Page 533 - Adams and Stashak's Lameness in Horses, 7th Edition

Lameness of the Distal Limb 499

measurement to pre-disease baseline radiographs to accu- variety of techniques (discussed below) in an attempt to
rately assess any changes in the individual horse. Unilateral find the type of digital support that the animal responds
VetBooks.ir sopalmar/dorsoplantar projection (Figure 4.67).
to favorably.
distal displacement can only be reliably assessed on a dor-
Palmar/plantar rotation of the distal phalanx away
from the dorsal hoof wall resulting in an angle greater Anti‐inflammatory Therapy
than 5° confirms the diagnosis of laminitis due to capsu- Anti‐inflammatory therapy has endured as a central
lar rotation (normal horses can have angles less than 4°). component of laminitis pharmacotherapy over the years.
Two types of rotation can be assessed. Capsular rota- As discussed above, there is compelling evidence to use
tion, the degree of rotation between the dorsal hoof wall nonsteroidal anti‐inflammatory drugs (NSAIDs) due to
and the parietal surface of the distal phalanx (α in marked inflammatory events occurring both prior to
Figure 4.73), is best reserved for assessment in the acute and at the onset of lameness in the laminitic horse.
stage because the measurements can be difficult to inter- Therefore, aggressive, prudent use of NSAIDs is indi-
pret in horses with chronic laminitis due to deformation cated in the horse known to be at risk of laminitis (i.e.
of the hoof wall. The angle of solar margin of the distal colitis, grain overload, etc.) until approximately 48–72
phalanx to the ground surface (β in Figure 4.73) is more hours after the animal is no longer showing clinical signs
useful in horses with chronic laminitis because it will of systemic inflammation/toxemia.
remain unaffected by dorsal hoof wall deformation. In addition to blocking COX enzyme activity, high
Serial radiographs should be taken to monitor the pro- doses of NSAIDs recently have been found in other spe-
gression of the disease and determine the success of cies to block inflammatory pathways including some
selected treatments. Digital venography in the standing controlling basic inflammatory gene expression, some of
9
horse has been developed as a prognostic aid to assess which are upregulated in the early stages of laminitis.
the vasculature of the digit. A venogram in which there COX‐2 has recently been shown to be an important
is no filling of contrast of the lamellar vessels, the mediator in the synapses of sensory neurons; therefore,
circumflex area, and the terminal arch is reported to COX‐2 inhibition is likely to not only decrease lamellar
indicate an extremely poor prognosis for recovery. 63 inflammation but also decrease central pain sensation.
Due to the gastrointestinal (GI) and renal toxicity caused
Treatment by NSAIDs, close attention must be paid to the animal’s
history (i.e. a history of gastric/colon ulcers or renal dis-
The goal in the treatment of the acute laminitis case ease), the animal’s hydration status, and laboratory
is to stabilize the digit in the short term regardless of the work in the critical case to assess renal function.
degree of displacement. In the authors’ opinion, if The four main NSAIDs available to the equine clini-
the clinician can attain stabilization of the digital lamel- cian are three nonselective COX‐1/COX‐2 inhibitors
lae for approximately 3 weeks, distal phalangeal dis- (flunixin meglumine, phenylbutazone [PBZ], and keto-
placement can be addressed with other techniques profen) and one COX‐2 selective NSAID (firocoxib).
including corrective shoeing and possibly deep digital There is some question whether, during treatment with a
flexor tenotomy in nonresponsive cases. In regard to COX‐2 selective NSAID in the peracute phase of lamini-
foot support, the veterinarian must be willing to try a tis, the vascular inflammation/injury occurring in the
lamellae may place the digit at risk of the same vascular
accidents (thrombosis leading to myocardial infarction
and stroke) that have resulted with the use of COX‐2
selective drugs in humans. Thus, until proven otherwise,
it may be best to use a nonselective drug in the peracute
stage and consider firocoxib in the chronic, long‐term
case in which the drug’s decreased incidence of side
effects is more important. Meloxicam is available in
countries other than the United States and may be of
value due to slight COX‐2 selectivity (approximately
two‐ to threefold), which appears to make it a very safe
option due to a low incidence of side effects and possi-
bly fewer chances of unwanted vascular events. 10
In the horse still demonstrating signs of systemic ill-
ness with a possible ongoing bacterial toxemia (i.e. coli-
tis), flunixin meglumine is indicated due to its increased
efficacy against endotoxemia. In the animal that has a
stable hydration status and no indication of renal com-
promise or intestinal ulceration, the use of high‐dose
(1.1 mg/kg IV TID) flunixin may be indicated for up to
3–5 days; the authors decrease the dosage after 3 days if
Figure 4.73. For assessment of rotation of the distal phalanx,
the clinician can assess the degree of capsular rotation (angle α) at the source of bacterial toxemia appears to be resolving.
the intersection of the dorsal capsular and dorsal phalangeal lines If the lameness does not improve with flunixin, it is indi-
or can measure the difference between the dorsal angles δ and ε. cated to either add other types of analgesics (see con-
The relationship of the solar margin of the distal phalanx to the stant rate infusion [CRI] below) or possibly lower the
ground surface of the foot can be assessed by measuring angle β. flunixin dosage by half and add 4.4 mg/kg PBZ SID.