Page 984 - Adams and Stashak's Lameness in Horses, 7th Edition

950 Chapter 9

of fatal injuries in Thoroughbred racehorses found that hair coat, general disposition, and the presence of any
most were euthanized after a catastrophic injury to a current medical conditions as well as treatment thereof.
VetBooks.ir difference between forelimb affected. Conversely, there coupled with results from current diagnostic procedures
Recognition of previous lameness in the specific patient
forelimb; however, there was no statistically significant
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was a predisposition for right forelimb injury in the United
may raise the level of suspicion for a recurrent injury.
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Kingdom. In the United States, horses were more likely Racetrack practitioners who are familiar with their
to sustain fracture of the left forelimb during racing and patients have a number of advantages, including the
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right forelimb during training. Fractures of the proximal ability to perform multiple examinations either in hand
sesamoid bones were the most common injury in the or on the racetrack in the horse’s routine work environ­
United States, but Australian studies showed that fracture ment. A disadvantage of known history is the potential
of the front or rear cannon bone was most common dur­ for bias in diagnoses. Another disadvantage for the race­
ing racing, followed by accompanying fractures of the track practitioner is obstacles in the working environment
proximal sesamoid bones and proximal phalanx. 6,7 that may preclude a thorough locomotor examination.
Training and racing schedules have been scruti­ Special scheduling may be required to accomplish a
nized. 2,11–13,17–20,26 The risk of catastrophic injury and complete examination. The behavior of a fit racehorse
forced lay‐up in fit California Thoroughbred racehorses likewise limits the time allowed for the evaluation, in
was significantly increased following 2 months of high‐ addition to presenting an inherent safety hazard. Many
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speed exercise with distance accumulation. Two‐year‐ racehorses become rank and difficult to handle after
olds exceeding 0.76 furlongs/day, 3‐year‐olds exceeding only a few jogging sessions and may hide a subtle lame­
0.85 furlongs/day, and 4‐year‐olds exceeding 0.95 fur­ ness due to excitement. Diagnosis of a new injury may
longs/day were at higher risk of sustaining injury than be challenging if there are preexisting healed injuries
those working shorter distances. In another study, the that are not clinically active.
racing injury rates were inversely proportional to the Lameness may be displayed in a broad spectrum of
success of the individual trainer. The incidence of tibial clinical signs, ranging from behavioral changes, reluc­
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and pelvic stress fractures rises with increasing distances tance to train, and poor performance to mild or overt
cantered during a 30‐day training period but not over a gait alterations. It is common for horses to display
60‐day period. 40,58 changes in temperament, such as aggressive or passive
Track conditions also correlate with injury. 10,46 behavior, prior to displaying actual lameness. Horses
Fracture rates in Japan increased as dirt tracks became may become track sour or display changes during train­
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muddier and decreased as turf surfaces became softer. ing such as lugging in or out or running off. Other mani­
The differences between synthetic surfaces, dirt, and turf festations include reduced appetite, poor hair coat, soft
courses are still under investigation. One study showed palate displacement, or tying up.
a greater proportion of stress fractures detected on scin­ Lameness associated with pain is the manifestation of
tigraphic examinations from horses training on a syn­ an avoidance response. The character of lameness is
thetic surface (31.7%) compared with horses training largely determined by the location or source of an injury,
on a dirt surface (23.0%) at an earlier point in time. although it is difficult to differentiate exact foci of pain
Additionally, there were a greater proportion of pelvic or specific disorders based on gait alone. Generalities of
and tibial stress fractures diagnosed in horses from a gait combined with the rest of the clinical picture often
synthetic surface‐trained group than from the dirt‐ aid in lesion localization, but there are no absolutes
trained group. 34 based solely on gait.
Individual conformation has been recognized clini­ Gait alterations associated with mechanical limita­
cally to affect locomotion and long‐term soundness. 36,37 tions may be challenging to distinguish from lameness
Some traits have been shown to influence the onset of associated with pain. An example of characteristic gait
clinical abnormalities. For example, horses with offset patterns is a delay in contact of the foot with the ground
knees have an increased incidence of stress‐related dis­ (drift) caused by a foot bruise or developing abscess in a
orders of the knees and an increased risk of fetlock front foot; a similar problem in a hindfoot produces a
problems. Other flaws that likely predispose a horse to stringhalt appearance. Abduction of a limb prior to
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injury include back‐in‐the‐knee conformation and car­ ground contact is often observed with a fracture of the
pal or fetlock varus deviations. lateral wing of the coffin bone, incomplete lateral con­
dylar fracture, and fracture of the lateral aspect of the
carpus. Changes in advancement of a limb and stride
DIAGNOSIS OF LAMENESS length occur with many lameness conditions and vary
with location and severity. Horses with a humeral stress
History and physical evaluation, economics, and per­ fracture, high suspensory desmitis, or other proximal
sonal experiences help determine the appropriate diag­ limb injury do not advance the limb fully in the cranial
nostic steps for every horse. Knowledge of the exercise phase of the stride. Tibial stress fractures often display a
and racing schedule, including when fast work has taken limited contact or support phase of the stride, which
place, intensity level of training, and past performance is results in a jerking lift‐off of the limb in addition to a
important. It is also important to be aware of recent lay‐ limited cranial phase of the stride.
up, convalescence, and previous surgery. Diagnosis of lameness should be confirmed by isolat­
The physical evaluation is straightforward and basic, ing the source of lameness. Ancillary diagnostic anesthe­
but it must be thorough. It is especially helpful if the sia may be employed to localize the pain if necessary
veterinarian is familiar with the patient. The general and feasible. Diagnostic nerve blocks may be difficult to
health of the horse must be considered, including appetite, perform for two reasons: the fractious behavior of some