Page 585 - Adams and Stashak's Lameness in Horses, 7th Edition

Lameness of the Distal Limb 551

Diagnosis
Clinical examination provides a high degree of suspi-
VetBooks.ir cion that OA of the fetlock is the cause of lameness.
Both radiographs and nerve blocks or a fetlock joint
block can help localize and define the fetlock OA.
Radiographs can help diagnose an underlying cause in
many cases, such as intra‐articular osteochondral frag-
ments (either as part of osteochondrosis or as an intra‐
articular fracture), subchondral cystic lesions (SCLs),
subchondral bone erosion, osteophytosis, or joint space
narrowing (Figure 4.132). Typically, digital nerve blocks
do not block fetlock OA, but a low four‐point block
significantly improves the lameness. 9–11 However, there
have been reports of horses with marked cartilage injury
in the fetlock joint improving with a palmar digital
nerve block. Direct intra‐articular anesthesia of the fet-
25
lock offers additional diagnostic benefits of achieving
complete resolution of lameness, access to a joint fluid
sample for analysis, and a direct portal for simultaneous
treatment. If the joint fluid appears hemorrhagic or
cloudy, an immediate synovial fluid analysis and culture
should be performed to rule out a septic process.
In the past, horses that responded to a direct block to
the joint but did not respond to rest or medical therapy
were candidates for arthroscopic surgery. Now, the use
of advanced imaging (CT or MRI) provides a more accu-
rate identification of the pathology and determination of
whether a horse is a candidate for arthroscopic surgery
or medical therapy (Figure 4.133). This is especially true Figure 4.133. Sagittal proton density MR image depicting
for horses with subchondral bone and articular cartilage marked cartilage damage of the distal third metacarpal bone
damage. Both CT and MRI are considered to be superior (arrows) along with marked sclerosis of the adjacent subchondral
to digital radiography to detect subchondral bone pathol- and medullary bone (arrowheads).
ogy in the metacarpophalangeal joint. 63,64

A B C

Figure 4.132. DLPMO radiograph of the fetlock (A) of a horse (arrow) due to marked cartilage loss. The joint narrowing can also
with a large periarticular osteophyte on the dorsomedial aspect of be seen on the oblique projection (C; arrow). Note that there are
proximal P1 (arrow). DP (B) and oblique (C) radiographs of another minimal other radiographic signs of OA in this horse other than
horse with severe narrowing of the medial aspect of the fetlock joint subchondral bone sclerosis in proximal P1 (B and C).