Page 641 - Adams and Stashak's Lameness in Horses, 7th Edition

Lameness of the Proximal Limb 607

Occasionally a fistula can be seen during arthroscopic
surgery, but closure of the fistula requires an arthrot-
VetBooks.ir problem, without repair of the fistula, has resulted in
omy. Arthroscopic surgery for treatment of a primary
resolution of lameness without resolution of the swell-
ing. Fistulae are typically not repaired unless a cosmetic
effect is important, if the swelling itself is impeding
performance, or if medical therapy fails to alleviate
lameness.

INTRA‐ARTICULAR FRACTURES

Although most horses with intra‐articular fracture of
the carpus display acute onset of clinical signs, the dam-
age is chronic in nature, at least in racehorses, and occurs
at consistent sites in the dorsal aspect of the joints. The
damage is the end result of a chronic process in which
stress‐related subchondral bone damage occurs. 59,111
The pathogenesis of repetitive stress injury is discussed
in Chapter 7. Acute fracture and fragmentation of the
carpus can occur, but this is typically in unusual loca-
tions, especially in the palmar aspect of the joints, mak-
ing an accurate prognosis difficult to make. Therefore,
in equine athletes, and particularly racehorses, the dam-
age occurs in predictable sites that lend themselves to
more accurate prognosis with treatment. Figure 5.10. Oblique radiograph of the carpus demonstrating
Three types of fractures can occur within the carpal osteochondral fragmentation of the proximal third carpal bone
joints of the horse: osteochondral fragmentation, slab (white arrow). Although this site of damage is seen more commonly
fracture, and comminuted fracture. in Standardbreds, this was a racing Quarter horse. Source:
Osteochondral fragmentation occurs on a single Courtesy of Dr. Gary Baxter.
articular surface and is commonly found on the radial
carpal, third carpal, intermediate carpal bone, and distal surfaces), and although they are most common in the
radius. The fragments can be attached with fibrous tis- third carpal bone, they can occur in the intermediate
sue, loose, or free within the joint and are categorized as and radial carpal bones as well. In Thoroughbreds and
(1) recent and complete fragment; (2) fragment with Standardbreds, slab fractures commonly occur on the
capsule attachment; (3) chronic fragment with bone third carpal bone and primarily affect the radial facet.
attachment, usually by fibrous tissue; or (4) fragment These fractures can also occur on the intermediate facet,
with extensive attachment to the bone. 13 both facets, or in a sagittal orientation. 75,105,116
Regardless of the type of fragmentation, osteochon- Comminuted fractures of the carpus occasionally
dral fragmentation typically occurs at consistent loca- occur, and although they primarily involve the third
tions; again, this reflects the chronic nature of the carpal bone, they can also involve the radial carpal,
disease. Thoroughbreds and Quarter horses commonly intermediate carpal, and fourth carpal bones. Horses
show fragments within the radiocarpal and middle car- that suffer these fractures are usually axially unstable.
pal joints. In Thoroughbreds, fragmentation commonly They require emergency stabilization and usually
occurs off the distal aspect of the radiocarpal bone, surgery to be sound for breeding.
distal lateral radius, and proximal aspect of the interme- In addition to fragmentation and fracture of the car-
diate carpal bone. In Japan, the most common sites for pus, it is not unusual to find subchondral bone lysis that
fragments to occur in Thoroughbred racehorses are the leads to pain, typically in racehorses. This primarily
distal lateral radius, proximal aspect of the third carpal occurs in older Standardbred racehorses due to chronic
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103
bone, and distal aspect of the radiocarpal bone. In rac- stress‐induced disease within the subchondral bone.
ing Quarter horses, fragmentation occurs off the distal This syndrome is discussed in the OA section of this
aspect of the radiocarpal bone, proximal aspect of the chapter.
intermediate carpal bone, and distal lateral radius. In
79
Standardbreds, the fragmentation typically occurs in the Etiology
middle carpal joint, especially on the third carpal bone
(Figure 5.10). 69,93,105 It is important not to rely on these The biomechanical forces that occur in the carpus
generalizations because fragmentation can occur any- and lead to fracture are difficult to characterize due to
where within the carpi and the distribution may differ the large number of bones and soft tissues involved. The
with different population bases. Fragmentation can carpal bones are not in direct contact with their oppos-
81
also occur at the palmar aspect of the antebrachial ing surfaces during the flight phase of the gait. However,
carpal and middle carpal joints. 62,127 with weight‐bearing and full extension, it is hypothe-
Slab fractures of the carpus usually occur completely sized that the carpal bones assume a congruent articula-
through the bone (they fracture through both articular tion with their opposing bones. It is also hypothesized
3,5