Page 605 - Adams and Stashak's Lameness in Horses, 7th Edition

Lameness of the Distal Limb 571

Postoperative exercise should be limited for at least 3 FRACTURES OF THE THIRD METACARPAL/
months. Stall rest confinement is recommended for this METATARSAL (CANNON) BONE
VetBooks.ir begin. Follow‐up radiographs should be taken 3 months non) bone occur commonly in all ages, but more com-
period, and after 2 months hand‐walking exercise can
Fractures of the third metacarpal/metatarsal (can-
postoperatively, and if the healing is progressing nor-
mally, the horse can be turned out into a small paddock monly in young horses, and all breeds of horses. The
for an additional month. The training schedule depends metacarpus/metatarsus is particularly susceptible to
on the type of fracture but could begin as early as 4 fracture because of the distal location and because little
months or as late as 6 months. In one study horses were soft tissue covers the bone to help absorb impact energy
more likely to race if the fracture line could no longer be in blunt trauma. 120
identified at the 2‐ to 4‐month radiographs. 146 Although fractures of the cannon bone can assume a
Screws are generally not removed after healing has variety of configurations, ranging from a simple fissure
occurred unless residual lameness results that can be to severe comminution, younger horses seem to sustain
directly attributed to their presence. In a review of 233 simpler fractures than adults, possibly because of more
cases of condylar fractures, most repaired by interfrag- elastic and less brittle and shatter‐prone bone. Frequently,
mentary compression, screws were only removed in 20 distal fractures that involve the growth plate, or rarely
of the cases, and there appeared to be no consistent dif- persistent proximal physes, in young animals are Salter
79
ference in the performance between this group and the type II fractures (Figure 10.7). Because of the minimal
group with screws in place. This study noted that horses soft tissue covering, the fractures are commonly open or
8
with screws placed closer to the joint had a lower return become open soon after the injury occurs. More than
to racing. Subchondral sclerosis was proposed as a cause half of referred metacarpal/metatarsal fractures are
84
for this pain. In general, removal of screws is not rou- open. Concurrent fractures of the small metacarpal
tinely performed for condylar fractures except if screws bones are common. Stress fractures of the metacarpus
are placed in the diaphysis such as in medial condylar and metatarsus in racehorses that can progress to acute
fractures of the metatarsus or spiraling fractures. Screw and complete failure of the bone are discussed earlier in
removal is easily performed under general anesthesia; this chapter. Once catastrophic failure occurs, fractures
the location of the screws can be confirmed with marker are treated as discussed below.
needles and radiographs. In most cases the screws can be
removed through small stab incisions alone. Bone plates Etiology
are always removed in horses intended for athletic pur-
suits following surgery. Standing plate removal can usu- External trauma in any form can cause fracture of the
ally be performed 3 months following surgery, provided cannon bone, e.g. kicks and falls. When foals are
the fracture has healed well. Stall rest for an additional affected, the dam has often stepped on the limb, causing
30 days is required after plate or screw removal, fol- a fracture. Propagation of stress fractures or propaga-
lowed by stall rest with hand walking for an additional tion of forces through screw or transfixation pin holes
30 days. can result in similar complete cannon bone failure.

Prognosis Clinical Signs and Diagnosis
The general prognosis for athletic performance and Complete yet nondisplaced fractures of the cannon
returning to racing is excellent for nondisplaced incom- bone secondary to direct trauma can occur and may be
plete fractures, whether treated conservatively (82% difficult to initially diagnose (Figure 4.147). The lame-
and 87% in two reports) 8,146 or following internal fixa- ness may be nonspecific and variable. Heat, swelling of
tion (74% and 79% in two reports) for forelimb frac- the soft tissues overlying the fracture, and pain on deep
tures, 8,146 and 93% for metatarsal fractures in one digital palpation are usually present. A wound at the site
8
report. Prognosis for athletic performance and return of impact is also often present. Diagnosis may be delayed
to racing is fair for complete displaced and nondis- if soft tissue injury is evident because the lameness may
placed fractures following internal fixation (58% in be attributed to this cause. As lameness persists or wors-
one report). In two other reports, 33% of complete ens, radiographs are often taken and may reveal fracture
146
fractures (displaced and nondisplaced) and 19% of lines. If the horse is turned out, invariably complete
8
displaced fractures returned to racing. Rapid immo- bone failure occurs. If stall confinement is maintained,
45
bilization and repair of displaced fractures probably the diagnosis is often made at the second radiograph
can dramatically affect outcome. In cases of complete when periosteal reaction is noted at sites of cortical exit
displaced fractures or when there has been a delay in and bone resorption of the fracture line widens the
diagnosis and treatment and/or improper immobiliza- fractures.
tion has been selected, a guarded to poor prognosis can In complete bone failure, the diagnosis of fracture of
be expected. Only 12 of 38 cases in one report were the cannon bone is obvious (Figure 4.148). In all cases,
112
112
able to return to racing. This prognosis is altered these fractures should be immediately supported and
because of increased damage to the articular surface then radiographed to identify the type (simple vs. com-
that is likely to result in OA of the fetlock. The progno- minuted) and location in relation to joint surfaces. The
sis for return to racing is considered poor for commi- limb should not be manipulated excessively during the
nuted fractures or subchondral bone lesions in the physical exam because this may lead to penetration of
palmar or plantar surface of the distal end of the can- bone fragments through the skin. If treatment is to be
non bone. 112 considered or further diagnosis is to be obtained, a cast