If the pain of lameness peaks in the first half of stance, powerful neck muscles
reduce force of weight bearing by restricting the fall of the head. The head falls less
during the stance phase of the lame limb so that the head height from the ground
during the stance phase of the lame limb is higher than that during the stance phase
of the sound, or less lame, limb. This creates a difference in minimum head height
from the ground between the limbs (DIFFMINHEAD). If, on the other hand, the pain
of lameness peaks in the second half of stance, neck muscle activity reduces force
on the limb by raising the head during push-off. This creates a difference in
maximum head height from the ground between the limbs (DIFFMAXHEAD).
Forelimb lameness is reported by Lameness Locator® in a graphical display of a ray
diagram with DIFFMAX head on the x-axis and DIFFMIN head on the y-axis and by
calculating 4 lameness values.
Detecting Hind limb Lameness with Lameness Locator®
Reduction of force on the painful hind limb is accomplished either by falling with less
acceleration, rising with less acceleration, or both. If the first half of hind limb stance
is painful to the horse, different mechanisms are utilized, like shifting weight forward
or spreading the force of weight bearing out over a longer duration, that cause the
pelvis to fall less. It will stop falling sooner so that its lowest height will be higher
from the ground than if there was no hind limb pain in the first half of stance. This
results in a difference in minimum pelvic height between right and left hind limb
stance, which is measured by Lameness Locator™ as DIFFMINPELVIS.
If pain is in the second half of stance, the horse will push off the affected hind limb
with less force, thrusting the whole pelvis upwards less. This results in a difference
in maximum pelvic height between push-off of the right and left hind limbs, which is
measured by Lameness Locator™ as DIFFMAXPELVIS. Although one aspect
(impact or push-off) may be greater than the other, many horses with hind limb
lameness display components of both types of lameness.
Hind limb lameness is reported in a graphical display that depicts deficiency of right
and left hind limb impact (first half of stance) or push-off (second half of stance) and
by calculating 4 lameness values.
Detecting Compensatory Lameness with Lameness Locator®
In trotting quadrupeds, a primary lameness in the cranial half of the body will cause
compensatory movements in the caudal half of the body and vice-versa, such that an
apparent multiple limb lameness is present. Interpretation of these compensatory
movements is often interpreted by using the ‘law of sides’ (Buchner et al. 1996). The
first part of the ‘law of sides’ states that an apparent ipsilateral lameness, i.e.,
forelimb and hind limb lameness on the same side of the body, is likely due to
primary hind limb lameness with a compensatory but false forelimb lameness. The
second part of the ‘law of sides’ states that an apparent contralateral lameness, i.e.,
forelimb and hind limb lameness on opposite sides of the body, is likely due to a
primary forelimb lameness with a compensatory but false hind limb lameness.
Experimental studies have determined that the first part of the law of sides is, for the
most part, true. Increased force of weight bearing on the simultaneously landing
contralateral forelimb results in increased downward movement of the head.
Following the ‘lower-on-the-sound-side’ rule of head movement in forelimb lameness,
Proceedings
of
the
South
African
Equine
Veterinary
Association
Congress
2016
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