at the lunge.
ent than that for the contralateral trot. More information Also, it has been shown that even normal horses trained
of lameness in gaited breeds can be found in Chapter 9. to lunge will frequently move in one direction differently
than in the other direction. 8,46 This increased variability
makes detecting lameness at the lunge more complicated
EVALUATION OF LAMENESS AT THE LUNGE compared to straight‐line evaluation. Disagreement
between veterinarians of the existence, side, and ampli­
Evaluation for lameness during the lunge, on either tude of lameness observed during the lunge is higher
soft or hard ground, is thought to exacerbate and bring than that for evaluation of lameness in the straight line.
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out lameness that may not be seen when the horse is mov­ However, if horses show consistent lameness during a
ing in a straight line. Moving in a circle, because the torso straight‐line trot, they will most commonly show lame­
and limbs are tilted relative to ground surface, alters the ness in the same limb during the lunge on the same sur­
distribution of ground reaction forces both within a sin­ face and rarely only in the opposite side limb.
gle limb and between right and left limbs. However,
because the torso is tilted relative to the ground, 24,25 there
is normal asymmetrical peak vertical forces between the EVALUATION OF LAMENESS UNDER SADDLE
inside and outside limb 14,17 and normal vertical move­
ment of both the head and pelvis. 41,46 These asymmetries Some veterinarians believe that a lameness evaluation
must be appreciated and understood as normal. Large that does not include evaluation under saddle is incom­
horses, small diameter circles, and high speed of move­ plete. Certainly, evaluation for lameness under circum­
ment will exacerbate these asymmetries. It has also been stances and in surroundings that are far removed or
determined that the amplitude and characteristics of ver­ different from the usual and expected activity of the
tical head and pelvic asymmetries are dependent on type horse may fail to expose the true abnormality, adversely
of ground surface on which the horse is lunged, and affecting performance of the horse. In some environ­
because of high normal horse‐to‐horse variability, an ments, for example, in a large arena with an appropriate
asymmetry observed in one direction should not be iden­ surface, evaluation for lameness under saddle is easier
tified as abnormal until lunging in the other direction is and in many cases preferred. This is especially true for
also observed. However, deviations from these known some breeds that do not trot regularly unless under sad­
asymmetric patterns can be used and analyzed to help dle. However, evaluation for lameness under saddle is
locate or confirm lameness to a particular limb. not always practically available to the veterinarian, and
On soft surfaces the outside limbs are less efficient at it should not be expected that lameness under saddle
turning and propulsion because the foot digs into the would always be worse or more visible than lameness
soft surface as the limb is pushing off the ground. When without a rider. Although the extra weight and back
the outside forelimb is pushing off, the horse is essen­ extension may induce more pain, the influence of the
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tially changing direction. On soft ground that “gives rider and excitement of the horse may serve to mask
way,” changing direction is less efficient. Therefore, on lameness. Rider position and activity can also create
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soft ground, the head is thrown upward during pushoff artifactual (i.e. “false”) lameness that will interfere or
of the outside forelimb, assisting the horse in changing confuse veterinary examination for clinical abnormality.
direction toward the inside of the circle. This might A rider properly sitting the trot, in synchrony with the
appear as an outside forelimb pushoff‐type lameness to horse’s vertical torso movement, will create the least arti­
some observers. Similarly, pushoff of the outside facts on the observed lameness. A rider posting (perform­
hindlimb is less efficient, but this causes the pelvis to rise ing a rising trot) moves forward and upward when one
less, making the horse appear to have an outside hindlimb forelimb (usually the inside limb if riding in circle) is
lack of vertical propulsion. Also, the pelvis, tilted toward weight bearing and then backward and downward when
the middle of the circle of movement, falls less during the same‐side hindlimb is pushing off. The effect of the
weight‐bearing of the inside hindlimb, mimicking an upward and forward movement is increased weight‐bear­
impact‐type hindlimb lameness. If using pelvic rotation ing on one forelimb, which, if that limb is painful, could
instead of VPM to detect hindlimb lameness, these char­ worsen the perceived lameness in that limb. However, the
acteristics would appear as “hip hike” on the inside backward and downward movement during pushoff of
hindlimb and “hip dip” (if this can indeed be seen) on the the same‐side hindlimb (the inside hindlimb when riding
outside hindlimb. The veterinarian must then determine in a circle) will frequently blunt or reduce the expected
if the inside hindlimb “hip hike” and the outside hindlimb pelvic rise. This effect will tend to create what appears to
“hip dip” are the same lunging in the other direction. be a lack of opposite hindlimb propulsion, a false lame­
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On hard surfaces, asymmetries of vertical head and ness in a normal horse. Effects of posting and moving
pelvic movement are primarily related to rotation of the in a circle are frequently additive and, depending on the