Page 478 - Adams and Stashak's Lameness in Horses, 7th Edition

444 Chapter 4

lameness may be more related to the specific cause(s) of secondary problem within the DIP joint in some horses
pain rather than the duration of the lameness. 84 with foot pain.
VetBooks.ir toe first and may occasionally stumble. 22,96,119 At a trot, useful to evaluate horses with foot pain. The wedge
While walking or trotting, many horses tend to land
Use of a wedge block, although nonspecific, can be
block allows perhaps more specific manipulation of the
horses with bilateral lameness tend to have a stiff shuf-
fling gait and often carry their heads and necks rigidly. distal limb than can be performed with flexion tests
This stilted gait is usually worsened when circled and (Figure 2.111). Elevating the toe, similar to a naturally
has been described as the horse “trotting on eggshells.” occurring negative palmar solar angle, is thought to
Owners often misinterpret this characteristic gait as an increase the strain on the DDFT and podotrochlear
unwillingness to advance the limbs associated with apparatus and increase the pressure on the navicular
shoulder pain. When circled in either direction on a hard bone and navicular bursa. Little work has been done to
surface, the lameness is usually exaggerated in the limb support the use of the wedge block, but in one study, toe
that is on the inside of the circle. The lameness and elevation tests resulted in a sensitivity of only 55% and
stilted gait is often exaggerated as the size of the circle is a specificity of only 42% for the presence of navicular
reduced. The horse may hold its head and neck to the pain. In contrast, raising the heels is thought to
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outside of the circle in an effort to reduce the amount of decrease the strain on the DDFT and podotrochlear
weight carried on the inside limb. One study reported apparatus and decrease the pressure on the navicular
that 20% of horses that presented with no overt signs of bone and navicular bursa. However, it will result in
lameness by owners displayed a bilaterally symmetrical increased heel pressure. One study found that heel eleva-
short‐stepping gait when evaluated by a veterinarian. tion had a sensitivity of 76% and a specificity of 26%
Asymmetric forelimb lameness was easily observed for the presence of navicular pain. The observation of
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when these horses were circled. This finding highlights worsening lameness following heel elevation has also
the importance of recognizing this type of gait in horses been observed in many horses with MRI‐confirmed
with bilateral forelimb lameness and the necessity to injury to the DDFT. 110
evaluate these horses on different surfaces and at the Wedge block manipulation of the distal limb typically
lunge. 84 consists of placing the foot on the block squarely in the
Hoof tester examination is considered essential for toe‐up position. The opposite limb is usually held up in
the clinical diagnosis of navicular disease/syndrome by a relaxed neutral position and held for 60 seconds. The
many clinicians. However, the reliability of this test is horse is then trotted off and any change in the lameness
somewhat controversial because a negative response to is observed and documented. The same test is then per-
hoof testers over the frog region is not uncommon in formed in the heel‐up position. Because we know that
horses with navicular syndrome/disease. 35,84,100,122 In one many horses with “navicular disease” commonly also
study, only approximately 50% of the horses with lame- have injuries to the supporting soft tissues, the test can
ness localized to the navicular region responded posi- also be performed in a medial and lateral up position.
tively to hoof tester pressure over the central third of the With the foot placed in the lateral wedge position, the
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frog. In contrast, a nonfatiguable painful withdrawal lateral aspect of the foot is placed in compression while
to intermittent hoof tester pressure over the central and the medial aspect of the foot is placed under tension.
occasionally the cranial third of the frog is considered a The authors have found horses with confirmed DIP joint
fairly consistent feature of navicular disease/syndrome disease and injuries to the collateral ligaments (CLs) of
by others. In addition, it is important to apply direct the DIP joint to show a positive response to this test.
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compressive pressure to the navicular region rather than
simply applying lateral (shearing pressure) across the
frog when using the hoof testers. Horses with very thick Diagnosis
soles and hard frogs usually do not respond to hoof Local Anesthesia
tester pressure. Hoof tester pain may also be present
over the toe secondary to bruising from landing toe first The diagnosis of navicular disease/syndrome begins
but is usually of minor clinical significance. with localizing the site of lameness to the foot or more
Distension of the DIP joint is a nonspecific finding specifically to the palmar aspect of the foot using diag-
that may be found in normal horses as well as horses nostic anesthesia. Historically, a PD nerve block was
with navicular disease. DIP joint distension was identi- thought to only desensitize the palmar aspect of the
35
fied in only 4.2% of horses with various injuries to the foot, but it is now known that it is relatively nonspecific
foot that were confirmed on MRI and is often detected and alleviates pain in the navicular bone, podotrochlear
84
more frequently by MRI than by clinical examination. 44,76 apparatus, navicular bursa, distal aspect of the DDFT,
However, the presence of DIP effusion may be an impor- distal phalanx, middle phalanx, DIP joint, dorsal aspect
tant finding when developing a treatment plan for an of the hoof, and possibly the digital tendon sheath and
individual horse. In addition, asymmetrical DIP joint PIP joint. 96,102 Therefore, a multitude of clinical prob-
effusion is usually clinically relevant and often suggests lems in the foot can be desensitized with a PD block; this
a secondary problem within the joint. Many horses with has been confirmed in numerous studies. 38,39,41,84,100,101
navicular disease/syndrome may react positively to a Using a small volume of anesthetic (1.0–1.5 mL) and
phalangeal flexion test, which often exacerbates the performing the PD block as low as possible in the heel
lameness. 115,135 However, a positive phalangeal flexion region (axial and distal to the proximal limits of the
test is not specific for the navicular region and is usually collateral cartilages) is recommended to improve the
not that beneficial in localizing the lameness to the foot. specificity of the block to the structures within the pal-
A positive phalangeal flexion may suggest a primary or mar aspect of the foot. 46,96,108,109,111 Several studies have