Page 669 - Adams and Stashak's Lameness in Horses, 7th Edition

Lameness of the Proximal Limb 635

caudad and the proximal fragment being displaced In an in vitro model, the configuration of the fracture
craniad). However, it is uncommon for proximal com- was predictable and depended on the direction from
VetBooks.ir the stability provided by the surrounding muscles in a craniocaudal direction, the humerus fractured trans-
which the insult originated. When the force was applied
plete humeral fractures to become displaced because of
versally; when the force was applied in lateral to medial
(supraspinatus, infraspinatus, subscapularis, and del-
toid), biceps tendinous insertions, and periarticular cap- direction, the humerus fractured obliquely. 56
sular attachments of the shoulder. Incomplete stress Horses sustaining stress fractures are at an increased
66
fractures occur in two typical locations: the proximal risk to develop a complete fracture if they are not
caudal lateral cortex and the distal cranial medial managed properly. A study of 34 Thoroughbred race-
cortex. 56 horses with humeral stress fractures found an increased
The radial nerve courses in the musculospiral groove risk of complete fracture in horses that returned to
13
of the humerus and may be traumatized to varying racing after a short 2‐month lay‐up period. In one
degrees as a result of complete displaced diaphyseal or study that did not have any horses develop complete
metaphyseal humeral fractures. 11,55 The damage may fractures during rehabilitation, the mean time to
range from a minor neuropraxia to a complete sever- return to racing for horses with humeral fractures was
67
ance of the nerve. Because of the profound effect on 7.5 months. Radiographic and scintigraphic reex-
prognosis, it is important to evaluate the degree of nerve amination allows for more accurate assessment of
dysfunction early in the convalescent period. recovery. 85

Etiology Clinical Signs
Humeral fractures frequently occur in foals, in wean- Horses with nondisplaced or minimally displaced
lings secondary to falls or other impact injuries, and in proximal fractures (Salter–Harris type I epiphyseal,
racing breeds as either catastrophic failure during race greater tubercle, or deltoid tuberosity) and nondisplaced
falls or failure as a result of accumulated stress and midshaft fractures often present with a history of a
microfracture. 11,56,60,96 In a study of 54 horses with severe lameness that improves over a 24‐ to 48‐hour
humeral fractures, falls on hard surfaces or related to period. Moderate swelling may be present at the site of
racing were responsible for fractures in 11 horses, kicks injury for a proximal fracture or over the lateral muscles
in 2 horses, post‐anesthetic recovery in 2 horses, colli- for a midshaft fracture or even distal if a few days have
sions with fences or another horse in 3 horses, and car passed. Pain is often present with pressure applied over
collision in 1 horse. Trauma is the cause of most frac- the fracture and on limb manipulation. Radiography
14
tures of the deltoid tuberosity or greater tubercle. 60 often provides a definitive diagnosis.
Incomplete fractures and stress fractures resulting in
lameness can be most difficult to diagnose. 52,56,67,80,91 In
some cases lameness and mild swelling may be adequate
to lead to a tentative diagnosis of a fracture, but the
definitive diagnosis often requires nuclear imaging. 67
Horses with complete displaced fractures often pre-
sent with a history of an acute onset of a severe non‐
weight‐bearing lameness. Marked to moderate swelling
of the muscles overlying the region is often seen, and the
elbow is usually dropped (Figure 5.43). The dropped
elbow may be due to the overriding of the fracture seg-
ments resulting in functional limb shortening or from
the varying degrees of damage to the radial nerve.
14
Limb manipulation usually causes increased pain and an
increased range of motion when the limb is adducted
and abducted. Crepitation is often difficult to appreciate
in heavily muscled horses, with the muffling effect of the
swollen musculature. Limited manipulation should be
done because it may result in further trauma to the
radial nerve. Radiographs will identify the fracture, but
evaluation of radial nerve damage is more difficult.
Electromyography (EMG) of the antebrachial extensor
muscles can be used after 2 weeks to evaluate radial
nerve damage. In one study 4 of 40 horses treated for
fractures of the humerus were destroyed because of loss
of radial nerve function. 14
Fractures of the distal epiphysis, condyles, and epi-
condylar region are very uncommon. 26,62,89 When they
Figure 5.43. Radial nerve paralysis, evidenced by the classic do occur, they often present with a history of marked
dropped elbow stance. This stance can also be seen in horses with lameness of a short duration. Swelling associated with
ulna and humeral fractures, but accompanying soft tissue swelling is the elbow region may be apparent, including joint
usually present. Source: Courtesy of Dr. Gary Baxter. effusion if the fracture is articular.