Page 529 - Adams and Stashak's Lameness in Horses, 7th Edition

Lameness of the Distal Limb 495

four limbs affected. Whereas, with only forelimb involve-
ment, the animal places its forelimbs and hindlimbs far-
VetBooks.ir place more weight on hindlimbs), the animal with involve-
ther forward than normal (to get weight off forelimbs and
ment of all four limbs may place the forelimbs forward
and the hindlimbs further caudad than normal (appear-
ing “camped out”).
The equid at risk of endocrinopathic laminitis is now
realized to not always be as straightforward to identify
as those at risk of the other types of laminitis. The two
primary types of endocrinopathies putting the horse at
risk of endocrinopathic laminitis, EMS and PPID, can
have disparate presentations. For EMS, similar to the
human component of metabolic syndrome, obesity is a
major risk factor. Additionally, and also in parallel with
findings in human medicine, genetics are recently being
Figure 4.69. A sagittal section of the hoof wall of a horse with ascribed a larger role in EMS. This interplay between
capsular rotation of the distal phalanx. Note the lamellar wedge obesity and genetics is most clearly demonstrated by
(black arrows) of epithelial tissue that forms from remaining lamellar overweight animals that never exhibit signs of EMS‐
epithelial cells following displacement of the distal phalanx. Also associated laminitis (EMSAL). Conversely, there are
note the penetration of the sole by the dorsodistal tip of the distal cases of athletic animals with only a moderately elevated
phalanx immediately dorsal to the apex of the frog (white arrow).
body condition score (e.g. show jumpers) that develop
EMSAL. Similar to EMS, it has recently been reported
reasons: they do not accurately describe the range of clini- that not all animals diagnosed with PPID are at risk of
cal cases (not all patients with sepsis are actually in the laminitis, only those with insulin dysregulation. Thus,
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developmental stage of SRL), and, furthermore, they do diagnostic testing needs to be combined with physical
not lend themselves to treatment recommendations. signs to establish those animals at risk of endocrino-
Rather than these categorizations, it is best to describe the pathic laminitis. Animals with pasture‐associated lami-
initial period as an “at‐risk” period instead of a prodro- nitis (animals that develop laminitis when exposed to
mal or developmental period. In addition to defining the lush pasture) are included in EMSAL; these animals may
animal at risk for the different types of laminitis (for pro- exhibit the classic signs of laminitis (i.e. digital pulses,
phylactic management of the animal), it may be best to hoof warmth) after a short period of time on pasture or
define the acute and chronic stages in a temporal sense, may undergo an insidious displacement of the distal
with the acute stage being the first 3–4 weeks after signs phalanx that may go unnoticed for extended periods of
of laminitis first occur (regardless of the placement of the time. These animals may exhibit no clinical signs of foot
distal phalanx) and the chronic stage being the animal pathology while a gradual displacement of the distal
treated from 4 weeks to years later. phalanx is occurring (likely over months to years). Thus,
The equid at risk of SRL is an animal suffering from an in the authors’ experience, the first sign of foot disease
infection (e.g. enterocolitis, pneumonia, acute endometri- detected by the owner or trainer may be lameness from
tis) or from a compromised viscus (e.g. volvulus of the solar bruising due to the pressure of a moderately to
large colon) that results in the animal exhibiting systemic severely displaced distal phalanx on the solar tissue. For
signs of sepsis/endotoxemia (e.g. fever, injected mucous this reason, it has been suggested to obtain radiographic
membranes, tachycardia). Although SRL research has films of the forelimb digits once a year to detect any
demonstrated that lamellar inflammatory events begin changes in the relationship of the distal phalanx to the
long before the animal exhibits clinical signs of lamini- hoof wall (see chapter on imaging component).
tis, 28,47 it has also been documented in both the clinical The equid at risk of SLL is the animal preferentially
and research setting that effective intervention with digi- bearing weight on one limb due to injury/disease to the
tal hypothermia (discussed later) even early into the onset contralateral limb causing pain or inability to place
of clinical lameness can protect the lamellae from struc- weight on that limb. This can occur due to fracture, syn-
tural failure. 18,25 Thus, it is critical to detect these animals ovial sepsis, nerve injury leading to paresis, or even long‐
at risk of SRL for initiation of prophylactic therapy. Most term subsolar sepsis. Although SLL usually occurs in the
animals with SRL will exhibit signs of laminitis prior animal with severe unilateral lameness, it can occur in
to lamellar failure/displacement of the distal phalanx, the animal with moderate lameness. In a survey of
including throbbing digital pulses, increased hoof warmth, equine surgeons in private and university practices, they
response to hoof testers, and lameness especially exacer- reported that the most common cause of lameness in the
bated on tight turns. Again, in the authors’ experience, contralateral limb in SLL cases was sepsis of synovial
this is likely the last possible time point to initiate therapy structures. Similar to endocrinopathic cases, there is
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to avoid lamellar failure, as, once the animals are exhibit- not a defined developmental period, as SLL may develop
ing severe lameness (i.e. Obel grade 3–4 laminitis), severe any time from 2 to 3 days to over 60 days of preferential
lamellar injury and displacement of the distal phalanx are weight‐bearing on one limb. The animal at risk of SLL
commonly already present. In the interest of identifying may exhibit signs of the disease within a few days of
patients early in the disease process, it is important to becoming lame on the opposite limb, although signs of
understand that although the forelimbs are usually most laminitis commonly occur after the animal has
severely affected in SRL, it is also the subcategory of lami- been exhibiting lameness on the opposite limb for
nitis in which patients stand the greatest risk of having all several weeks. Once signs of laminitis occur, the SLL is