this gives the appearance of an ipsilateral forelimb lameness. Although there is
significant variability from horse to horse that is likely dependent on the type of
primary lameness, even slight primary hind limb lameness may cause compensatory
movement in the head that mimics obvious forelimb lameness. Frequently, the
apparent asymmetric head movement may be more easily seen than the asymmetric
vertical pelvic movement caused by the primary hind limb lameness. This implies
that the primary hind limb lameness may be easily missed because the
compensatory but false forelimb lameness is more apparent. The increased
sampling frequency of the inertial sensors compared to the unaided human eye
decreases the chance of this confusion considerably.
The second part of the law of sides is slightly misleading. Primary forelimb lameness
frequently causes compensatory movements in the vertical movement of the pelvis
attributable to both hind limbs such that false hind limb lameness can be measured
in both sides. Primary forelimb lameness causes the horse to shift its center of
gravity slightly toward the caudal half of the body during the stance phase of the
affected forelimb. This causes the pelvis to fall more in the contralateral hind limb
compared to the ipsilateral hind limb, mimicking impact-type lameness in the
ipsilateral hind limb. However, in addition a horse with a primary forelimb lameness
will not push off the simultaneously weight bearing contralateral hind limb as strongly
as usual. Strong propulsion from this contralateral hind limb would shift weight
forward during push-off onto the painful forelimb. Thus a horse with a primary
forelimb lameness will tend to push off the simultaneously weight bearing
contralateral hind limb with less force than usual, causing the pelvis to rise less. This
gives the appearance of a push-off type lameness in the contralateral hind limb. So,
the second part of the old ‘Law of Sides’ is only partially true, as primary forelimb
lameness may cause compensatory movements that mimic ipsilateral hind limb
impact-type lameness but contralateral hind limb push-off-type lameness. Confusion
between a false hind limb lameness and a true forelimb lameness, however, is not
so likely, since in most horses the primary forelimb lameness will need to be
considerable before the asymmetric vertical pelvic movement is easily seen by the
human eye. However, compensatory pelvic movement patterns with primary
forelimb lameness are regularly measured with the increased sensitivity of the inertial
sensors and these patterns are useful for helping to detect and evaluate forelimb
lameness.
Using Lameness Locator® to Quantify Response to Flexion Tests
Lameness Locator® can be used to objectively quantify the effect of flexion tests. A
positive response to flexion is then ascertained by simply comparing the amplitude of
the lameness values for that limb before and after flexion: the increase in
DIFFMAXHEAD and/or DIFFMINHEAD or their VS for forelimb flexion, or the
increase in DIFFMAXPELVIS and/or DIFFMINPELVIS for hind limb lameness.
Increases of approximately 6 mm (for DIFFMAXHEAD and DIFFMINHEAD) and 3
mm (for DIFFMAXPELVIS and DIFFMINPELVIS), which is the approximate 95%
confidence interval for random change, is a reasonable threshold value for
proclaiming a positive test.
Proceedings
of
the
South
African
Equine
Veterinary
Association
Congress
2016
39