Page 693 - Adams and Stashak's Lameness in Horses, 7th Edition

Lameness of the Proximal Limb 659

20 minutes to influence DT joint pain. Occasionally the are inconclusive. MRI of the tarsus has been useful in
response is even more delayed, making it preferable not the diagnosis of abnormalities that may not be appar-
VetBooks.ir addition, some horses with DT joint pain may respond cally. 13,14,21,45,83,125 Abnormalities seen with MRI include
ultrasonographi-
ent
radiographically
or
to proceed with further blocking for at least 1 hour. In
better to intra‐articular medication than either intra‐
subchondral bone injury of the talocalcaneal joint, bone
articular or perineural analgesia. bruising of the distal tibia, intertarsal ligament enthesop-
athy with associated bone edema, focal osteoarthritis
Imaging of the Tarsus (OA) in the plantar aspect of the DIT and talocalcaneal
joints with localized loss of joint space and subchondral bone
The equine tarsus is a complex joint and can be dif- sclerosis, and soft tissue injuries of the collateral liga-
ficult to accurately image due to the unique anatomic ments (CLs) of the TC and the proximal intertarsal (PIT)
arrangement and the superimposition of many struc- joints, as well as tendonitis of the deep digital flexor
tures. 59,60,77 Many of the changes that develop in and (DDF) tendon at the level of the calcaneus.
around this joint with disease are chronic. Radiographs
have proven to be useful to evaluate bony changes asso-
ciated with the tarsus. 23,36,63,106,145 While soft tissue swell- Radiography of the Tarsus
ing can easily be seen on radiographs, accurately Radiography is the most accessible and commonly
identifying the specific structures involved can be diffi- used imaging modality for the diagnosis of bone lesions
cult. Diagnostic ultrasound (US) is a very useful imaging of the tarsal bones such as osteochondrosis (OC), OA,
technique that can provide valuable information about or fractures. Radiographic interpretation of images of
the soft tissues of the joint, the articular cartilage, and the tarsus must consider the complex anatomy and
the subchondral bone surfaces. 32,35,59,116,140,148 Diagnostic superimposition of these bony structures of the tarsus.
US and radiology are considered the minimum imaging Radiographic examination evaluates bone pathology by
techniques to be utilized when evaluating a specific ana- the detection of subtle differences in bone density,
tomical region of the musculoskeletal system. For exam- trabecular detail, and cortical thickness. However, a
ple, ligament and tendon injuries frequently occur at the decrease in bone density of between 30% and 50% has
bone–soft tissue interfaces or insertions onto bone to occur before a change is visible radiographically.
(enthesis) with the earliest change often being early bone Many of the bony conditions that affect the tarsus
production. Both radiography and US are necessary to manifest abnormal radiographic findings that are
effectively evaluate the injury especially since US has located at the dorsum of the tarsus. Pathologic abnor-
proven to be more sensitive than radiology at identify- malities of the tarsus tend to be in specific anatomical
ing early periarticular remodeling and enthesis new areas, and soft tissue swelling is helpful to localize
bone formation. More information on tarsal ultrasonog- abnormalities. Radiographic examination of the tarsal
2
raphy can be found in Chapter 3. region is often performed to evaluate the distal tarsus
Nuclear scintigraphy may prove useful when radio- joints for OA (TMT/DIT) or to diagnose the presence of
graphic and sonographic examination fails to reveal sig- OC in the TC joint. Occasionally special projections are
nificant clinical information about the source of the needed to elaborate an area not clearly defined with the
lameness. 44,49,59,102,103,119,137 More recently MRI is being standard radiographic examination such as the flexed
utilized for tarsal imaging due to short‐bore high field lateral or skyline of the tuber calcis (TC) (Figure 5.62).
strength magnetic systems when other imaging modalities Other common abnormalities of the tarsus visible on

A B
Figure 5.62. Skyline (A) radiograph that was necessary to document osteitis of the calcaneus (arrow) and flexed lateral radiograph (B) that
revealed a large fracture fragment on the plantar aspect of the medial trochlear ridge of the talus (arrow) that was not visible with other views.