Page 245 - Adams and Stashak's Lameness in Horses, 7th Edition

Diagnostic Imaging 211

tissue injuries due to secondary bone change; however,
there are marked limitations in the ability for radiogra­
VetBooks.ir most accurate diagnosis and subsequently be able to
phy to evaluate soft tissue injures. In order to have the
provide the best care to the patient, visualization of
architectural changes within the soft tissues is essential.
Ideally, in these cases, other imaging modalities (i.e.
ultrasound or MRI) should be considered to comple­
ment the radiographic findings.
Skeletal abnormalities are identified radiographically
based on changes in bone density/opacity (reduced or
increased) and shape. Because skeletal lesions may only
be detected with radiographs after approximately 50%
change in bone mineralization is present, some condi­
tions such as acute osteomyelitis, early synovitis, early
cartilage loss/erosive arthritis, and minimally or non‐
displaced fractures may not be recognized on the initial
radiographic exam. In cases of acute trauma, it may take
up to 2 weeks before the bone changes are detected with
plain radiographs. It is also possible to have relatively
extensive articular cartilage damage with minimal radi­
ographic changes. Therefore, when clinical signs and
radiographic findings are incompatible, or radiographic
findings are insufficient, further imaging with other
modalities is often required.
In cases of comminuted fractures, it can be difficult to
completely characterize the extent and orientation of the
Figure 3.38. Lateromedial (LM) projection of the metacarpophal­ fracture radiographically. In these cases, computed
angeal joint showing palmar osteochondral disease of MCIII (arrows). tomography with multiplanar reconstructions should be
considered for surgical planning.
In summary, the practitioner should be aware of the
abovementioned limitations of radiography and that
the combined results of different imaging modalities
may be necessary to obtain a diagnosis. More impor­
tant, it should always be remembered that radiographic
changes do not necessarily represent lameness; there­
fore, a complete history and thorough physical and
lameness examinations are imperative in every clinical
situation.
NORMAL RADIOGRAPHIC ANATOMY

Recognition of normal radiographic anatomy and
variations of normal in the mature and immature horse
is essential in equine radiology to avoid erroneous diag­
noses. The normal radiographic anatomy of horse
extremities is presented for reference in the following
pages (Figures 3.40–3.88). A diagram accompanies each
of the radiographic projections, demonstrating the posi­
tion of the X‐ray machine and detector in relation to the
anatomical site of interest, as well as the angle orienta­
tion of the X‐ray beam. In addition, radiographic pro­
jections not commonly included in a standard
examination are described. A brief explanation of the
advantage of obtaining these projections is also included.
The nomenclature system used in this chapter is that
proposed by the Nomenclature Committee of the
40
American College of Veterinary Radiology, which uses
proper veterinary anatomic directional terms and
26
describes the direction in which the central X‐ray beam
Figure 3.39. Flexed lateromedial (flexed LM) projection of the
carpus. An area of lysis with a well‐defined associated osseous body penetrates the body part of interest, from the point of
(chip fracture) is present on the dorsodistal periarticular margin of the entrance to the point of exit (Figure 3.40). The standard
radial carpal bone secondary to traumatic hyperextension injury (arrow). abbreviation for the view is given in parentheses in the
Source: Courtesy of New Bolton Center, University of Pennsylvania. figure legends.