Page 691 - Adams and Stashak's Lameness in Horses, 7th Edition

Lameness of the Proximal Limb 657

THE TARSUS

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INTRODUCTION tarsus should begin with a thorough radiographic and
sonographic examination. The complicated anatomy of
The forelimb receives 60%–65% of the weight of the this joint can significantly compromise a complete exam-
horse and rider during locomotion, while the hindlimbs ination with these two imaging tools, 59,60,77 and the use of
are used primarily to generate forward momentum. nuclear scintigraphy, CT, or MRI may be required to find
Performance horses (other than racehorses) require a the source of pain. Currently MRI is considered the gold
rearward shift in weight distribution, which allows more standard for imaging the distal limbs of the horse but is
impulsion from the hind end. In particular, the disci- not without risk to the horse because it requires general
plines of dressage, eventing, and show jumping are good anesthesia. Because of the complexity of the tarsus, the
examples of horses that need to work “off the forehand” examiner must develop a keen understanding of the nor-
and drive through the hind end during collection and mal anatomy and the types of injuries that typically can
propulsion. This change in weight distribution increases occur in the tarsal region to most effectively utilize diag-
the incidence of hindlimb injuries seen in sport horses. nostic analgesia and imaging techniques.
The tarsus accounts for many of the hindlimb lameness
conditions in performance horses, and the appropriate
use of diagnostic imaging is critical to accurately diag-
nose the specific site of the problem. DIAGNOSIS OF TARSAL LAMENESS
Horses with hindlimb lameness may demonstrate lit- Exam and Palpation
tle evidence of the source of lameness. In addition, it
may prove difficult to examine the hindlimb due to the An accurate diagnosis is critical to effectively manage
potential risk of injury, be it real or perceived. Many injuries of the tarsus. The diagnosis of tarsal disorders of
equine professionals (owners, trainers, and veterinari- the hindlimb can be challenging. Often clinical signs are
ans) rightly or wrongly suspect the tarsus or stifle to be not obvious or specific to the tarsus, and lameness is
the most common source of lameness. However, the thought to originate from more proximal on the limb.
gait characteristics of hindlimb lameness are similar Careful examination of the distal limb can provide some
irrespective of whether the source of pain occurs in the indication of a specific problem that coexists with tarsal
proximal or distal limb. A careful and consistent clini- problems. Structures in the distal limb and tarsus should
cal examination and the use of diagnostic analgesia can be palpated with the horse standing on the limb and
identify the most likely region that may be the cause with the limb raised. Application of hoof testers should
of the lameness. Radiographic and ultrasonographic be performed in acute cases to rule out the presence of
examinations are complementary and quite effective pain associated with the foot before evaluating the rest
tools in the evaluation of both bone and soft tissue of the limb. Some injuries may involve multiple struc-
structures of the limb of the horse. 20,23,32,35,36,58,63,106,116,140,144,146 tures, so it is critical to develop a complete routine
When these techniques are unable to define a specific examination protocol of the entire limb. Manipulation
cause of lameness, then more advanced diagnostic tech- of the limb by flexion, extension, and rotation may pro-
niques such as nuclear scintigraphy, computed tomog- vide some indication of joint(s) involvement. Flexion
raphy (CT), or magnetic resonance imaging (MRI) may tests to accentuate lameness may be helpful to differenti-
be required. 7,13,14,21,44,45,49,59,102,103,109,115,119,125,137 An accu- ate lower limb from the proximal limb involvement.
rate diagnosis and prognosis becomes critical to effec- However, the reciprocal apparatus of the hindlimb
tively address and rehabilitate injuries in these cases of makes it virtually impossible to flex the lower limb and
lameness. proximal limb separately. The degree of flexion of the
Strain‐induced injury of both the soft tissues (tendons distal limb, however, can be exaggerated beyond that of
and ligaments) and bone (modeling) are the most com- the proximal limb by holding the leg as close to the
mon causes of orthopedic injury in athletic animals, ground as possible (similar to how the farrier holds the
either equine or human. Injuries of the structures of the limb) and selectively flexing the lower limb. Performing
tarsus are quite common and are diagnosed with a com- the distal limb flexion first before the proximal limb
bination of clinical examination, diagnostic analgesia, allows a comparison between the respective outcomes.
and diagnostic imaging. 7,17,24,40,43,54–57 While clinical Many horses with proximal limb involvement may
examination can often suggest the region of the tarsus as respond markedly to both distal and proximal limb flex-
a clinical problem, intra‐articular and/or regional anes- ion. In general, flexion tests of the hindlimb have low
thesia should be utilized to confirm and to more accu- specificity, which should emphasize the use of diagnostic
rately isolate the source of lameness. If the lameness has analgesia to confirm the source of lameness.
been isolated to as specific an area of the tarsus as pos-
sible, then diagnostic imaging should be focused on this
area. Once an accurate diagnosis is attained, the clinician Diagnostic Analgesia
can develop a directed treatment strategy and rehabilita- Diagnostic analgesia should be utilized to isolate
tion schedule for that specific problem(s). Imaging of the the source of lameness either by sequential regional