Page 602 - Adams and Stashak's Lameness in Horses, 7th Edition

568 Chapter 4

of Standardbreds (6 of 7 treated surgically) raced after In a histopathologic study on North American race-
treatment. In summary, return to racing in Thoroughbreds horses, similar palmar condylar cartilage fibrillation
VetBooks.ir limb fractures, evidence of sesamoid fracture, or female sis were noted. Evidence of active bone remodeling was
with underlying bone sclerosis and areas of bone necro-
was significantly reduced with complete fractures, fore-
present around the sclerotic zones with osteocyte necro-
sex (presumed retired for breeding). Complete condylar
8
fractures tend to be longer (mean 85 mm) than incom- sis apparent as prominence of subchondral vessels and
plete fractures (mean 57 mm). Axial sesamoid fractures osteoclastic activity. Fragmentation lines indicating
112
are associated with displaced lateral condylar fractures matrix fragility and microfractures were apparent. This
that disrupt the collateral ligament and avulse the inters- area of the condyle was grossly flattened. Similar
92
esamoidean ligament complex. 6 microdamage including microfractures in regions of
Another report of 124 condylar fractures in osteoporosis and thinning of the zone of calcified carti-
Thoroughbreds corroborates the above findings of the lage was seen histologically in the bone of lateral condy-
more recent reports. It was noted that 90% of condylar lar fractures obtained from fatal injuries. In an
134
fractures occurred in 2‐ and 3‐year‐olds and that most experimental study with controlled training exercise,
were acquired during training between April and bone density, particularly in this palmar condyle region,
October. In this report, 17% of displaced lateral condy- was significantly greater in horses with high intensity
lar fractures returned to racing. The variation in exercise. In summary, the palmar condyle is the site of
113
45
successful return to racing of displaced condylar frac- maximum loading in racing, and the bone responds by
tures may be related to the duration of fracture prior to increasing density (sclerosis). Bone fatigue failure occurs
surgery. Destruction of the articular surface occurs and, due to the normal columnar arrangement of the
quickly following a displaced fracture; therefore, imme- bone trabeculae, propagates acute failure in the configu-
diate immobilization and repair are critical to a success- ration seen in condylar fractures (Figure 4.145).
ful outcome. 111
Condylar fractures of the hindlimb are more com-
mon in Standardbreds and are more likely to be medial Clinical Signs
and to not exit the cortex. These fractures can propagate The clinical signs may vary from a mild lameness that
proximally or progress to a complete “Y” fracture, even is exacerbated by exercise with little heat or swelling
with stall confinement. 110,111 present with nondisplaced, incomplete fractures to
severe lameness with heat, pain, and swelling in the
Etiology acute, displaced fracture. The incomplete, nondisplaced
fractures are often so subtle that they are missed on
The etiology includes trauma from high compressive physical examination, but may be detected by radio-
loads, asynchronous longitudinal rotation of the cannon graphs, nuclear scintigraphy, or CT. However, fetlock
bone, and exercise on uneven surfaces. The risk of fatal joint effusion is usually present because fractures origi-
condylar fracture in Thoroughbred racehorses is 7 times nate at the articular surface. This is best seen in the
and 17 times more likely if horses are shod with low or palmar or plantar recess of the fetlock joint capsule. The
regular toe grabs, respectively. The toe grab changes external swelling of the lateral side of the large metacar-
66
the hoof angle and presumably places more stress on the pal or metatarsal bone depends on the degree of separa-
suspensory apparatus and plants the foot more securely. tion of the proximal end of the fragment and is readily
This likely alters the compressive and rotatory forces on palpated in displaced fractures. More swelling is
the distal metacarpus. observed with greater separation of the fracture frag-
Recent structural studies of the distal condyle of ment. The degree of pain associated with the palpation
unexercised and exercised horses have demonstrated and the amount of heat that is felt depends on the acute-
that the normal mineralized articular cartilage tends to ness of the fracture. Fracture movement and crepitation
cleave in the sagittal plane and that the main subchon- also may be detected.
dral bone trabeculae are arranged in columns and run in Increased lameness can be observed in a horse after it
the sagittal direction with fewer mediolateral connec- has been exercised and when the horse is circled to the
tions. Blood vessel canals lie inside these sagittally affected side. Flexion and rotation of the fetlock usually
oriented structures. The sagittal column orientation pro- result in sufficient pain to cause withdrawal of the limb.
vides maximum strength and protection in the sagittal In the acute, displaced fracture, crepitation may be felt
plane in which the joint rotates but offers minimal with rotation of the fetlock. Increased lameness can be
resistance to fracture propagation in this plane. The ana- observed when flexion tests are used in cases in which
tomical course of condylar fractures of the third meta- there is a fissure fracture. Preferably, if a fracture is sus-
carpal bone can be explained by the anisotropic pected based on history, clinical signs, and joint effusion,
structural arrangement of the mineralized tissues. In radiographs should be immediately taken without fur-
18
horses in race training, densification (sclerosis) of ther lameness examination or joint manipulations to
the subchondral bone of the palmar/plantar surface of decrease the risk of propagating the fracture or worsen-
the condyles was identified by CT techniques, and this ing the articular cartilage injury.
114
correlated with linear defects in the mineralized carti-
lage and subchondral bone in the same region with Diagnosis
intense surrounding bone remodeling. Microcracks in
115
the subchondral bone of the metacarpus may coalesce It is advisable to take radiographs if a condylar frac-
and represent a preexisting pathology in horses with ture is suspected. Perineural and intrasynovial anesthe-
catastrophic fracture. 87,97 sia should be considered only after it is confirmed that a