Page 699 - Adams and Stashak's Lameness in Horses, 7th Edition

Lameness of the Proximal Limb 665

analgesia is difficult, and desensitization of such a large bone, (4) narrowing or loss of joint space, (5) subchon-
portion of the limb occasionally alters the horse’s move- dral bone lysis, (6) new bone production of the distodor-
VetBooks.ir take 30 minutes to an hour to become effective. The central and third tarsal bones, and (8) ankylosis
sal tarsus, (7) bulging of the dorsomedial contours of the
ment. Perineural analgesia can be problematic and may
(Figure 5.67). The degree of lameness is not necessarily
tibial nerve is quite large, and it may take a prolonged
period of time for the analgesia to diffuse into and affect correlated with the degree or type of osteoarthritic change
the nerve. This block is not specific for the DT joints and detected radiographically. Early radiographic changes of
necessitates a methodical approach and sequential OA of the DT joints include periarticular osteophyte for-
desensitization of the distal limb, proximal suspensory mation, subchondral lucent areas, subchondral sclerosis,
area (proximal plantar region), and TC joint. Once these periosteal new bone, and narrowing of joint spaces.
have been performed without effectively eliminating the Certain radiographic changes such as periarticular osteo-
lameness, then a peroneal and tibial nerve block can be phyte formation or joint narrowing may be highlighted in
performed. the DLPMO and dorsoplantar projections.
Perineural analgesia techniques around the tarsus can Early cases of bone spavin have radiographic signs
also provide inaccurate results. For instance, analgesia that occur on the dorsomedial aspect of the tarsus that
of the DBLPN can influence DT pain, and according to progress dorsally. Some clinicians indicate the earliest
Dyson, intra‐articular anesthesia of the TMT joint can radiographic signs occur on the dorsolateral aspect of
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abolish lameness in horses with PSD (8% incidence). the tarsus. However, not all horses with DT pain have
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Therefore a comparison between the respective out- radiographic evidence of OA. Scintigraphic examination
comes of intra‐articular and perineural anesthesia is can be a helpful diagnostic tool in these cases and may
useful. A tibial nerve block can be useful to distinguish reveal subtle changes within the tarsus not detectable by
between DT joint pain and PSD pain, as anesthesia of radiographs. In contrast, some horses with radiographic
the tibial nerve will result in analgesia of the PSD with- evidence of OA are not lame. The correlation between
out significantly influencing DT joint pain. the degree of lameness and the extent of radiological
abnormalities is poor. However, even subtle radiographic
lesions can support the diagnosis in the presence of
Imaging appropriate clinical findings. There appears to be little
Radiography association between the duration and degree of lame-
ness, the response to intra‐articular anesthesia, and radi-
Radiography can be quite helpful in the diagnosis of ographic findings in horses with OA of the DT joint.
OA of the DT joints. Radiographic examination to evalu- Some lameness clinicians believe that horses with cystic
ate the DT joints should have the primary radiographic changes and subchondral bone lucencies on radiographs
beam centered on the DT joint spaces and focused tan- develop more severe lameness. In contrast, some horses
gential to the joint spaces to best interpret changes that with few radiographic signs are problematic in that
occur in these joints. Radiographic signs of bone spavin degeneration never progresses, and they remain lame.
include (1) periarticular osteophytes (“spurs”), (2) irregu- Some horses predominantly develop periarticular
larity and lucency at the intertarsal joint margin, (3) irreg- changes, whereas others have abnormalities confined to
ular width of the joint space and cysts in the subchondral the central and third tarsal bones and proximal MT3.

A B

Figure 5.67. Radiographic changes of OA of the distal tarsal periosteal new bone (A), and narrowing of joint spaces. The
joints can vary considerably including periarticular osteophyte radiograph on the right is a horse with juvenile spavin with moderate
formation, subchondral lucent areas, subchondral sclerosis, degenerative changes of the DIT and TMT joints (B).