Page 1055 - Adams and Stashak's Lameness in Horses, 7th Edition

Occupational‐Related Lameness Conditions 1021

Why Is Evaluating Lameness in Gaited Horses Different Gaited horses are often evaluated under saddle in
(More Difficult)? their regular environment. The extra weight of the rider
VetBooks.ir pelvis during the symmetric gaits other than the trot are therefore may help to exacerbate a mild lameness. They
and saddle will increase the ground reaction force and
The vertical movement trajectories of the head and
may also more easily maintain a consistent speed or gait
identical in concept to the trot, which means that they
move down during the first half and up during the second when ridden than when moved in hand.
half of stance. Therefore, the same principles of altered
movement with lameness apply, with “lowest on sound” TM
for both head and pelvic movement for fore‐ and hindlimb Using Body‐Mounted Inertial Sensors (The Q
lameness, as an accurate indicator of side of lameness. and Lameness Locator®) to Evaluate Lameness
Also, with the ipsilateral gaits, there is more rolling from in Gaited Horses
side to side than vertical movement down and then up. Gaited horses can be evaluated for lameness using
So, although in principle vertical movement of the head body‐mounted inertial sensors, but there are some
and pelvis should be good indicators of lameness, they unique characteristics for acquiring data and important
may be more difficult to observe. Certainly, the compen­ data interpretation facts that need to be understood
satory lameness patterns for ipsilateral gaits will be differ­ when using currently available systems.
ent than that for the contralateral trot. With the exception of the standard walk, any sym­
There are many reasons why gaited horses are more metrical gait that causes a falling and rising of the body
difficult to evaluate for lameness. The trot is the most twice per stride can be analyzed with body‐mounted
common gait of horses in the United States, and horses inertial sensors. This two‐phase, sinusoidal‐like vertical
that trot or pace have a suspension phase to their stride movement pattern, with downward movement of the
such that the relative impact is greater in horses that torso during the first half of stance (impact) and upward
trot or pace. Most equine lameness can be considered movement during the second half of stance (pushoff), is
weight‐bearing lameness, with a decrease in peak verti­ generally retained even with the four‐beat gaits like the
cal ground reaction force as the main effect. Therefore, fox trot (forelimb hits the ground slightly before con­
gaits with higher normal vertical excursion of the center tralateral hind limb, i.e. a broken trot) and the stepping
of mass, and higher vertical ground reaction forces pace (hindlimb hits the ground slightly before the ipsi­
experienced by the limbs, will more apparently display lateral forelimb, i.e. a broken pace). Measurement of
lameness. Horses that typically move in gaits without a head and pelvic trajectory and calculation of differences
clear suspension phase are more likely to mask low‐ in maximum (between the stances) and minimum
grade pain on weight bearing. (within the stances) heights remain valid for determin­
Those familiar with evaluating horses at a trot recog­ ing lameness. At the standard walk, with a cadence of
nize asymmetries of movement such as a head nod, hip 1–2–3–4 (LH, LR, RH, RF), and equal timings between
hike or hip drop, shortened stride, asymmetric hock footfalls, this biphasic vertical movement is shifted so
height, etc., as well as compensatory lameness (ipsilat­ that maximum torso heights are highest during stance
eral forelimb or contralateral hindlimb). Veterinarians and lowest between stances. Current software does not
must shift their thinking to evaluate gaits that fall in the include algorithms that detect this shift, and, therefore,
continuum between trot and pace. One way to do that is they are not valid for the walk. Data can be collected at
to separately evaluate the forelimb and hindlimbs. The the walking gaits, and an amplitude of asymmetry may
gaits are still symmetric, but they are asymmetric indeed be measured and reported, but the side and
between fore‐ and hindlimbs. The forelimbs should timing of lameness may not be accurate. However,
move symmetrically, and the hindlimbs should move weight‐bearing lameness is less measurable (and less vis­
symmetrically. Therefore, the evaluator may want to ible) at the walk than at the faster gaits, and the impor­
train their mind to look at each half separately. Some tance of measuring lameness at the walk is minimal.
gaited horses have an exaggerated head movement, but While it may appear that some lameness is better dis­
it still should be symmetric between right and left fore­ played at the walk than at other gaits, this is really only
limbs. Hindlimb lameness can be difficult to evaluate in because the movement is slow enough for the limited
gaited horses because they do not have a typical suspen­ temporal resolution of subjective observation to pick up
sion phase and therefore their hip movement or gluteal the movement disturbance. A horse demonstrating lame­
asymmetry may often be minimal compared with horses ness at the walk will have measurable lameness at the trot.
at a trot or pace. With the ipsilateral gaits (pace, stepping pace, etc.),
Due to the rapid movement of the limbs in some gaited hindlimb lameness analyses need to be flipped, i.e. left
horses, particularly for horses performing the rack, classic hindlimb lameness is a right hindlimb lameness and vice
fino gait, or the paso largo gait, the evaluator may wish to versa. This is because hindlimb footfall, which is cur­
improve their chances of identifying a lameness or asym­ rently determined by the right forelimb gyroscope and
metry in gait by having the horse travel over a hard sur­ the assumption that the horse is moving in a contralat­
face. The speed of limb movement is often near the eral gait, is one half‐cycle out of phase, i.e. right hindlimb
threshold of the human eye’s ability to accurately discrimi­ footfall is coded as left hindlimb footfall and vice versa.
nate movement and/or placement of the limbs. The combi­ Correct hindlimb footfall sequence can be accurately
nation of eyes and ears may help the evaluator identify the determined by pelvic rotation from the sensor on the
lameness or asymmetry. The sounding board used to show pelvis (generation 5 Q sensors include a three‐axis
TM
and evaluate Paso Fino horses can be used to help evaluate gyroscope), but as of the date of this writing, this has not
horses with a rapid gait. been fully tested and implemented in Lameness Locator
®