Page 467 - Adams and Stashak's Lameness in Horses, 7th Edition

Diagnostic Imaging 433

SPECIFIC APPLICATIONS FOR LAMENESS change in the thermal pattern of the hoof wall is useful
in recognizing laminitis. Generally, the coronary band is
DIAGNOSTICS
VetBooks.ir The Examination 1–2 C warmer than the remainder of the hoof. An
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inflammatory problem is indicated when the hoof begins
to approach the temperature of the coronary band.
If thermography is to be used, all bandages and leg
wraps should be removed 2 hours before the examina­ Thermography can also be very beneficial in the pro­
tion. The horse should be thoroughly brushed to remove gressive evaluation of the contralateral limb where sup­
any dirt and debris. Thermography is best performed port limb laminitis is potential sequelae. Thermography
after the clinical examination has been performed makes it possible to detect inflammation in the
(including watching the horse move, palpation, and contralateral foot well before lameness is evident.
manipulations) but before nerve or joint diagnostic Preventative therapy can therefore be instituted sooner
analgesia. The horse is brought into a covered area away in the course of disease and hopefully before the lamini­
from direct sunlight and any breezes. A 10‐minute accli­ tis is irreversible. The chronic phase is characterized by
matization period is allowed, and then a systematic progressive displacement of the third phalanx. The ther­
examination of the horse is performed using the thermo­ mal image is the opposite of the acute phase. As the cof­
graphic camera. 15 fin bone displaces, the vasculature is pulled further away
The camera is positioned 90° to the area of interest, from the surface causing the thermal image to appear
and the sequential images are taken. The limbs are progressively cooler. That is, the coronary band is more
examined from all four directions, the neck from both difficult to distinguish from the remainder of the hoof
sides (ventrally), the torso from both sides (dorsally and wall. Finally, the post‐chronic phase is seen when the
ventrally), the shoulders from the front and both sides, laminae have healed, but vascular changes (damage)
the hips from both sides and the back, and the head persists secondary to coffin bone displacement. Thermal
from both sides (dorsally and ventrally). Each of the imaging can be useful to identify the vascular damage
images is then assessed in relation to the findings of the that has occurred. These will be areas of intense cold,
clinical examination of the horse. which will identify the areas of vascular damage.
Thermography is also an excellent method of evalu­
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The Foot ating the patient with palmar foot pain syndrome. The
author has never identified a consistent thermal pattern
Thermography of the hoof has been useful for the associated with these cases but has been able to charac­
diagnosis and evaluation of several conditions of the terize reduced blood flow to the caudal hoof and to
foot. 9,13,21 Laminitis, palmar foot pain, subsolar or sub­ identify thermal stresses associated with hoof imbalance
mural abscesses, corns, and any other inflammatory and superficial inflammatory disease. Thermography is
condition of the hoof are specific conditions where ther­ one of the few methods that can readily determine the
mography provides valuable information concerning relative blood flow to the palmar foot area. This is
the disease. Obviously, thermography is not needed to accomplished by evaluating the foot thermographically
definitively diagnose these problems. Thermography both before and after exercise. The normal horse will
does however provide additional information that is sustain a 0.5 C increase in temperature of the foot after
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helpful in localizing the problem, assessing the degree of exercise, but about 40% of horses with palmar foot pain
inflammation associated with it, and deciding the best syndrome will not sustain this increase in the caudal
course of treatment. Thermographic evaluation is par­ foot due to the low blood flow. This is in sharp contrast
ticularly helpful with early or occult conditions of the to other focal inflammatory conditions of the hoof such
foot, where the physical and/or radiographic examina­ as bruises, or fractures, which are characterized by focal
tion findings are inconclusive. areas of increased temperature that correspond to the
Normally, the coronary band is the warmest area of site of injury. Exercise in these cases intensifies the “hot
the leg, and because of this, inflammation of this area spot.”
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can be difficult to detect. The hooves should be thermo­ Hoof abscesses before they drain are often seen as
graphically compared in several ways. Comparisons relatively cold areas. This is due to the pressure caused
should be made between all four hooves, front to front by the abscess that decreases the circulation to the
and front to rear. A difference of more than 1 C between abscessed area. The hoof capsule is a closed environ­
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hooves is significant. In cases where all 4 feet are ment, and the swelling that occurs due to the abscess is
involved, comparisons of the hoof temperature with the seen thermographically as an abnormal cold area. Once
temperature of the area between the bulbs of the heel the abscess opens and the pressure is relieved, the cold
should be made. area changes to a hot area.
Laminitis is characterized by inflammation of the
laminar structures of the hoof. Laminitis can be divided
into four phases—developmental, acute, chronic, and Joint Diseases
post‐chronic—and each of the phases has characteristic Joint inflammation produces characteristic thermal
thermal information. The developmental stage has been patterns. The best view to study most joints is from the
studied thermographically the least. During the develop­ dorsal aspect. 13,23 Typically, the normal joint is cool com­
mental stage there are no clinical signs, but the thermal pared with the surrounding structures. An exception to
image changes. There are progressive periods of vaso­ this rule is the hock, which has a vertical “hot spot”
constriction followed by periods of profound vasodila­ along the medial aspect that corresponds to the saphen­
tation; the heat seen gets hotter and broader following ous vein (Figure 3.253). As a joint becomes inflamed,
each vasoconstrictive period. During the acute phase a the thermal pattern changes to an oval area of increased