Page 589 - Adams and Stashak's Lameness in Horses, 7th Edition

Lameness of the Distal Limb 555

matic rupture of the DSLs. Transverse or comminuted injuries to the suspensory apparatus were more likely in
fractures of both proximal sesamoid bones allow the males, older horses, and horses in training without any
VetBooks.ir the SL while the basilar fragments remain attached to cumulative high‐speed exercise. 69
starts, and there was no association between injury and
apical portions to be drawn proximally by the pull of
the DSLs. Occasionally, open luxation of the fetlock
joint can occur. Besides the severe trauma sustained by Clinical Signs
the supporting soft tissues and bone, the adjacent digital
arteries are frequently damaged sufficiently to result in On gross observation the affected fetlock is usually
ischemic necrosis of the hoof. Treatment of traumatic very swollen, and the horse usually bears its entire
rupture of suspensory apparatus should only be consid- weight on the unaffected limb. The lameness is obvious,
ered as a salvage procedure. and if the animal transfers its weight to the affected
limb, the fetlock will sink to the ground. Palpation often
Etiology reveals the proximal displacement of either the intact
sesamoid bone or the apical fractured fragments.
Extreme overextension of the fetlock is the likely cause Immediate stabilization of the limb is critical to prevent
for disruption of the suspensory apparatus. Preexisting rupture of the neurovascular bundles. The blood supply
pathology of the bones or SL need not be present for this to the distal limb can be estimated by palpation of a
catastrophic failure to occur, but the presence of an pulse, presence of distal bleeding and/or use of Doppler
abnormal finding in the SL on prerace inspection by a devices, or the IV injection of 5 g of sodium fluorescein.
90
regulatory veterinarian increased the risk of SL injury The vascular supply is best evaluated after the horse has
3.4‐fold in future races as compared with a control popu- been treated for shock and the limb stabilized. Intense
23
lation. In a recent postmortem study of Thoroughbred vasoconstriction initially can be interpreted as lack of
racehorses, moderate lesions identified in the SL branches blood supply.
or DSLs were more likely to occur in horses that died
from suspensory apparatus failure or metacarpal condy- Diagnosis
lar fractures than in horses that died from nonmusculo-
skeletal causes. Factors that increase the strain on the Radiographic examination usually reveals either the
40
flexor surface of the limb would be expected to increase proximal displacement of the intact sesamoid bone or
the risk of suspensory apparatus failure. Thoroughbred proximal displacement of the apical portions of the frac-
horses racing with low toe grabs or full toe grabs were 6.5 tured sesamoid bones (Figure 4.136A). Associated swell-
and 15.6 times more likely to incur a fatal suspensory ing of the soft tissues is also quite evident, and preexisting
apparatus injury than horses without toe grabs. A study degenerative lesions within the sesamoid bones and fet-
48
of Thoroughbred horses in New Zealand suggested that lock joint may also be present. 100

A B
Figure 4.136. (A) Rupture of the distal sesamoidean ligaments causing proximal displacement of the proximal sesamoid bones.
(B) Postoperative appearance of the same horse in (A) after fetlock arthrodesis.