Page 96 - Veterinary diagnostic imaging birds exotic pets wildlife

92 SECTION I III The Birds

from a sudden collision with a motor vehicle, window, shaft flares laterally and medially, rounds up, and

or power line can be likened to the snapping of a wing forms the lateral and medial humeral condyles, thus
strut in a small aircraft after a fl ip on the tarmac. giving rise to the proximal aspect of the cubital or
elbow joint.
Scapula. Like the humeral head, the scapula is rarely Proximal humeral body fractures usually occur just
injured, but when it does fracture, it is usually in con- below the pectoral crest and have a strong tendency to
junction with the shoulder joint and in this respect override, often quite badly, The consequences of over-

constitutes a potential fl ight-ending injury. ride are twofold: first, the wing becomes shortened,
sometimes by as much as 50%, and second, the
Clavicle. The clavicle, or when fused with its opposite humerus loses its proximal leverage and as a result, its
side counterpart, the furcula (wishbone), is not strictly power.
a part of the shoulder joint because it has no articular
component. Nevertheless, the clavicle possesses impor-
tant design features. First, the clavicle functions as a III ELBOW
secondary wing strut supporting the wing root (along
with the coracoid) and dampening lateral compressive The elbow or cubital joint is dislocated more than any
forces, which are exerted on the rib cage during fl ight other, often in conjunction with at least one fracture. A
by the downward sweep of the wing. A second impor- fracture-dislocation of one or both components of the
tant function of the clavicles is to indirectly connect the elbow is particularly onerous because it affects both
wing roots, thus assisting in the coordination of indi- the form and function of the joint.
vidual wing movements.

Triosseal Canal. The triosseal canal is an extraarticular III RADIAL AND ULNAR BODIES
channel formed by the confluence of the clavicle,

scapula, and coracoid. This canal provides guidance, There is no particular pattern to radial and ulnar frac-
leverage, and protection to the critically important tures. As with mammals, both bones are often frac-
supracoracoideus tendon, which attaches to the dorsal tured simultaneously. Displaced fractures occur more
humeral tubercle that elevates the wing during fl ight. often than nondisplaced fractures. Multiple fractures
Displaced fractures involving one or more bony ele- occur occasionally. Open fractures occur regularly and
ments of the triosseal canal suggest the possibility of are often associated with infection. Articular fractures
concomitant supracoracoidial tendon injury. Compres- may occur at either end of the antebrachium but in our
sion fractures can lead to secondary tendonitis, and practice are seen more often in the elbow and the same
expression fractures or exuberant callus formation is true of dislocations.
may result in impingement exostoses. Any alteration
in the size or shape of the triosseal canal can poten-
tially alter or interfere with the pull of the supracora- III CARPUS
coideus muscle-tendon unit and accordingly alter the
action of the associated wing. Carpal bones are rarely fractured but are often dis-
located as a result of serious distal radial and ulnar
injuries.
III HUMERAL BODY

The humerus is the largest, strongest bone in the wing, III METACARPUS AND DIGITS
but it is not the longest. The distinction of longest bone
goes to the radius and ulna, which are longer than The metacarpus is fractured occasionally, and as might
the humerus by about 10%. Proximally, a large broad- be suspected, the smaller minor metacarpal bone is
based, reptilian-like ridge, the pectoral crest, dominates more susceptible to injury than its larger companion,
the bony landscape. Situated on the opposite side is a the major metacarpal bone.

large angular bony outcropping, the dorsal tubercle, The first and third digits are susceptible to being

and in between lies the laterally compressed humeral torn away, especially the first digit, which is situated
head. in a vulnerable position relative to frontal collisions.
The humeral body is gently recurved and in The second digit is most susceptible to traumatic
places it is quite angular, especially when viewed in amputation and dislocation of one or both of it
cross section. Just above the metaphysis, the humeral phalanges.

2/11/2008 10:55:24 AM
ch009-A02527.indd 92
ch009-A02527.indd 92 2/11/2008 10:55:24 AM