Page 1002 - Adams and Stashak's Lameness in Horses, 7th Edition

968 Chapter 9

exacerbated by both fetlock and carpal flexion. In the
hindlimb, swelling from PSD is minimal, and horses can
VetBooks.ir ing the Churchill test, making diagnostic anesthesia crit­
be positive to any or all hindlimb manipulations, includ­
ical. In all cases, diagnosis is confirmed with ultrasound,
but radiographs should also be obtained to look for
bone abnormalities at the ligament’s origin, proximal
sesamoid bones, and the splint bones, which are fre­
quent in racing Standardbreds.
Suspensory branch desmitis is common in the
Standardbred, and it is frequently seen in horses that
train on tracks with tight turns or excessive banking.
Single branch disease is related to hoof imbalance or
poor conformation, whereas biaxial injury results from
hyperextension of the fetlock joint. Lameness is not a
prominent feature, and many Standardbreds continue to
race and train, accumulating damage and propagating
injury toward the suspensory body. Injury is easily rec­
ognized by the visible swelling at the back of the fetlock
and palpation of the enlarged branch(es).

Carpus
Carpal pain represents a significant cause of lameness
in the Standardbred. One study revealed its presence in
one‐third of the population and found it to be the top
reason for horses to require a layoff longer than 1
17
month. Lameness results in a distinctive gait character­
ized by abduction of the limb and a shortened cranial
Figure 9.18. This radiograph of the metacarpus was obtained phase of the stride from a reluctance to flex the carpus.
using the position described in Figure 9.17. This view is useful to Affected horses often stand in the stall with the knee(s)
demonstrate small fissures or sclerosis of the palmar aspect of the slightly flexed to reduce tension on the dorsal joint cap­
condyle, neither of which are present in this case. sule. Heat and swelling are invariably present and often
recognized by trainers.
Metacarpus/Metatarsus Synovitis and capsulitis are frequently encountered in
the young Standardbred. Sensitivity to palpation, pain
Standardbreds are not prone to the bucked shin com­ on flexion, and reduced range of motion are typical.
plex seen in other racing breeds, although the problem is Treatment is aimed at returning the joint to normal as
occasionally seen in forelimbs of 2‐year‐old pacers dur­ quickly as possible; NSAIDs and ice are helpful in the
ing late summer. Bruising of the hind shins may occur in acute stage. Walking should follow to regain joint mobil­
trotters that interfere, with the front foot hitting the dor­ ity and limit fibrosis. In some cases, intra‐articular hya­
sal surface of the metatarsus. luronan (HA) or steroids are needed to control the
Injury to soft tissue structures in this region is com­ inflammatory process. Suppression of synovitis is impor­
mon. The majority of cases result from repetitive stress tant to prevent the products of inflammation from com­
injury, although acute trauma and even tendon rupture promising the articular cartilage and causing arthritis.
can be seen in Standardbreds that race without adequate Osteochondral fractures in the carpus are a direct
leg protection. Tendon injuries are relatively easy to result of race training. In the Standardbred, fragments
diagnose in the Standardbred; swelling and pain prompt are mainly seen in the middle carpal joint and are almost
ultrasonographic evaluation. Injury to the superficial exclusively located dorsomedially, coming from either
digital flexor tendon (SDFT) is most common, and the the distal radial carpal bone or the proximal third carpal
severity dictates the course of treatment. Prognosis for bone. Sudden onset of carpal swelling with lameness is
14
SDFT injury appears better in the Standardbred than typical. Flexion exacerbates the lameness, and digital
other racing breeds. Horses with injury within the ten­ pressure along the dorsal aspect of each bone while the
don sheath often develop constriction by the palmar joint is flexed may help localize the source of pain. A
annular ligament and may require transection of this complete radiographic study of the carpus should be
ligament prior to racing. performed to document any chips as well as subchon­
Proximal palmar metacarpal pain is regularly encoun­ dral sclerosis. Remodeling occurs in both limbs simulta­
tered in the Standardbred, and differentials must include neously; therefore, the contralateral carpus should also
proximal suspensory desmitis (PSD), injury to the infe­ be radiographed to look for concurrent disease. In the
rior check ligament, and sagittal fracture of the cannon racehorse, most chips are clinically important, and
bone, with PSD being most likely. Horses with PSD usu­ arthroscopic removal is the treatment of choice.
ally have a head nod that is pronounced when the limb The third carpal bone is prone to maladaptive stress
is on the outside of a circle. Affected horses can move in remodeling that causes pain and fractures. Evaluation of
a manner that mimics carpal pain, and lameness may be Standardbreds in training revealed middle carpal joint