Page 108 - Veterinary diagnostic imaging birds exotic pets wildlife

104 SECTION I III The Birds

ance, delayed union should be anticipated. Recom- an implant incorrectly. Alternatively, owners may
mend 3-week progress check.” fail to restrict their pet’s activities in the critical
period before recently repaired bone fragments have

had sufficient time to solidify and are subject to
III FRACTURE HEALING THAT dislocation.
RESEMBLES INFECTION
Hypertrophic Nonunions
Certain types of callus can resemble infection. This is
especially true of long minimally displaced spiral frac- Not surprisingly, hypertrophic nonunions are most
tures where the callus resembles an infective involu- likely found in the wing, where regular movement
crum (Figure 10-11). Alternatively, some fractures may at the fracture site impedes interfragmentary vascular-
not only fail to form a callus, but may instead lose ization and discourages purposeful callus formation.

density. This latter appearance is usually due to either Instead, new bone deposition is confined to the
avascular necrosis or posttraumatic osteoporosis (see Figure ends of the fracture, making the bone appear
10-11). overly dense, flared, and often blunted, which is

an appearance sometimes referred to as an elephant’s
foot. Over time, humeral and radioulnar nonunions
III NONRESTORATIVE BONE HEALING: can become encased in a thick cuff of connective
THE MALUNION FRACTURE tissue, which is sometimes referred to as a false
joint. Figures 10-14 and 10-15 include examples of
Most authorities exercise some discretion when nonunions.
using the term malunion, generally reserving it for
moderate to severe deformities that might lead to Avascular Nonunions
some degree of disability (Figures 10-12 and 10-13). In
my experience, malunions are a potentially greater Fractures that have lost their blood supply are incapa-
concern in the wings of birds than in the limbs of ble of healing and eventually go on to become avascu-
mammals. lar nonunions. Unlike hypertrophic nonunions that
deposit nonpurposeful callus around the bone ends
(but not in between fracture fragments), avascular
Does Malunion Equal Dysfunction?
nonunions deposit little or no new bone (Figure 10-16).
There is nothing inherently dysfunctional in a mal- Instead, avascular nonunions result in a depletion
union fracture. Rather, malunion is a radiographic des- of the mineral salts from the original bone, causing

ignation, or categorization, that indicates only that a it to become dark and ill-defined compared with
fractured bone has failed to be fully restored, with or healthy bone. In some instances, the bone adjacent to
without treatment. the fracture appears to disintegrate or disappear alto-
gether, thus the term atrophic nonunion is used (Figure
10-17).
Time and Gradual Adaptation
Another type of nonunion is the unreactive, or non-
Generally, severe malunions can be accommodated reactive, nonunion in which the injured bone fails to

provided there is suffi cient time to make and practice change in any identifiable way, merely remaining qui-
the necessary compensatory adjustments to the control escent over time. Surgical revisions often behave in
surfaces of the affected wing. The principal purpose of this manner.
raptor recovery facilities is to provide time for gradual
adaptation.
When to Make the
Radiographic “Call”
III THE NONUNION FRACTURE As I proposed nearly 2 decades ago and based on
a similar proposal by Heppenstall, a fracture should
be declared a nonunion if it fails to show signs of
Radiographic Determination
healing in two consecutive radiographic examinations
A nonunion fracture is a fracture that fails to heal. Clas- made at least 3 months apart. Obviously, if a fracture is
sically, a clinical nonunion is defined by three things: palpably unstable, then its fragments are clearly

lameness, palpable pain, and fragment movement. ununited.
Radiographically, the two types of nonunions are
hypertrophic and avascular; the latter is also termed atro-
phic or unreactive. III SUMMARIZING CASE EXAMPLE

In this extraordinary example, the proximal radius and
Implant Failure and Dislocation

ulna of a snowy owl are first subjected to the grillwork
Implants do not fail, people do. Surgeons may use of a northern logging truck and subsequently to three
the wrong implants for a particular repair or apply Text continued on p. 115.

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