46TH
ANNUAL
CONGRESS
OF
THE
SAEVA
SKUKUZA
16-‐20
FEBRUARY
2014
47
Radiology and ultrasound are often most useful when used together in a
complementary fashion for complete evaluation of the fetlock region. Marginal
osteophytes, osteochondral fragments, enthesophytes, and avulsion fragments are
also well visualised on ultrasound10-12.
Ultrasound will provide additional
information about soft tissue injury when it is associated with the fetlock joint or
suspensory apparatus.
Diagnostic Imaging – Ultrasound
Diagnostic ultrasound is a valuable, readily available adjunct imaging technique that is
of great utility for the evaluation of the collateral ligaments13, synovium and synovial
fluid14 in addition to the articular cartilage and subchondral bone in some regions of
the joint. Furthermore, the suspensory apparatus including the suspensory branches
and the distal sesamoidean ligaments are generally well evaluated using this
technique15. The benefits of ultrasound are that it is a very high-resolution technique
that can characterise small structures well. A limitation is that appropriate evaluation
of anisotropic structures (tendons and ligaments) requires the probe be
perpendicular to the collagen fibres. This can become problematic when evaluating
the most proximal portion of the sesamoidean ligaments at their attachment to the
sesamoid bones. For this reason, some authors have advocated for the use of MRI
over ultrasound in the evaluation of the sesamoidean ligaments stating increased
sensitivity for sites of pathology16. Furthermore, ultrasound remains highly operator
dependent with high variability in accuracy depending on skill and experience.
Diagnostic Imaging – Nuclear Scintigraphy
Nuclear scintigraphy provides functional information about the bones and to a lesser
degree soft tissue structures of the region of interest17. Scintigraphy is critically
important for the evaluation of stress (exercise induced) remodeling, particularly in
the thoroughbred racehorse, that, when excessive, can predispose the horse to
more catastrophic outcomes. Scintigraphy provides a very sensitive measure of
subchondral bone activity that can be of great importance when searching for either
subchondral bone injury or incomplete fracture of any of the articulating bones of
the fetlock. Negative scintigraphic studies should be evaluated with caution, as active
bone remodeling may be absent in the peracute and acute phases of an occult
fracture. Scintigraphy’s limitations are superimposition and its inherently lowresolution. This can be mitigated somewhat through the acquisition of orthogonal
images and special views such as flexed lateral images.
Diagnostic Imaging – Computed Tomography
The physics of image acquisition make computed tomography an excellent modality
for the evaluation of bone morphology. The fetlock region is no exception. In
general, CT has high spatial resolution, thin slices and rapid acquisition. Regions of
subchondral bone injury are generally, well demonstrated using this technique. CT
has been shown to provide superior osseous pathology (lysis, fracture) delineation
when compared to radiography18,19. Furthermore, intra-articular contrast, CT
arthrography allows for the identification of cartilage loss. Intra-arterial, regional
contrast enhanced CT (CECT) aids in the evaluation of regional soft tissues. CECT
scanning provides an assessment of the vasculature and highlights areas of increased
flow or permeability as expected in tissues with active inflammation. CT along with
CECT provides a very complete evaluation of articular fractures, the vascular supply
and the potentially contemporaneously injured soft tissues. In institutions where it is
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