46
46TH
ANNUAL
CONGRESS
OF
THE
SAEVA
SKUKUZA
16-‐20
FEBRUARY
2014
Multi-modality Diagnostic Imaging of
the Fetlock
Sarah Puchalski, DVM, DACVR, [email protected]
Multi-modality Diagnostic Imaging of the Fetlock
Fetlock pathology is common in equine practice regardless of horse discipline. In
racehorses, fetlock pathology can have a measurable negative impact on indices of
performance 1-3. Pathology or injury of the fetlock can involve any number of
anatomic components comprising the joint and the regional soft tissues. The fetlock
is comprised of the articulating bones, synovium and fluid, cartilage and subchondral
bone, joint capsule and collateral ligaments. Pathology of any subunit of the joint has
opportunity to lead to a common endpoint of osteoarthritis, loss of function and
lameness. Injury of the supporting soft tissue structures such as the suspensory
apparatus are also considered with the fetlock joint due to their overlapping clinical
presentations. It is arguable that identifying the inciting incident or pathology as early
as possible in the disease process can allow for directed therapies, appropriate
management and the best opportunity to minimise the resultant joint disease.
Furthermore, the fetlock is a common site of breakdown injury4,5 and the
identification of early pathology could aid in the prevention of catastrophic injury at
sites of pre-existing stress induced remodeling. The goal of diagnostic imaging in
fetlock lameness, remains the acquisition of an accurate and complete diagnosis/(-es).
Several factors will influence the ability to obtain this goal. Factors influencing the
accuracy and ability to detect injury include but are not limited to disease severity
and chronicity, the anatomic subunit affected, the location of injury on the anatomic
subunit, and the presence or absence of co-existing pathology.
Diagnostic Imaging - Radiology
Radiography of the fetlock will always be considered a mainstay of its diagnostic
work-up. Excellent resources exist for the procurement and evaluation of fetlock
region
radiographs6-8.
Marginal
osteophytes,
osteochondral
fragments,
enthesophytes, and avulsion fragments are generally well visualized using routine and
occasionally special radiographic projections. Although soft tissue swelling is readily
identified, defining the specific soft tissue injury is not possible using radiographs
alone, thereby necessitating additional diagnostics (ultrasound) to provide a complete
diagnosis.
Subchondral bone injury including lysis and incomplete fracture is more challenging
to detect on routine radiographic projections. Due to superimposition of the other
bones and the relative insensitivity of radiography for osteolysis, multiple different
projections are recommended. In the thoroughbred racehorse, radiographic
projections made tangential to the palmar /plantar condyle of the cannon bone are
recommended9. In other sport horses, where osteochondral damage is less well
understood, multiple projections of the fetlock should be attempted. These should
include variable proximal-distal beam angle on the dorsal palmar (plantar) projections
and slight variations (5-15°) of medial-lateral beam angle on oblique projections.
Making additional radiographic views is particularly important when there is a high
clinical suspicion of acute, incomplete fracture of any of the articulating bones.
46